I know it’s kind of late to mention this, but I found a lot of situations where people had the same problem as me, so I wanted to post my solution and all the info I had on the problem to potentially save some people a ton of money and trouble. It may apply to any GM car with Passlock II, such as a Pontiac Grand Am.
I previously owned a 2000 Chevrolet Impala stealth police interceptor. It developed a strange condition where the car’s cluster would flat-line entirely, and if that happened, likely not start unless it wanted to do so. The instrument cluster’s gauges would drop to zero, and the “message center” would flash LOW FUEL, SECURITY, SERVICE ENGINE SOON and other ominous nasty messages in rotation. Essentially, all instruments would fail simultaneously. If this happened and the car was turned off, it likely would not start; I don’t recall if it turned over or not, but starting was almost guaranteed to fail.
After much poking around on the Internet, I learned of the GM cars’ vehicle anti-theft system (VATS) known as Passlock II (or Passlock 2 and I think sometimes it’s called Passkey II). Essentially, the car’s Passlock II security system would stop the car from starting if something was wrong with the system. This system consists of the key/ignition lock cylinder, the powertrain control module (PCM), the body control module (BCM), the OBD-II connector, the instrument gauge cluster, and the built-in radio. (Yep, all of that combined is the car’s computer!)
Here’s the trick about this system: all of these components (other than the ignition lock cylinder) communicate with each other via a one-wire serial data line which is referred to on wiring diagrams as “Class 2 Data.” The problem with Class 2 Data (I’ll call it C2D) is that it is spliced together at multiple connectors, and any one of those splices could go bad and fail to relay the C2D signal to the next device in the chain. In my case, the two purple wires running to the OBD-II connector, which linked the PCM under the driver’s side air filter box and the rest of the system, was failing to make a sufficient connection and the data would relay sporadically at best.
What does that mean? Simple: the powertrain control module, responsible for essentially all engine control, could not talk to the computers in the car that handled instruments, lighting, door switches, bells, and so forth. Unfortunately, that meant that the instrument cluster could not receive engine status information, and worse yet, the body control module would never talk to the PCM. Passlock II requires that the BCM send a password to the PCM to enable engine functions. Bad C2D connection between the two automatically means a guaranteed no-start condition and 10-minute no-start trigger, courtesy of GM’s Passlock II.
How did I fix it? It’s quite simple, really. I cut the two purple wires behind the OBD-II connector, spliced them both together with solder on BOTH sides of the cut, and communication was restored. Every problem with the car was immediately fixed, and that was the end of the saga. Sadly, this happened only after I rewired so many other things on the car that I had run short on options. Hopefully I saved you the trouble.
This is very helpful. I’ve got a 2003 Impala and have been having similar issues. Of course I call a tow truck because the car won’t start and as soon as we get to the mechanic’s it starts. They never were able to recreate the issue and they had it all day. The best they could tell me is that the security system may be failing.
I am looking forward to giving this a try, my 2003 Impala is doing very much the same thing. However has anyone had shifting issues associated with this issue. If properly reset the shifting issues go away but only until the next time the engine is started.
Where is this OBD thing located? I have no mechanical experience – is this something I could try on my own?
The connector is underneath the steering column. You need to at least be marginally handy with splicing and testing wires for continuity to find a break in your C2D serial wire; mechanical knowledge doesn’t really matter.
Too late I learned about the thousands of Chevy owners with Passlock problems. I bought a 2003 Chevy Malibu. It’s been sitting in my drive way for two weeks while I learned what a huge mistake I had made.
Do you think this would work on a 2003 Chevy Malibu, and is it something I could learn to do?
Thanks, hope is riding on your answer.
Did u solder the solid purple and solid pink together? If i took a wire tap and placed both wires in and snapped? Would that work as good as solder?
I don’t remember everything I did; you need to get a wiring diagram for your car. Also, if the connection is not secure, you risk it breaking due to vibration, so solder is the best way to go.
I live in a state that does mandatory emmision tests via the OBD-II connector. What effects will this mod have when emmision tests are done?
