Is there a cable issue that causes a no start?

Question

I have a 4x4 12 titan crew cab. Last couple of months I've been battling a no start that I can't seem to diagnose the issue since it's intermittent.

Battery was replaced 6 months ago but for some reason when I turn the key over the truck will not start at times. Everything on the dash lights up as normal, radio comes on, no codes and no blinking lights.

This occurred again last night when I got into the truck, turned the key over and drove 5 blocks to a restaurant. Realized my parking was bad, got back into the truck to correct my parking and turned the key over than it would not start. Had dinner with family for an hour then came back out turned key over and no start. Pressed the brake and moved the shifter from park all the way down to low gear three times with counting in 30 second intervals and on the third attempt truck started.

Drove back home and backed truck into spot. Turned truck off and counted to 30 again and truck fired right up. Got into truck this morning and truck fired right up.

I've been to advanced and a repair shop and when they run tests they say everything is fine, unable to replicate issue, and readouts for starter are normal. Issue occurred after going on a trip that had a bumpy gravel road. I've been under the truck and see nothing jarred or any damage.

I am clueless as to what the issue could be with this truck. Is the issue consistent with a starter going out or since the shifter was manipulated a few times this is a computer that could be going out from the transmission to the starter like a BCM?

narkeleptk · Answer

Forgive me for this sloppy answer but I'm just taking a break from my work. Here is the starting system from the 2010 manual but I think it is the same. Hopefully it helps narrow down which part of the system is failing.

The BCM handles the immobilizer but if this is having issue's you should have current or history DTC's in both the bcm and ecm. Usually issues with bcm are not intermittent either so I would not suspect it.

The bcm will communicate with the fuse box and tell it to send the control signal (ground) to the starter relay once the immobilizer requirements have been satisfied. With your key switch on, use a test light clipped to 12V and probe this terminal. It should light.

The TCM probably sends 12V supply to relay through P/N switch. As long as your in Park or Neutral then you should be able to use your test light clipped to ground and probe this terminal to see it light.

Generally on a relay terminals 85 is ground and 86 is 12V but sometimes its switched up.

With your ignition held in crank you should see 12V on terminal 30 of the relays terminal.

With key switch in ON, You should be able to probe terminal 87 with 12V and your car should start unless there is issue's with starter or its connections.

Is there a cable issue that causes a no start?

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