I bought a salvage c7 corvette that wouldn't start. It does not crank, when I engage the key fob and the start button with the clutch press it says to press the clutch. Its not reading that i am already pressing the clutch. I tried using my code scanner to teach clutch position but it says that ignition must be on and engine off. I already replace the ignition relay and re program the ecm. I am out of ideas on what to do next. I know that the relay is not receiving ground signal from the ecm to activate the relay. But the ecm does everything else so i dont think its the ecm since it has already been repair. If anyone has any suggestions would be much appreciated thank you.

 

Curious to what year this is but my suggestion doesn’t matter. You should be able to HOLD the start button in for about 8 seconds & the car will enter diagnostic mode which should allow you to run your code reader & do what you want to try.
PS: Reason I asked about year is 19s have to have clutch in PLUS foot on brake to start. Don’t imagine you bought a 19 salvage car but that’s the unknown.😬

 

Ill try doing that, holding the engine start for 8 sec see if it gives me any new information. Its a 2014 z51. On the code reader it only mentions that the clutch needs to be learn.

 

It works now!!! Holding the power button reset it everything and it turn on

 

Awesome dude! Good luck with the car 🚘.

 

Reviving this old thread. I have the same symptom as the OP. Press start. Center of cluster activates but not the outer wings containing the tachometer and other gauges. Starter will mot engage. Message to depress clutch is shown. Power locks work but hatch will not pop either with key fob or button on dash.

Hold start button to enter maintenance mode as described above. Cluster comes alive, hatch works, starter works. Everything fine until engine shut off, then have to use same procedure to start every time.

We knew the clutch switch was not the problem but it’s a cheap part so plugged in another one no change. Dealer has worked with GM support, even GM does not have a solution. Issue is not common but has been discussed in other threads. Holding the start button to get maintenance mode is a stop gap can’t do that forever.

Did the OP ever find the true source of the problem?

 

I read your profile and it says your a GM car dealer…if so your Techs can’t find the solution to your no start…I know dealer techs follow their flow chart because most are weak at diagnostics…have they done that ??…its probably best to start a new thread with EXACTLY all your symptoms…there is only so much we can do over the internet…communication issues can cause a no start…have the Techs been able to scan all modules to see if they can communicate with ALL ??…they need to look at INPUTS with a scan tool that will allow the car to start.

 

Tell your guys to remove the starter relay and probe terminal 86 with a 12 volt test light connected to GROUND…when you push the start button the test light should light !!

 

FROM THE FSM:

Circuit/System Description

The ignition mode switch has two LEDs that indicate the vehicle power mode. When the vehicle is in the off mode, both LEDs will be off. Pressing the ignition mode switch button once (without the brake pedal applied), the vehicle enters the accessory mode and the amber LED (Accessory) will illuminate. The accessory mode has a 10 min time-out to reduce battery drain. Pressing and holding the push button start switch (without the brake pedal applied) for 5 s will place the vehicle in run/start mode (without the vehicle running) and the green LED (Run/Start) will illuminate. With the ignition off (with the brake pedal applied), pressing the ignition mode switch button once, the vehicle will enter run/start mode and the green LED (run/start) will illuminate. This will start the engine. Both LEDs have the voltage supplied from the body control module.


There should be a data PID for the mode switch...should show system voltage and when the start button is pushed the voltage should change.

 

@C5 Diag thank you for the posts. This is my personal car which is used mostly for HPDE on the track. I think you are on the right track but I'd like to refine the direction a bit. The starter is just one of the symptoms. The first drawing you posted, right at the top shows "hot with ignition main relay energized." The problem is that the relay does not energize unless you hold the starter button for 5 seconds. There are multiple systems that do not work without that relay, including the outer instrument cluster gauges. All those systems are dead until you hold the starter button.

The curious thing is that the electric hatch release also does not work until the main relay engages. The hatch does not work with either the key fob or the button on the dash. That feature should work even with the key off.

I'm looking for what those two systems have in common. I'm guessing a ground, one that maybe feeds back through the main relay after we force it to engage. All these symptoms came on at one exact time. it was not intermittent before that time.

 

First did your Techs scan for trouble codes especially in the BCM or any “U” or communication codes ??…as far as your hatch it is not a hatch circuit from 50 years ago…the hatch has its own module as you can see in the 2nd wiring diagram and communicates over the low speed or serial data network…if the button or FOB is used that sends a serial data signal from the FOB to the RCDLR to the BCM and then to the liftgate module…with the button it sends a signal to the BCM and then to the Liftgate Control Module to open the hatch…the BCM is also the Power Mode Master if you read the verbiage and controls what happens when you push the start button…your Techs are going to have to go into the BCM with the scan tool to look at the Power Mode section and see what happens when the accy mode, or run/start modes are selected…this may also be an “Ignition Mode Switch” issue…my last 2 screenshots show the data PID before I push the start button and you can see the voltage is 11.57 volts(my battery voltage is 12.5) because if you look at the switch it goes through 1 resistor and when you push the start button it goes through the 2nd resistor and the voltage reads 5.82 with start button pushed…power for the start button comes from the BCM if you look at the wiring diagram…you may have a bad start switch or a bad ECM…I would look at all the BCM powers and grounds also…you can pass this along to your Techs and the GM Engineers…I’m just a shade tree mechanic.

** Since you have issues with just the trunk release and no other modules just go disconnect that module and see if the car starts again…that module is on the serial data bus and may be affecting the BCM…with a communication issue that is sometimes what you have to do is start disconnecting modules !!..an issue like yours is not a blown fuse so you need a very skilled electrical Tech…I can recommend a good diagnostic guy in Avoca NY and I think that’s about an hour from you…South Main Auto.

 

When you press the start button you should see “Run/Crank Relay Command” — ON and Current Power Mode— CRANK REQUEST !!

 

If the Ignition Main Relay is not energized you can see the voltage that activates the control side of the relay (85) comes from the BCM…see if you have 12 volts there…ground G100 should be checked…you can see your issue may be BCM related…to get the relay to function you can take some thin copper wire and wrap it around pin 85 blade and reinstall the relay…apply 12 volts to the copper wire and the relay should work.