I posted before as my 05 base will not crank when push button is used, if I jump the crank relay it cranks and starts right up and runs and drives awesome and every thing works as it should. Any advise as to what to try, previous owner replace the upper fuse box as dealer said that would fix it but no dice. Any suggestions would be greatly appreciated. I have just replaced the battery and cables and cleaned all the connections including the grounds to the frame.
I have built alot of c2 cars and on my drivers I use a jumper wire on the starter from the positive stud to the start hub, with a push button under the dash to help from the passer by stealing the car as alot of the old chevy's will start with about any key. Would this be okay to do on the 05. This is my first time having a electronics car so learning on the fly so to say. Thanks

 

I forgot to mention that the digital readout and the sweep gauge both say 11.9 volts but when I test the battery it is 12.65 volts

 

The starter button can go bad. Have you replaced it?

 

No I have not but once in a while it will start on its own, plus when I push the button everything else does what it is supposed to. So thought at least the switch is still good but maybe not.

 

If, when you push the button, everything seems to start happening except no crank, then I would also not suspect the button.

 

If the engine consistently cranks with the crank relay being jumped we can take the load side of the starting circuit out of the picture...having a scan tool that can communicate with all the cars modules would be helpful as this may be a communication issue especially being able to communicate with the BCM ...with a scan tool if you have one I would see what modules you can and can't communicate with....if your car is an automatic did you try starting in neutral ??...if you have a DVOM and a test light there are a few things we can try...the C6's are a little more difficult to diagnose because there is a more "logic" involved in starting.

 

I have a nano scan tool on order but don't have anything but a cheap harbor freight code reader right now that the previous owner gave me when I bought the car. I have tried starting the car with the fob in glove box as well as in neutral and also pushing up on the shifter when in park. When I jump the relay it starts right up and runs and drives great, also all other options and functions work as they should. Has the engine light on but the cheapo scanner says it is a o2 sensor.

 

Prob not the fob - it all turns on and isn’t saying “fob not detected.”

but it could be the neutral safety switch / or whatever they’re called now. Basically whatever tells the computer the car is in park. I’d check that.

 

I have tried moving the shifter to neutral as well as pushed it forward to see if the safety switch was a little wore out, didn't change anything. thanks for the reply

 

With Crank Relay 43 removed take a test light connected to battery NEGATIVE…probe terminal 86 (closest to you and toward the windshield (aft inboard) and DON’T shove the test light in there…use a straight pin if your test light probe is thick...the test light will light for about 10 seconds or so when the start button is pushed…if it lights the load side of the run crank relay and ECM fuse and Park Neutral/Clutch Safety Switch (IMS Mode Switch) are all being energized...also check Batt 3 fuse 26 in the underhood fuse box...it should be "hot" at all times.

 

Thank you for the pic and the diagrams, I will try that on monday when I get back home

 

I tried the test light test and it does not light up, best place to proceed from here? Fuse 26 does have power full time as well

 

I would first make sure the Batt3 and ECM fuses are good...we should go to the run/crank relay at the BCM (on the bottom of it) and jumper terminals 30 and 87 again and see if the car cranks...if it does we at least know that the feed side is good but we don't know if the control side is working...you can try another run/crank relay or test that one with a 12 volt battery and an ohmeter if you know how to do it...as far as the control side it may be better to wait until you get your Nano to look at some inputs that control starting...the brake switch and the IMS Mode switch (park neutral)...you can try the same thing at the run crank relay with the test light connected to ground probing pin 86...try to start the car and see if the test light illuminates...if not what I would do is wrap some thin copper wire around the relay blade 86 and reinstall...what happens is YOU become the ECM ground (run/crank relay control wire) using the test light connected to ground and touching the thin copper wire while trying to start the car...maybe it will just be a bad run/crank relay.

 

Tehc module in bottom of drawing that is located by the trans shifter shaft , have you check it yet.