The DLC has 16 pins total. Pin 1, 3 and 6 – 15 are not used. Pin 2 is the class 2 serial data line. Pins 4 and 5 are ground. And pin 16 is battery voltage. My question is, how did your theory fix anything ?
The crimp for the Class 2 Data line is not just a connection from the OBD-II connector to the C2D bus; it crimps together the wire from the PCM and the wire from the instrument cluster + radio. Unfortunately, the connection between the two wires at the connector had stopped functioning properly, even though the run from the PCM to the connector itself was continuous. By adding a second splice behind that connector, it bypassed the bad crimp, fixing the problem. The instrument cluster and radio are part of the computer system (and specifically the security subsystem), so when that connection fails, the car’s security system misbehaves since the modules can no longer communicate.
hello would u mind helping me do this? im almost on same page just want to be sure
where is the bad crimp and the colors of it?
i have only one purple wire on my 02 impala at the obd2 plug in theres a purple a black and a grey with a stripe on it i beleive ive tryed alot of stuff also befor reading this it does make sence my cluster freaks out then i dont got any crank at all unless i reset the bcm fuze must be a bad conection
Purple is the serial data line. You need to make sure it is continuous between the PCM, BCM, OBD2 connector, cluster, and radio. Resetting a fuse shouldn’t fix it if that is broken though, so you may have another issue.
im asuming its shorting out somwere removing the fuze resets the bcm and cluster radio ect wen its put in it gets conection back somehow sometimes gota do it bunch of times car wont crank over dask and radio cut in and out what a stupid setup i dont have 2 purple wires in my obd2 port just one there is one pin with 2 but there not purple i wounder where my 2nd purple is the c2d from cluster is grey radio orange pcm dark green i know they all run to splice pack 205 right beside the ebrake pedal taped to harness and they alll ground there to comunicate together just were to resplice the wires? i have never had a gm with these problems b4 its deff not paslock cause i bypased that and next day wouldnt start gota be the class2 wiring radio will lock if u leave in run position wen cluster acts up with the no crank condition
i bought a 2001 impala with this same problem but they guy before me put a after market head unit in this car i have no looking through the schematics yet but is there anyway that this could be the problem? is there anyway i can by pass the after market head unit i am trying to get the original but i dont know if i will be able to thank you
Before anyone starts working on the OBDII port or connection with the bad connection with the purple CD2 data line should at least if they have a OBDII scanner hook it up and see if the system has any DLC codes first.
Mine had a U1064 code meaning there is no communication with the BCM and CD2 data line.
Yes, I am getting the security light but the car starts fine and runs fine at idle.
All the electronics work fine until the passlock II security light and the battery light starts flashing and then my door locks won’t engage when you put the shifter into reverse and the back up lights stop working.
Yes sometimes I get no starts and delayed starts.
If I solve this problem I will let you know how I fixed it.
Some people or web sites says it’s the BCM or the key cylinder but the GM TSB says if it’s trowing the U1064 code then there is nothing wrong with the BCM and they recommend that you inspect all the connectors and plug at the BCM.
What a nightmare this is.
Love the cars at least when all the bugs are worked out.
No CD2 to BCM means that the purple wire is “broken” somewhere between the PCM in the engine bay and the BCM. The OBD2 connector splice is where the wiring fault was on my car when I had it. Note that the radio and cluster are required components of the system too, and this code can mean no communication between them and the PCM also.
That’s the DTC code I was getting.
I already checked under the hood at the wire harness going from the PCM , Trans, to the main hook up just right over the battery.
I also tried to check to make sure all of the grounds are ok.
I hate trying trace down electrical problems in a car.
I had to stop myself today going any farther taking the dash apart in hopes of getting to the wire harness under the dash.
The thing is ? other than a few no starts and delayed starts the car starts fine and runs fine at idle.
Now going from stop to 40 miles an hour is another problem.
It seems the car has no power until you step into the gas, and when you go up hills, a clogged Cat maybe ?
Anyway, the car also has a battery drain over night and I know the Monte Carlo has a system in the electrical system to cause the battery to drain down to protect the electrical system in case of a electrical short.
I am up against the clock and time at this point because I have to get the car to pass state inspection.
