I have a no crank no start condition. This is an 06 LSJ SS/SC. I narrowed it down to the crank relay, this is what i know:

1) When using key to request crank and while crank relay is out, bridging pins 30 and 87 with wire, car starts right up.
2) When key is requesting crank and testing pin 85 and 86 with multimeter it shows 12v
3) When key is requesting crank and testing pin 85 and 86 with Test light, Test light lights up for like .1 seconds and then goes out
4) When key is requesting crank and testing pin 86 against chasis ground with test light, i get a sustained full bright light.
5) When key is requesting crank and testing pin 85 against +12v battery post with test light, light blinks once and goes out.

This points to a bad ground for pin 85. I think this ground is G101 from what i gathered from the service manuals. but also seems it goes to the ECM and Starter as well. Where is G101, and what other grounds should i check if any?

Thanks in advance!

 

I assume you don't have a check engine light or security light?

 

Nope. I bought a new ecm and currently I haven't performed the crankshaft relearn so I have that code but thats the only one. I switched back to my old ecm which has no codes and same issue.

 

Upon closer inspection of the fuse box harness blocks it appears one of the pins (2nd pin) is burnt. The pin next door (3rd pin) is connected to the ground on the starter relay. May be related, will report back more info later...

 

Turns out the burnt pin is rear defogger 12v supply pin. Defogger window wart has been hanging for sometime. I will worry about this at a later date. I buttoned up the fuse box and tested the resistance between ECM C1 pin 48 (starter relay ground) and pin 85 at the starter relay location. I get .4 ohms. Ecm must be turning off ground on me due to something else.

 

I have pulled the cover off my crank/start relay and witnessed it not closing the circuit. With a test lamp across pins 85 and 86 i now get a constant solid light. I tried pitting a multimeter across the same pins when cranking and get 11.5v. While cranking i physically close the pins and it starts right up. I should add this is an intermittent crank issue. I have a brand new relay i have tested that i have tried as well as i have tested the open relay in other circuits and it operates fine. Do i have the relay in backwards? When cranking i have 12V on pin 86 and ground on pin 85.

Whenever I ground pin 85 my car starts. What would cause this pin to have a faulty ground?

 

It was a bent pin on the circuit board in the fuse box!