One day the car started, the next day, it did not even try to crank. All interior accessories work. The accessories go off (as designed) when the key it turned to crank
The battery is new and fully charged, the vehicle has 167,000 miles on it
I have confirmed all of the following are good:
starter relay
starter relay fuse
run/crank relay
run/crank relay fuse
engine control relay
engine control relay fuse
80A fuse at battery
200A fuse at starter
12V at starter
ground at starter
starter and starter solenoid
The original timing chain is still there but I read it can last up to 300K miles
The cam position sensor was replaced about a year ago.
I am down to suspecting either PCM/ECM or a broken wire in the main fuse box (although I haven't experienced any intermittent start failures) don't really know how to troubleshoot the PCM/ECM. Please help!
Since the engine does not even try to rollover, I have not yet considered spark or fuel.
Starter System Description:
When the ignition switch is placed in the START position, a (voltage) signal is supplied to the body control module (BCM) notifying it that the ignition is in the START position.
The BCM then sends a serial data message to the engine control module (ECM) that crank has been requested. The ECM then verifies that the clutch is fully depressed or the automatic transmission is in Park/Neutral.
If it is, the ECM then supplies 12 V to the control circuit of the starter relay. When this occurs, battery voltage is supplied through the switch of the starter relay to the starter solenoid.
With a system that uses switches, voltage signals, and communication networks between computer modules, the best way to troubleshoot it is with a scanner.
You can do an Auto Scan to see if there are codes set in any of these modules which can point you to the issue.
Possibly a communication code or a code for another component.
In the case of your Terrain, by the system description you'd want to see if the BCM is getting the voltage signal from the ignition switch, if the BCM is able to communicate the "crank request" to the ECM over the communication network, and if the ECM is getting the voltage signal from the Transmission Internal Mode Switch (to let the ECM know the transmission is in Park or Neutral so it provides the 12 volts to the control circuit of the starter relay.
Anyway, here's the setup. You can follow the system description through the circuits on the wiring diagram. If you want you can pull the Starter Relay and grab a test light to make sure you have:
Battery voltage on relay socket 30 at all times.
12 volts +or- on relay socket 85 when the key is held in the Start position
Ground on relay socket 86.
Once you establish the relay sockets you can also use a paperclip to "jump" relay sockets 30 and 87 to see if the starter works to confirm that everything on the "Load Side" of the starter circuit and the starter are good.
If you aren't getting 12 volts on relay socket 85 when the key is in "START" then a good scanner will be the way to go to diagnose the problem.
And I wouldn't suspect the ECM/BCM. I'd suspect a wiring issue or an issue with the Transmission Internal Mode Switch or maybe even the ignition switch .
not sure about you guys, but the image doesn't show up for me. I've switched to using imgspice.com for image hosting.
What happens when you turn the key. Is there any clicking? Try whacking the starter. It might be fried.
When I turn the key, I hear the internal relay click on the passenger side. I think that is the one that disengages accessories during starting. I also confirmed that the starter relay, the run/control and engine control relay all click with ignition switch operation. I removed the starter and had it load tested to assure there is nothing wrong with it. But it does not crank and there is no indication that the starter is engaging and there is not a significant dimming any lights as if there was a large starting load. Even though I confirmed the starter relay was good, I removed it and jumpered terminals 30 -86, but it had no effect. Since the relay was working, I didn't think it would matter. Since there are lots of seemingly unrelated paths, I actually tested ever one of the relays and inspected every fuse as well as assuring each had continuity when tested with an ohm meter.
how is the engine ground strap?
@wolfman Jump relay sockets 30 & 87, NOT relay sockets 30 and 86
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If you have power on relay socket 30, and jumping relay sockets 30 & 87 doesn't make the starter work, go down to the starter and check for power on starter wiring terminal "S" (the small wire going to the starter from relay socket 87) while you have a paper clip jumping relay sockets 30 & 87
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If you don't have power there, refer to the wiring diagram
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Power goes from relay socket 87 through fuse F9 in the underhood fuse box on its way to the "S" terminal of the starter. Make sure you have power on one of the fuse 9 sockets when relay sockets 30 & 87 are jumped. If you do, try replacing that fuse. If that doesn't work, look for a wiring problem between that fuse and the "S" terminal of the starter