I only thing that did not pass is that the back up light stop working and the door locks engage when the dreaded yellow secuirty light comes on at the message center and the red battery light.
Some times when I unhook the battery over night and hook it back up and run the car for a few mins everything seems to be fine even the door locks engage when you put the shifter into reverse and the back up lights working.
I sure hope I don’t have to dig into the dash to get to the wire harness under the dash to find a short.
The wire harness under the hood would be much more easy to work with.
Is the class 2 data line a certain standard copper wire ?
I unhooked the main connection at the battery and saw a thicker purple wire , is that the purple C2D ? should I test the continuity from that connection to the connection where the PCM is at ?
Towmow I will get a drop light so I can see better under the dash and try to trace down the purple C2D line, and make sure that the ignition and the Passlock wires or at least to see if the black wire going to the Passlock is a ground.
I did nothice that at the factory they had the 2 black ground wires that are connected to the frame or magesium frame for the dash was short of crushed under the alunimum bracker they used for the plastic dash part.
I know some of these parts are not the same for the impala, but, those years Impalas and Monte Carlo body and parts are almost the same. would they be the same in how the laied out the electrical systems ?
Update. finally got the car inspected but never figured out the problem with the C2D wire.
I pulled the whole wire harness out from under the engine bay and took it inside and worked on it for 2 days clenaing it up, putting new tape on it and checking for shorts.
No fun putting it all back in.
My advise to anyone ? leave auto wire harness removal and repairs to the pros.
So no shorts from PCM to at least the main block hookup next to the wheel well.
Next ? I will test the C2D line from PCM to the main block hook up next to wheel well.
God I hope I don’t have to take the dash apart just to trace down the C2D line short.
What I found out on my 03 Monte is from my Haynes repair manual by looking at the wire diagram is that the C2D line is dark green from the PCM to at least the main connection block or the black connection block attacted to the metal tube that is bolted to the wheel well and and radiator mount.
This part of wire harness is over the battery and is part of the main wireharnes and fuse box.
Then then part of the wire harness does down and is attacted to the frame of the car and wheel well located right infront of the where the idler pully and harmonic balancer.
When they say connector block they are not joking because that’s what this main wireharness looks like, a black block.
From there is does through the firewall and into the passenger comparntment under the dash where the real fun begins.
I believe I am having the same issue with my 2000 Impala, I made this video to show http://www.youtube.com/watch?v=VamB316mmlY
Seems pretty similar to what has been described, But I do not feel confident in doing the repair myself. Any advice on where or what type of shop I would take it to where I won’t be ridden for my money?
Anyone getting freaky electrical problems should first check all the ground wires under the hood first including but not limited to both battery cables.
Also, and this is a biggie check the main negative battery ground the really thick battery cable going from your battery to the engine block near where it meets the transmission bolt.
That cable will be near the starter for there will be a smaller black wire coming from that main cable from the battery to your starter.
Also from your battery cable where it’s bolted to your battery there will be a smaller black wire coming from the lead hookup to your battery to your body ground on the wheel well under the fuse box.
There’s a major body ground wire and I don’t know why GM went cheap on that one and used just one ground to the body.
Check all those grounds and make sure there is no corrosion, bad wiring, rust under the connection.
Unbolt it and clean it even use some sand paper to remove some of the paint.
Also, inside the car near the drivers left foot and the passenger’s right foot under the carpet where the bottom of the door frame where the door frame meets the floor pan there is a major multiple ground hookup connections.
Those need to be cleaned and remove the paint, bolt it back together and use some primer after you have bolted it back down to keep rust and corrosion off of it.
Under the dash after you taken the kick panel off near the steering column on either side of the steering column you will see 1 or 2 ground hook ups with 2 black wires coming from it.
Make sure those grounds are clean, and do not over tighten when you put them back because the dash frame is make out a magnesium metal.
I have not looked yet on my Monte but I think for the ground in the back of the car for the tail lights, back up lights, AMP, all the grounds back there is where the window deck is where the speakers are behind the rear passenger’s head.
I did check the wiring under the front passenger’s seat for the airbag and crash record module.
There is a class 2 data line running from that and sometimes when water get’s into the car under the front passenger’s seat it can cause corrosion, and damage the airbag module.
