V1 Gremlins - multiple symptoms SOLVED

[escapepilot]

Well…that didn’t change anything. I’ve checked all grounds from plug to chassis and there are all ok.

Low speed data wires all check out with continuity between every point.

High speed data had check out last week.

I’m back to my original hypothesis but I haven’t determined how to test it yet. I need to study the wiring diagrams more (thanks for the AllData Ross). My theory is the issue is in the starting circuit. Why? Because when everything is right, I will get the brief Anti-theft light on the cluster but when it’s not working, I don’t even get that light just putting the key into the Run position. I’m leaning towards a fuse box pcb problem because changing relays didn’t fix it AND the high beam issue seems to be a problem with the pcb mounted relay as I get voltage to the fuse box plug but not to either high beam fuse.

I’m open to ideas but in the meantime, I’m going to study the diagrams and see how I can bypass that run crank relay. Oh, if I put 12v to the purple starter wire, it will crank and run but no data to the DIC in the cluster.

 

[Gtstorey]

Later models won’t have power on the hi beam fuse until the relay is closed since the fuse is after the relay. I assume the earlier models are the same. Are you getting a ground signal from the bcm to close the hi beam relay?

 

[escapepilot]

Later models won’t have power on the hi beam fuse until the relay is closed since the fuse is after the relay. I assume the earlier models are the same. Are you getting a ground signal from the bcm to close the hi beam relay?

Maybe not. I’ll have to study how to check that.

On the starting side, I’m getting 12v to the run/crank relay through the park/neutral fuse to the crank relay (pin 87 on the relay). I also get 12v to the crank relay pin 85 ad to PCM C1 pin 54 once the clutch is pressed. I have continuity from relay pin 86 to PCM C1 pin 48 which is the starter relay coil control. Double checked continuity on high speed data from BCM to PCM and both wires check good.

The only thing I can think of now is it’s internal to one of the modules.

 

[Ross]

Well…that didn’t change anything. I’ve checked all grounds from plug to chassis and there are all ok.

Low speed data wires all check out with continuity between every point.

High speed data had check out last week.

I’m back to my original hypothesis but I haven’t determined how to test it yet. I need to study the wiring diagrams more (thanks for the AllData Ross). My theory is the issue is in the starting circuit. Why? Because when everything is right, I will get the brief Anti-theft light on the cluster but when it’s not working, I don’t even get that light just putting the key into the Run position. I’m leaning towards a fuse box pcb problem because changing relays didn’t fix it AND the high beam issue seems to be a problem with the pcb mounted relay as I get voltage to the fuse box plug but not to either high beam fuse.

I’m open to ideas but in the meantime, I’m going to study the diagrams and see how I can bypass that run crank relay. Oh, if I put 12v to the purple starter wire, it will crank and run but no data to the DIC in the cluster.

The purple starter wire was my way of starting the car for about 6 months while I debugged the GM high speed LAN. Same issue with the DIC cluster.
For me, it was replacing the data electrical connector at the power steering, and replacing the power steering unit. You might have continuity on your GM high speed LAN wires, but I bet you have an intermittent connection.

 

[Gtstorey]

If this was me, I would start at the key and track down all signals all of the way through. Unfortunately this may still not get you all of the way since it is possible certain data isn’t getting since. A high end scanner or tech2 clone might be needed so you can see the status of all the signals and look for the abnormal reading.
I wonder what they do when the reset the odometer? Maybe the left something loose inside the BCM?

 

[escapepilot]

I may have found something else to check and I need a second opinion. I get 12v on the starting circuit 5199 which is the yellow wires from ignition switch through BCM to fuse box run/crank relay. I checked voltage at the ECM/Trans fuse and do get at least that far.

I also get power through the brown accessory circuit 4 BCM C4 and at the theft module brown pin 2.

What I can’t confirm is the white 1390 circuit. Key to START, white wire at pin 5 to BCM C2 pin 56. I’m getting no voltage with key to start. I also get no voltage on the white/black circuit 1073 which is supposed to be 5v reference. Nothing at the BCM C2 pin 62 nor at the ignition switch.

 

[Gtstorey]

Post the wiring diagrams.

 

[escapepilot]

Power Distr 2006 Cobalt

Charge Start 06 Cobalt.

Anti theft 06 Cobalt

And using the AllData connector diagrams.

 

[escapepilot]

 

[escapepilot]

I’ve been using fig 3 on the power distribution diagram.

What I haven’t found yet is where that 5v comes from. Is it stepped down in the BCM or does the white wire from the BCM supposed to be 12v and get stepped down in the ignition? Also, it shows run/crank and off/run/crank relays as part of the BCM logic. Are those different from the ones in the fuse box?

 

[Gtstorey]

It’s showing the relays as part of the under hood fuse box. The 5v is being supplied by the bcm. The question is what logic is required for it to turn the 5v on. Is it on all of the time or is looking for permission from the Theft Deterrent Module to turn on the 5v? I tried to find what the newer model service manual says and can’t find an answer. Maybe someone has access to theirs to check.

