Bare with me, this has been a painful week. So I took my car to the body shop to have the bumper and fenders replaced. When he went to detail it, the car would not start. I was able to get it home by jumping the red wire to purple wire at the TDR to start the car. I also have had parasitic battery draining issues since this winter but unsure if it is related. I did notice relay 42 "CTSY LP" clicking until my battery died while I was tearing apart the dash. I'm not sure what this relay pertains to and haven't been able to find much info on it.

I've watched just about every "try this" video with no luck. I've checked all the fuses, clutch switch, ignition switch (cleaned the contacts). I finally buckled down and started checking voltages after looking at the wiring schematics. I have 12v all the way from the ignition switch to the yellow wire going to C2 at the TDR. However, I do not have voltage coming out the other side (yellow/ black) going to "starter enable". I know the TDR needs to close the contact to allow voltage to the starter solenoid, but I'm stuck at the TDR. I bypassed the passkey with 523ohms of resisters (key 2), but I'm still not getting voltage through the TDR. Is it possible I just had a relay fail?

I also found the relay next to the TDR (looks the exact same just to the right on TDR) disconnected and scotch tape over the end of it... I have no idea how long its been like that and I cannot find any information on it.

From all this, my questions are:
What is relay 42 (CTSY LP) and does it have any importance to my issue?
Does the TDR contact close from 12v coming from the clutch switch or does it close from the passkey resistance? I would assume it would be both...



What is the relay next to the TDR?

I have considerable electrical troubleshooting experience, but I'm used to reading ladder diagrams on industrial machines, not vehicle schematics.

 

You're close, but you are making this way harder on yourself than it has to be

Check right at the TDR connector (unplugged not back-probing).

At C2 (yellow wire) - Clutch in, key to start, you should have 12v
At A1 (yellow/black wire) - Clutch in, key to start, you should have a ground from the BCM (BCM reads passkey resistance and provides a ground for the relay coil, plus communicates with the PCM to enable fuel)

If the above is good, the relay is toast. You already know jumpering works, so that tells you that the passkey resistance is correct, and everything from fuse 50 to the S-terminal on the starter is good.

Not sure why you are fixated on relay 42....relays will chatter as the battery voltage diminishes. Must have a fully charged battery!

 

okay, great thanks for the insight. As to relay 42, it was chattering a lot more than it should have been id think... oh well. Any idea what the relay next to the TDR is? still not sure why it was unplugged...

 

Does your steering wheel lock? The relay next to the TDR is the column lock relay. I agree with lucky about the BCM, but disagree about the passkey working because you can jumper at the TDR. The jumper at the TDR removes the TDR completely out of the starter circuit, as you are sending 12v directly to the starter, the key doesn't even have to be inserted. I helped a fellow c5 corvette owner with the same problem which turned out to be that the BCM itself did not have a good ground.

 

I don't know off the top of my head... I will have to check, I've never really paid attention. I do get the remove key wait 10 seconds alert but the fuel shut off has been tuned out up to I think 200 mph instead of 2mph. If I had to guess, I would say no it does not lock currently.

As far as the TDR, I agree because I can start it without the clutch switch when I jumper purple to red at the TDR. I did order a GM sensor to throw at it and see if that takes care of it. If not ill start looking into the wiring from TDR to BCM and what not.

 

What sensor did you order?

 

oops lol.. TDR, my mistake.

 

 

so I’ve been tinkering with it all morning and here’s where I’m at.

I pulled the connector from the BCM with the passkey wires and checked the resistance received from my key. It’s right on the money at 523ohms.
I hooked my meter up to a known good ground and the yellow/ black pin on the TDR connector (relay not connected). With my meter set to resistance and trying to crank the engine, I don’t complete the circuit.
with this, I hooked an external ground up to the yellow/black wire and plugged it back in, the car starts.

I put in the new GM relay I ordered, removed the added ground, and still no crank…

I have 12v to the yellow wire at the TDR, correct resistance from the key, and no ground on the yellow/black wire at the TDR from the BCM… everything else works in the car (lights, radio, hvac, etc) and the connections at the BCM plug all seem tight.

is it possible just the ignition enable part of the BCM took a crap?
would there be any downfall from just connecting a ground to the TDR yel/bl wire permanently other than completely bypassing the security system?

 

....by "I don't complete the circuit" , you mean the meter continued to read open / OL/ infinite resistance? You can also use a test light as a double check. Test light connected to B+, and probe at the TDR connector A1.


I assume you still have no codes?




Yes.

Not sure what the BCM monitors on that circuit. It would be worth inspecting the BCM PCB first for evidence of corrosion due to moisture, which is a common problem.