I don’t know what I did but I am not getting the yellow security light and red battery light anymore while driving.
The only problems I am getting now is the car won’t start and I have to pull the 10 amp BCM/Cluster fuse a few times to get it to start and a parasitic battery draw on the battery and it goes dead.
I’ll have to keep pulling fuses and leave the car sit over night and see if it helps and point in the right direction of where the problem is.
Where is the pcm located on the 2001 Impala?
The PCM is a box behind the driver side headlight. You can tell which box because it has a LOT of wiring coming from the top of it.
Count me in as having been frustrated by the a finicky PASSLOCK II problem too. My problem was caused a failing battery. When I checked the voltage without cranking it over is was fine at 14VDC. But when I cranked the engine over the voltage dropped too much and the Passlock freaked out and shut everything down and started the 10 min lockout. Naturally this didn’t happen consistently. Problem was resolved after I replaced the battery.
I recently started experiencing this. My question to you is what exactly do you mean by splicing the two wires together and soldering both sides of the cut? Do you mean after you cut one wire you solder the two ends of the same wire back together? Where do I cut the wires where I see visible damage to the wire? Do I remove the dash and inspect the C2D (purple wire) for damage? Please help me I am confused and getting frustrated with the instrument cluster randomly shutting off while driving.
Cut both purple wires that are going to a single common pin on the back of the OBD-2 connector. Strip the four cut ends you just made. Solder them all together. You may need a short piece of wire to jump them together since the wires don’t have much slack to take up. All you’re doing is bypassing whatever part of the crimp is not working properly anymore.
So I would have to remove the dash correct? Also, I’m still not sure where I’m supposed to cut the wires?
You don’t need to remove the dash unless the OBD-2 connector isn’t under the steering wheel. Just cut the wires about two inches behind the connector, then use some small wires to solder all of them back together. It can all be done from the outside of the car kneeling on the ground, reaching in.
Ok so after replacing both the PCM and BCM I am willing to try anything. The problem may afterall have been the C2D wire that you indicate here but I went with a mechanics word over yours unfortunately saying it was either the pcm or the bcm.
I finally went to look under the dash behind the OBD II connector. Unfortunately I only see one purple wire, one orange wire, a black wire, and a black w/ white line wire. The black and the black/white are the only wires that are right next to each other. See the link below to see pictures of the back of the OBD II connector.
https://www.dropbox.com/sh/suzcrfcd59w7u2w/3IIZF92_IX
In the Impala I owned, the purple wire on the back of that connector actually had a second purple wire crimped in with it. One purple wire went to the BCM/PCM and one went to the radio and instrument cluster. Since the cluster and radio are considered part of the security system, the disconnect caused by the poor connection between the two at the crimp point was causing my car to fail as if the security system was busted. I don’t see two wires on your OBD-II harness though. You need to trace that purple wire and find out everywhere it goes to. Getting a wiring diagram for the car is very important; you can tell what goes to what pin on what connector with one and you can then use a long piece of wire and a multimeter set to Ohms to determine if the wire is continuous and undamaged between the two points you’re probing.
Do you know where I can get a wiring diagram for my 2004 impala 3.4l base? Seeing as my obd ii is not the same as yours with the two purple wires, the method you stated above will not for me right?
Am I understanding you correctly if I trace the purple wire to see the closest spot where there are 2 crimped together. Then before that point where they are crimped I cut the wires a couple inches back, strip, then solder all four ends together and that should solve my problem?
I’ve spent far too much money and time trying to solve this in a short amount of time. I replaced the ignition switch, then the body control module and got it programmed at the dealer, and ive replaced the powertrain control module also. Total ive spent is well over $500 in parts and labor now I really cant afford anything. I just really need a solution to this as soon as possible. And I thank you very very much for trying to help me
You need to find an auto shop that has software or a website subscription where wiring diagrams can be obtained. Any shop using Mitchell software or the equivalent Web service has these.
At the end of the day, all you are doing is testing a wire for continuity. It needs to connect to the PCM, BCM, cluster, and radio. Tear the dash apart and start testing the wire. Find the furthest points (probably PCM and radio) and test them for continuity; if the ohm reading is too high or infinite, go down the line and test a shorter length. Eventually you’ll find the break in the wire by process of elimination.
