Security Light, No Start

[james_boston]

I have a 2003 Duramax that's been giving me a run for my money recently.

Had a dead battery so jump started it to get it in the garage. Went to jump start it again and noticed after hooking up cables that I had no engine light on the dash with key on, engine off. Also noticed steady theft light on. Long story short on that one, the TCM had a dead short, was popping PCM-B fuse and taking the whole network down. TCM replaced, fuse no longer popping and truck started right up (new batteries too). Theft light was still on but the truck started. Cables were NOT reversed when jump starting.

Made it a few miles from home and truck died. One of the battery cables was loose and I'm guessing that's why it turned off, but now it won't restart. Tried the security relearn and didn't seem to work. Went into the BCM security data on my scanner and some things caught my attention. [My thoughts to right of data]

Passlock Power: Active [OK, indicates 12 volt power supply from BCM]
Passlock Data Voltage (key on engine off): 5 volts [OK, should be between 0.86 and 5 volts)
(cranking position): 2.49 volts [OK, should be reduced from KOEO voltage based on Passlock resistance]
Content Theft State: Off [OK, not in theft mode]
Content Theft Lamp: On [OK, indicates a problem with passlock system. Would not necessarily keep vehicle from starting]
Passlock State: Normal Decision [OK, normal, also switches to Ignition Off with key off]
Passlock Code: 12 [Potential problem! Should be between 1 and 10 based on the resistance of my Passlock system. Likely causing alarm in BCM that's preventing relearn]
All the timers (tamper, auto learn, etc.): 0 [Likely indicative of Passlock system not talking correctly with the BCM]
Key Cycles: 0 [Again, assuming Passlock system is not communicated correctly with BCM]

Only code present is a U1000 for Class 2 Data errors. It is not a code within the BCM. It populates in the Radio, IPC, and SRS modules.

Worth noting - service data seems to indicate if the Passlock system is activated it is flashing on the dash. When the light is solid, it indicates a problem with the Passlock system, but wouldn't keep the truck from starting. This seems to align with the truck initially starting after the new TCM with the security light on. I have no blown fuses that feed the BCM. The timer not showing the relearn is in-progress seems to be related to the Passlock Code not being within the BCM's expected range (1-10). I don't know that the Passlock component failing would cause the Passlock Code to be sent to the BCM as 12. It's making me think the BCM may be the problem. Since the system doesn't appear to be talking with the BCM correctly, I'm also not sure if the resistor bypass trick will work to eliminate the Passlock system (relearn doesn't work so wondering if it won't be able to learn the resistor either - also don't want to cut the wires to the Passlock system for it to not make a difference). Also worth mentioning the ignition occasionally sticks when switching from OFF to ACC.

Truck is rust-free, 26x,xxx miles. Visual inspection of grounds are OK.

Any tips/direction would be appreciated.

 

[james_boston]

Adding more findings:

The truck is in fail enabled mode, meaning it's not the theft module directly keeping the truck running. Passlock light is indicating hard system fault, likely the Passlock Code issue. Injectors are not turning on. Scan tool is reading 200 psi fuel pressure while cranking, and only 0.2 volts read at the injectors. Still unsure if the BCM could be killing the injectors due to an internal fault or if it's more likely an issue on the fuel module side/air getting into the system. For some reason my scan tool doesn't give me the injection status in the security data like I'd expect (using an Autel MS906BT). I'm not sure how much resistance there should be on the fuel primer button but I can relatively easily press it all the way down with my palm. Will continue testing and report back if I find anything else useful.

 

[Ron Nielson]

Only code present is a U1000 for Class 2 Data errors.

I would work on getting this resolved. When the communication lines don't work, problems persist until they are resolved.

 

[james_boston]

Should the Theft Deterrent Module appear as a module in scan tool data separate from the BCM? My scanner is pretty powerful but only lists modules that are communicating. When they don't communicate, it just doesn't list it.

 

[1FastBrick]

I believe the theft deterrent is handled by the BCM. It needs a hand shake with the ECU to allow the vehicle to run.

 

[james_boston]

Thank you guys for the feedback. I appreciate it.

I scanned another Duramax and the theft data was all contained within the BCM. I think you're right about no separate theft module. The U1000 seems to be a history code. It has not returned since clearing.

I ended up putting in a new to me BCM for $40 (have not programmed my VIN in yet). The Passlock Relearn is now initiating and security light is flashing with key on. It completes one 10 minutes cycle (security light turns off with key on). After switching ignition off and back on after 10 seconds it goes to a solid security light and won't initiate the second relearn cycle. Live data shows Tamper during the first relearn when relearn timer is counting. On the second key cycle it goes to Normal Decision without the timer increasing. If I try to crank it after the first relearn, it does not start, but then it lets me do another a key relearn again. The Key Cycles data constantly pid shows 0. (I assume this should be based on the number of relearn cycles done??)

I think I'll do the resistor trick now along with getting my VIN programmed into the BCM and see how that affects the relearn. The resistor trick should hopefully eliminate the Passlock sensor as being the problem.

 

[mojito5000]

My wife's GrandAm that she had while we were dating was the worst for the Passlock crap. I did the resistor fix on it and everything was good after that, but I can't count how many times I was stuck in a parking lot waiting the 10 minutes for it to relearn the key because I didn't keep the key on start until the car started. Luckily my truck is a 2001, and the passlock isn't fully enforced.

I'd take care of the VIN correction on the BCM before anything. I don't think the resistor will work unless the BCM is matched with other computers on the truck.

 

[james_boston]

I wanted to follow up on this post.

I started doubting the BCM being the problem based on what I read in service data. Before paying a shop to reprogram the new BCM, I threw a new fuel filter on it. The primer on the filter housing stiffened up a lot more than previously. I thought maybe it was losing prime so had someone pump the primer while cranking it and it started up. Put a new housing on it and have been driving it a couple weeks without any issues. Ultimately I'm just out the $40 on the used BCM.

I still have the theft light on the dash which seems to indicate there's some kind of issue with the passlock system, but because that issue began with the truck running, it doesn't keep the truck from running.