But I think you are getting close. If it’s waiting on anything else to turn the 5v on, it pretty much has to be the TDM. Have you confirmed that it’s getting power. One should be 12v all the time, one should get 12v when the ignition switch is turned.

 

[Gtstorey]

Are you checking for voltages at the bcm by backprobing with the connection plugged in?

 

[Gtstorey]

I think the white wire may be supposed to have a varying voltage of either 3 or 4 volts on it depending on where the ignition switch is turned but it would need the 5v to get there anyway.

 

[Gtstorey]

Also, it shows run/crank and off/run/crank relays as part of the BCM logic. Are those different from the ones in the fuse box?

These are not the relays. It is trying to label what state the ignition switch is in when these connections see voltage.

 

[escapepilot]

But I think you are getting close. If it’s waiting on anything else to turn the 5v on, it pretty much has to be the TDM. Have you confirmed that it’s getting power. One should be 12v all the time, one should get 12v when the ignition switch is turned.

I feel like I should know this, but I haven't come across the TDM abbreviation yet.

Are you checking for voltages at the bcm by backprobing with the connection plugged in?

Both ways at the BCM, PCM, and other modules. At the fuse box, I've either unplugged or checked w/ the relay removed or at the fuse.

It seems like the BCM generates the "5v ref" signal when the key is in the run or start position. If I'm getting no voltage at all, I am thinking the problem is within the BCM. What I haven't figured out is how that affects the starting side of the equation. The Starting and Charging diagram doesn't do a good job showing the connections for the Run/Crank relay. With key on RUN, I have voltage at that relay. I also get 12v to the Crank relay. I get voltage to one side of the coil in the Crank relay when the clutch is pressed, but I get nothing at PCM C1 pin 48 which is labeled Starter Relay Coil Control.

 

[Gtstorey]

TDM is Theft Deterrent Module.

The older diagrams are harder to read in some portions and easier in others. I'll try and remember to post the newer starter diagram this evening since it seems to work basically the same.

The ECM uses logic to decide to ground C1-48 to close the relay crank the car. Part of this logic is whether the 5v signal is returned to the BCM. Since that 5v supply is also within a "logic" box it may need certain conditions to be met to turn on the 5v supply (possibly the TDM). This is where it gets tricky trying to diagnose with just a DVM. You can't really know what all of these logic conditions are and really need to be able to interface with these modules to see if they are "happy". The higher end scanners will tell you the status of all the inputs and outputs, such as whether the TDM conditions are met.

I have heard that the TDM just cuts fuel when it's active and will typically crank, but I don't know how true that is.

 

[escapepilot]

That has the potential to explain multiple symptoms too. I don't think it's in the TDM as all of the circuits tied to the TDMon the Anti-Theft diagram are showing voltages under the proper key positions, but it could be internal to that logic circuit. Narrowing it down helps.

 

[Gtstorey]

It's all about what is sent over the data network after you have confirmed that the modules are getting the correct power/ground. The modules are basically individual computers talking to each other over the data network.

Have you tried a different key?

PASS-Key® III+ Operation Your vehicle is equipped with PASS-Key® III+ (Personalized Automotive Security System) theft-deterrent system. PASS-Key® III+ is a passive theft-deterrent system. This means you do not have to do anything special to arm or disarm the system. It works when you insert or remove the key from the ignition. When the PASS-Key® III+ system senses that someone is using the wrong key, it prevents the vehicle from starting. Anyone using a trial-and-error method to start the vehicle will be discouraged because of the high number of electrical key codes. When trying to start the vehicle if the engine does not start and the security light on the instrument panel cluster comes on, the key may have a damaged transponder. Turn the ignition off and try again. If the engine still does not start, and the key appears to be not damaged, try another ignition key. At this time, you may also want to check the fuse, see Fuses and Circuit Breakers on page 5-93. If the engine still does not start with the other key, your vehicle needs service. If your vehicle does start, the first key may be faulty. See your dealer who can service the PASS-Key® III+ to have a new key made. In an emergency, contact Roadside Assistance. See Roadside Assistance Program on page 7-7. It is possible for the PASS-Key® III+ decoder to “learn” the transponder value of a new or replacement key. Up to 10 keys may be programmed for the vehicle. The following procedure is for programming additional keys only. If all the currently programmed keys are lost or do not operate, you must see your dealer or a locksmith who can service PASS-Key® III+ to have keys made and programmed to the system. See your dealer or a locksmith who can service PASS-Key® III+ to get a new key blank that is cut exactly as the ignition key that operates the system

 

[escapepilot]

I only have the one key, but the problem was intermittent till recently so I am hesitant to think it would be a key issue. I am also not getting ANY security light on the cluster at this time. I did previously, but not now. I think it is related to the start relay coil command not sending the signal to wake up some of the other systems.

 

[Gtstorey]

Which one are you calling the start relay coil?