I assume you know basic electronic stuff (Ohms and what they do when you just measure a wire, for example) and I don’t know anything about your skill level. I don’t know how helpful I am being. The bottom line is that if you suspect a break or connection failure in the C2D wire, you’re looking for symptoms of that. If your wire tests continuous between all four parts of the system, you don’t have a C2D wiring fault and need to look elsewhere.
What are the exact symptoms you deal with? What does the car do?
Well I have pretty basic knowledge. I know ohms are units of impendence. I need to buy a multi meter tear the dash apart but how do I check parts of the wire without having to cut and crimp together parts? Isnt that the problem in the first place?
What happens is when I am driving the instrument clusters guages stop reading correctly and I get the low fuel, service engine soon and security lights all flash. All guages go down to the lowest level as if the car were off. When the guages go the door chime comes on for a second or two and stops, the ac stops blowing COOL air but keeps the fans on, and the shift indicator led doesnt show what gear I am in but the odometer still shows and reads correctly. If I stop the car and shut it off and let it cool down for a bit say 15 minutes or so the problem is completely gone for a few minutes and then comes back again. Occasionally after the door chimes go off that indicate the problem is there again and I shut rhe car off when I go to turn it on it wont turn on at all but it will not flash the security light either for the passlock ii system. Before when this would happen on the stock radio it would say ” CAL ERROR” on the radio screen.
You may have more problems than the data wire in question, but it makes sense to check that wire first before checking anything else. You desperately need a wiring diagram. As for how to probe, the best way is to disconnect the connector for whatever module you’re testing the connection to and push the meter probe into the socket (or touch the pin, if the connector is male). This requires no cutting or splicing. Another option if that is completely infeasible is slicing the insulation off in one place but not cutting the wire itself, and testing against the bare wire. Be sure to use electrical tape to cover it when done.
Get the wiring diagram and start testing. You’ll need a long (25 feet or so) piece of wire to be able to reach the PCM connector and any connector inside the cabin for continuity testing! It looks silly but it gets the job done.
If it wasn’t the pcm nor the bcm and possibly not this c2d wire what could it possibly be? Do you think its time to start setting money aside to replace this car?
I need to look for a multimeter and find a wiring diagram now. Im searching the internet for those.
Now for the long wire I already have plenty of wire stored somewhere but I am not sure what I would do with the wire? Is it to connect the end of the wire to the connector pin and the other end to the multimeter?
Yes, you’re trying to extend a connector pin because your meter (available in any Walmart wherever the wall outlets and surge protectors are sold) will have probes that are only a couple of feet long. You need to extend some connections within the distance the meter can reach.
You should probably start saving money to replace the car, just in case you can’t figure out what’s wrong. Sometimes the time and expense is too great to be worth it, especially when you can get a used beater car or small motorcycle for dirt cheap. When my car’s rims finally stopped holding air due to salt damage where the tire seats on the rim, I picked up a 250cc motorcycle and rode it for a good while. The rain was no fun, but a waterproof bag with work clothes and a towel (and temperatures not being too low) got me by. Sometimes you do what you have to to get by.
I recommend making this problem a challenge to fill your spare time. You know your primary computers are good and you know that you probably have wiring issues, so get your hands dirty and trace out all the wires you can! You’ll either figure it out or become confident that you exhausted all possibilities before giving up. Please don’t spend more money to fix it, though. I gave up on my Impala after fixing the data line issue because of an automatic transmission sensor that was throwing a code and my lack of knowledge and experience with transmission work. Always know when to just give up.
If all else fails, get a Honda Prelude. I own one and I don’t think there’s anything on it I can’t figured out how to fix.
I think I finally got it fixed!!!!!! I suspect it was in fact the BCM because it would happen minutes after driving and the problem would go away if I let the car cool down.
