Starting issues C6
- Thread starter Milanm10
- Start date
teamzr1
Supporting vendor
OK, so it is not a VATS/security issue preventing starter being commanded on
Also, then the PCM needs to see that the park/neutral switch is in those positions
If the switch is out of alignment, or switch itself at fault or wiring for it
With key on, and if you move, the shifter, does the dash or DIC show gear changes ?
Does "SHIFT TO PARK" show up on the DIC when you shift into a gear ?
Does the C6 require the brake pedal be stepped on to be started ?
Have you checked for any blown fuses ?
You say battery looks OK, does a meter show at least 12.5 volts ?
Can you measure at starter to see what voltage is there ?
With D/C meter connected and attempt to start, does the voltage drop at all ?
How old is the battery and has the car sat for some time not being used as a battery can show voltage
but has weak cells that cannot handle the current load of starter, so do you have a charger to put on battery
and see if any changes ?
Also, then the PCM needs to see that the park/neutral switch is in those positions
If the switch is out of alignment, or switch itself at fault or wiring for it
With key on, and if you move, the shifter, does the dash or DIC show gear changes ?
Does "SHIFT TO PARK" show up on the DIC when you shift into a gear ?
Does the C6 require the brake pedal be stepped on to be started ?
Have you checked for any blown fuses ?
You say battery looks OK, does a meter show at least 12.5 volts ?
Can you measure at starter to see what voltage is there ?
With D/C meter connected and attempt to start, does the voltage drop at all ?
How old is the battery and has the car sat for some time not being used as a battery can show voltage
but has weak cells that cannot handle the current load of starter, so do you have a charger to put on battery
and see if any changes ?
Last edited:
teamzr1
Supporting vendor
When the ignition mode switch is placed in the START position, a discrete input is sent to the body control module (BCM) notifying it that engine start has been requested.
The BCM then verifies that the brake pedal has been depressed with a discrete input from the brake pedal position sensor and that the key fob, with the correct code, is in the vehicle.
After this information has been verified the BCM grounds the control side of the RUN/CRANK Relay closing the switch side of it and allowing battery positive voltage to flow from the BATT 3 fuse through the RUN/CRANK Relay switch, PCM fuse to the battery positive voltage side of the CRANK relay coil.
The BCM also sends a high speed GMLAN message to the PCM requesting engine start.
The ECM will then verify that the internal mode switch (IMS) is in Park / Neutral.
After this has been verified the PCM grounds the control circuit of the CRANK relay closing the CRANK relay switch circuit and allowing battery positive voltage to flow through the STARTER fuse, the CRANK relay switch to the S terminal of the Starter solenoid cranking the engine. Ground is supplied through the engine block.
That means the brake safety switch could also be the problem
Also, the relay for the starter could be the issue, find that one and at the top is the part number, you will find other relays with same part number
so for a test, you could swap the starter relay with another and test that
The BCM then verifies that the brake pedal has been depressed with a discrete input from the brake pedal position sensor and that the key fob, with the correct code, is in the vehicle.
After this information has been verified the BCM grounds the control side of the RUN/CRANK Relay closing the switch side of it and allowing battery positive voltage to flow from the BATT 3 fuse through the RUN/CRANK Relay switch, PCM fuse to the battery positive voltage side of the CRANK relay coil.
The BCM also sends a high speed GMLAN message to the PCM requesting engine start.
The ECM will then verify that the internal mode switch (IMS) is in Park / Neutral.
After this has been verified the PCM grounds the control circuit of the CRANK relay closing the CRANK relay switch circuit and allowing battery positive voltage to flow through the STARTER fuse, the CRANK relay switch to the S terminal of the Starter solenoid cranking the engine. Ground is supplied through the engine block.
That means the brake safety switch could also be the problem
Also, the relay for the starter could be the issue, find that one and at the top is the part number, you will find other relays with same part number
so for a test, you could swap the starter relay with another and test that
teamzr1
Supporting vendor
Shifter assembly showing the lever in park.
Hence shifter has front contact switches that tells the BCM that the BCM is in park when the lever is all the way forward. To see if the lever contact switch needs to be adjusted, then just push the lever hard forward when you try to start the car, and if this starts the car, then will need to adjust the micro switch lever.
The second one is that you have to have your foot on the brake pedal, pushing it down.
Tech II or OBDII scanner will make short work of this, since you can go into BCM data to make sure that the brake pedal sensor is working correctly, if not, then do a BPS relearn if the U of the switch has worn instead.
Hence, Brake pedal switch is not a on/off type switch, but a resistance switch that are not the same from switch to switch. So car needs to first lean the pedal not touched resistance, then pedal pressed down resistance next.
To see if the pedal needs a relearn or replacement with relearn, push the lower side of the starter button for 5 seconds to get the car into run mode/motor off, press the brake pedal down the normal amount that you are when starting the car and have someone see if the brake lights are coming on.
Hence if dials are sweeping, then BCM does have the car in run mode to start with (why you can jump the relay and car starts), but waiting on the Brake pedal push with trans in park conformation. Before it going to send the signal for the relay to spin the starter.
And yes, if you replace the brake pedal sensor, will need to do a BPS relearn of the sensor to the car. The pedal untouched is easy to program in since you don't touch it, while when you do the pedal press to program that in, only press the pedal enough to just lightly get into the brakes, since you're not going to be two footing the pedal to start the car.
As for the run crank relay on the BCM, it's on the bottom side of the module with the back-up lights relay if the tech II is both showing that the trans is in park, and the brake is being pushed enough for the BCM, but the relay is still not firing.
Hence shifter has front contact switches that tells the BCM that the BCM is in park when the lever is all the way forward. To see if the lever contact switch needs to be adjusted, then just push the lever hard forward when you try to start the car, and if this starts the car, then will need to adjust the micro switch lever.
The second one is that you have to have your foot on the brake pedal, pushing it down.
Tech II or OBDII scanner will make short work of this, since you can go into BCM data to make sure that the brake pedal sensor is working correctly, if not, then do a BPS relearn if the U of the switch has worn instead.
Hence, Brake pedal switch is not a on/off type switch, but a resistance switch that are not the same from switch to switch. So car needs to first lean the pedal not touched resistance, then pedal pressed down resistance next.
To see if the pedal needs a relearn or replacement with relearn, push the lower side of the starter button for 5 seconds to get the car into run mode/motor off, press the brake pedal down the normal amount that you are when starting the car and have someone see if the brake lights are coming on.
Hence if dials are sweeping, then BCM does have the car in run mode to start with (why you can jump the relay and car starts), but waiting on the Brake pedal push with trans in park conformation. Before it going to send the signal for the relay to spin the starter.
And yes, if you replace the brake pedal sensor, will need to do a BPS relearn of the sensor to the car. The pedal untouched is easy to program in since you don't touch it, while when you do the pedal press to program that in, only press the pedal enough to just lightly get into the brakes, since you're not going to be two footing the pedal to start the car.
As for the run crank relay on the BCM, it's on the bottom side of the module with the back-up lights relay if the tech II is both showing that the trans is in park, and the brake is being pushed enough for the BCM, but the relay is still not firing.