Conditions for the BCM before it going to send the start.crank command to the ECM, is RCDLR sees the fob for the BCM, BCM sees that your foot in on the brake pedal, TEHC proves that trans in in safe position to start engine, then, BCM will send the run command/crank command to ECM, so ECM can ground the negative side of the starter relay coil in the engine fuse box to send power to the starter solenoid to fire the starter.
Hence tech II in BCM data will show you all these and if they have been meet to get to the crank condition to start with, and well as if the ECM did go into crank mode as well.
If getting run/crank condition in the BCM/ECM data, then need to check 67 yellow/blck wire off the ecm, to make sure its going to a ground condition to fire the engine bay starter relay coil solenoid relay, as well power off the bcm to the positive side of the relay coil, and then power on to the ECM for its ignition 1 control voltage.

As for BCM, have the 15 amp fuse for this side of the math to the engine bay starter relay, as well as the run/crank relay after the fuse on the bottom of the BCM that controls the power out of the BCM to the relay.


So to sum it up since you have a tech II, check to make sure that ECM and BCM are sending the correct controls ones its conditions are meant to begin with.
if they are in the data logging, then its the physical electronics side of the math the problem of why the coil side of the engine bay relay is not being energized to crank the starter.
Note here, ECM should crank the starter for about 5 seconds, then stop energerizing the relay if the engine does not start. That is unless someone went in to the tune and screwed that up isntead. Hence ECM if correct in tune, should be only showing crank for its command for about 5 seconds when data logging once BCM does send it the crank comand.

 

I tried jumping the 87 and 30 position on the bcm relay for run crank and the ignition came on but it did not crank over. Have not tried the test light yet or the thin wire around the relay that you suggested. Thought that since it did not crank jumping the bcm relay it is a communication issue. Is this the fight assumption?

 

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I'm facing exactly the same issue. My ECM is not grounding the Crank Relay under the hood. Car will run like a dream if I provide external ground to the relay.

 

First thing is C4 and C5’s are much easier to diagnose starting issues…LOL !!…you can try jumping 87 and 30 again at the run/crank and with the crank relay removed as you did initially see if the test light illuminates when probing terminal 86 again…we can ground terminal 85 (starter enable control) with the copper wire too and see if it starts…we will see if power gets down from B+ and the BATT3 fuse all the way down to terminal 86…as far as a communication issue they can cause a no crank no start and the first thing you would see is a “no comm” with the car with a scan tool…there are a few checks you can do with a DVOM and the first check will be at the DLC where you hook the scan tool to…with the ohm meter function check between pins 6 and 14…CAN high and low…you should see around 60 ohms (there are 2 each 120 ohm terminating resistors in parallel (BCM and ECM) which if you see 60 the wiring is OK…best to disconnect the battery or wait about 20 minutes till the modules “go to sleep”…also you can check the voltage on 6 and 14…you should see about 2.5 volts (or both add up to 5 volts) in ACC mode or ignition on…using a scope is the BEST way to diagnose these issues but unfortunately very few DIY’ers to include most repair shops and dealerships don’t have or use one…on my scope capture you will see 2 mirror images of CAN high going from 2.5 to 3.5 volts and CAN low from 2.5 down to 1.5 volts…that signal is super fast and my scope is set up to read that signal in MILLIONTHS of a second…maybe best until you get the scan tool to see what’s going on as far as your inputs…do you know if both those relays are good ????

 

Did you figure out what it was ???

 

Yes both the relays are good as I have moved them to other locations and that function worked when I start the car via relay jump. Hoping my scan tool arrives soon, really want to enjoy the car as it runs and drives great once it starts. On my c2 vintage corvettes I use a wire and start button between the Battery terminal and the start terminal on the starter solenoid. I tun the key to run position and then hit the button as about any key will start the older c2's so it is my safety device from the passer by thief. Would this work on my c6 or am I taking a chance at screwing up the computer? I want to get it working correctly but looking at another solution if I cant figure it out. Thanks for your help with this matter

 

Can be made to work with ground wire jumper and switch, if ecm pin 67 is not supplying the needed ground to trigger the relay coil when is suposed to, so long as you do have power to the relay on the coil side, and power to ecm on the pink wire to ecm 19.