NOTE: After I replaced the BCM the car was just fine I test drove it for 45 minutes and everything was perfect. I had the air bag light on so I had to take the car to have the BCM programmed at a chevy dealer. They did it and quoted me for 1hr labor ($140) and I disputed I was told it would only take 30 mins labor to JUST reprogram it. They did it for the 30 mins labor quote and ended up coming to me with the keys “bad news”. Told me that the guages weren’t working and thedoor chime would beep right before they went (EXACT same problem I had before replacing the BCM myself). And told me I should come back during the week to have that diagnosed. I asked what do you think it could be now and he told me either the PCM (not true I replaced that recently), or wiring and it would take 5-6 hours labor to diagnose this… After taking it from the dealer it was so much worse than before it wouldnt even start literally more than 60% of the time. I wenthome and after 2 hours of jiggling the pcm box and Iits connectors found the problem that the dealer caused. They left the connector that is under the driver side engine bar that goes from the strut area to the radiator area loose. They have no reason to be touching that if they were just programming the BCM. After tracing where the wires from that connector they go from the PCM to the inside of the car by the area where the BCM is located. Have been driving it for 2 days so far and all is well!
This is why I don’t trust any mechanics but the one I go to.
P.S. Happy New Year and thank you for your help!
I recently started experiencing this. My question to you is what exactly do you mean by splicing the two wires together and soldering both sides of the cut? Do you mean after you cut one wire you solder the two ends of the same wire back together? Where do I cut the wires where I see visible damage to the wire? Do I remove the dash and inspect the C2D (purple wire) for damage? Please help me I am confused and getting frustrated with the instrument cluster randomly shutting off while driving.
I have a 2000 chevy impala and getting the same issue but I am getting 12 volts at my DLC #2 which is the data line signal why?
I don’t know. I don’t have the car anymore.
My 2005 impala does not start in the morning and sometimes out of the blue. When I unhook the battery and ignition control module and re-hook them my car starts on the first try. The pass code light never comes on in the message center. What could be causing this to happen?
I am not a mechanic and don’t have specific experience with these cars beyond the problem I documented. I can speculate that your car is probably not starting due to some sort of wiring fault with the security system but I have little basis for that speculation. I haven’t touched an Impala in almost a decade.
I have a 2003 impala and I have to wiggle my pcm/bcm/clstr fuse around until the check engine light comes on and stays on and then it will start but still dies at times. Mostly at stops or deceleration. Its annoying but may help. When the engine dies it also flashes the same messages in the message center.
Dash cluster inop intermittantly. Everything goes blank. Had been in shop 4 times with no ability to duplicate. Guess what? Only did it with a passenger in the front seat. Seems that there is a harness under the seat that is tied directly into the instrument cluster. The harness installation is faulty causing a disconnect when there was pressure applied to the seat. Re-route and mount harness. Repair any frayed wiring. Problem solved. What a headache that was for a year.
Okay I have a quick question I have a 2007 impala and the battery keeps dying when I checked for a drain I have to pull four fuses to fix the drain I pulled the radio fuse the int Lhts/pnl dim fuse the int lhts fuse and the bcm fuse do you think I have the same problem going insaane repairing connections
Can you please tell me exactly what wires should I splice on my 2004 chevy impala.
I don’t see the two purple wires. Mines have a orange, black, purple and another with a white line running through it.
My obd2 is not reading when I hook my scan tool up it says no link and the is not starting so can you give me some information of you know what two wires to splice to get the pcm and the back to talk…….
Thanks in advance
The wires are purple on the 2000 Impala I had. Look for a pin on the OBD2 connector where two wires of the same color run to the back of the pin. A wiring diagram will tell you the color you need.
can u put a jumper wire in as temporary to see if that fixes the problem
I am dealing with the same issue right now and my 2008 Impala will not start. I was driving down the road when all the sudden all my gauges went to zero 5 minutes after that the radio when off. I pulled into the grocery store and came back out and my car would not start I do not know what the issue is but by looking at your description I think that is the issue. It has been doing this on and off all summer long I will reach under the steering wheel grab a bunch of wires and shake them around and usually it starts back up but not this time so I need some serious advice because I have got to get to work and I need a vehicle desperately so any advice would be a big help thank you so much
Can i use a dashcluster from a 02 impala in my 05 impala the 02 one has more gauges