I'm helping out a friend a customers car turned over. The starter won't click when using the starter button.

We pulled the fuse for the starter (#43) and it checked out ok.

We pulled the lead wire/harness to the starter and feed it direct power, the starter turns over with the motor.

Plenty of battery voltage.

Now, plug the lead harness back in and nothing. We looked for damage to the wire (LT headers) and some of it was singed. We tested the lead behind the damage and nothing, no voltage when ignition/run is engaged.

The car has power as the battery is good.

Also, oddly enough, we checked the fuse panel where the starter fuse goes and we couldn't get a read. Not sure on that.

Thanks.

The motor turns over fine but only when we feed it direct power, again, to the lead harness port.

 

So you are saying that if you put an external +12v to the starter it will crank. But you do not get +12volts to the starter when using the start button on the dash.

Is this car a stick? Have you tried checking the clutch switch?

The system is not straight forward like older vehicles.

When you press the start button, this analog signal is read by the BCM.
Then the BCM activates the run/crank relay (# 7) If the fob is seen.
The BCM notifies the ECM that the start function has been requested via the GM lan.
The ecm then checks the clutch switch input and then activates the crank relay (#43).
When this is successful, the +12volts from fuse #30 is sent to the starter solenoid via relay #43. Contact C14 on the crank relay should be hot, A13 will be hot when the relay is activated.

DJ

 

much appreciated.

No, the car is an auto. I'm thinking the lead wire is just fried. There was a good spot where the wire was singed and we tested the wire behind for a signal. Nothing when set to run.

We're gonna add a new wire and see what happens. The relays/fuses are clicking but the starter is not.

 

Well... looked over the car yesterday night. Still cannot get it to crank on it's own. We're going to review it all over again. We checked all of the grounds, no issues there.

Will report back.

 

Have you tried to pull the crank relay (#43) and jumper across terminals C14 and A13? This should allow you to crank if Fuse #40 is good along with the wiring.

DJ

 

Will give that a try, thanks.

Will report back.

 

we swapped out relays which were known to be working and that didn't work. All the wiring and grounds seem in order. Are there any sensors which might be messing with us?

Next step would be to remove the starter and check the terminals though they seem to be fine from what we can see with it mounted on the block.

The battery allegedly has 1000 cranking amps (per advance auto parts check the morning before) or else I'd replace it.

What I'd really like is a diagram (with wire colors) that traces the power from the battery to the switch, relay, fuse, starter. That way we can trace the cable from start to finish and diagnose if there is a broken wire in the loom.

 

Also, wouldn't mind knowing which way the relay needs to face and whether or not that matters.

 

we followed your suggestion and jumped it and it works! Thanks! We are en route to get another relay... if that's not it what else do you think it could be?

Thanks again!

 

purchased new relays... that didn't do it.

This is driving me

 

also the bypass cranks the starter and the engine but even with a manual boot of the starter the engine will not turn over and it is getting fuel pressure.

 

I will PM you, but by doing this test we can rule out quite a bit. I am sure I can help you diagnose this.

DJ

 

So, if we jump the relay (#43) and the starter turns, can we deduce that the before the problem is before the relay, not after it?

Where can we find the # 7 run/crank Relay?

 

Okay, so... here's a brief run down of what has been done in case anyone has any previous experience dealing with anything similar to this. Also, the HP Tuners will say it's connected to the car, but won't allow us to see anything and the scan tools we have don't connect.

Replaced the battery - Nothing
Jumped under hood relay - Car cranked
Checked under hood fuses - Every single one okay
Checked Passenger kick panel and grounded the Run/Crank Relay - Fuel Pumps Primed. (Don't think it cranked though)
Checked for 12v at the obd2 (PIN 16) - 12v is there
Checked pin 5 on the obd2 for ground - there is less than 1 ohm resistance to ground with the battery out... With the battery in I get 18.5 ohms and then after a while of it sitting it will start to decrease and fluctuate all over the place... Odd
Yanked out the Automatic transmission's wiring plug and traced the wire that sends the park/neutral signal (pin 3 -orange/black) to the ECM - Signal seems fine, it increases in voltage when in park or neutral.
Replaced ECM with one that has my Vin and bypasses the VAT (Vehicle's Anti-theft) - Nothing, still in the same boat.

:will y:

I'd like to note that DJ has really helped out. I really have to thank him. We've spent hours on the phone together learning how this stupid car works from an electrical engineer's standpoint. The problem is that GM made the wiring on this car so asinine and connected one circuit on top of other circuits that share grounds and erratically starts to communicate through the GM lan, which has no diagrams, and the diagrams that GM gives you are basically a Pandora's box of crap with horrible pictures.

With that being said, the car does have a ton of electrical things in it which require signal/power... Though I don't believe any of them caused this problem because the were working fine before, I figure it's worth mentioning. The things I can remember off the top of my head are as follows: Aeromotive A1400 pump, methanol, nitrous, a MicroEdge nitrous controller, Nexus gauges, Head unit and a partridge in a pear tree... We took out the turbos, put in a blower and now I have this BS electrical Gremlin... any help would be greatly appreciated!

 

Did I miss the part where you checked the brake switch? Later! Frank

 

I read about that last night on another forum. Do you know where that switch is, where it goes, and what color the wires coming out of it are?

 

Ok, the brake lights work so the BCM is getting the correct signal from it. This is the same signal that the BCM uses to tell the ignition that you have the brake applied.

Also just to note, we checked all the chassis grounds.