Hi. I'm trying to pinpoint an error. When I attempted to start my car the other day, it failed to start quickly, and the odometer showed no bus. Whar would cause this error?

 

any number of things wire issue power issue one of the computers having an issue.

 

Check powers and grounds to PCM, and check 5v supply for a short to ground.

Faulty PCM, Loss of power or ground, Shorted Crank sensor, shorted Cam sensor Shorted Tps, Shorted Map....Will all cause NoBuS.

The power and grounds are simple...grab a wiring diagram or Pinout chart for PCM. 1 battery feed , one ignition feed, two grounds.

With a Voltmeter on 20vdc scale, check for 5v at TPS connector (Usually The easiest to get to, But any of the mentioned connectors will work). If unplugging it restores Communication...replace it. If there is no voltage (5V)...unplug each of the others one at a time, until the voltage returns.... The last one you unplugged is the culprit and must be replaced.

 

Thanks for the info, that's more than I've been able to find elsewhere.

Is there any tool or way to find out which computer might be having issues or is it just running through all the wires as Djinn-n-Tonic said?

Let me just share a little bit more information about the issue (since it is a little late and dark to try things out).

This has only happened once. I've successfully started the vehicle on multiple occasions since this occurred, though I have not kept it running for very long. Correct me if I'm wrong, but I've also been running a system check by holding the Odo reset and turning the ignition to 'on'. Supposedly (from what I've heard) that will check the bus connection (and OBDII error codes). I haven't seen anything which would leave me to believe any errors are occurring.

Thanks.

 

that is a Cluster test only.


Problem here......Unless you are having an issue at THIS PRECISE MOMENT.....You are Chasing a GHOST.....

Also.....Unless you have access to a Factory scan tool.... You will be chasing down Wiring...Generic OBD scanners arent nearly powerful enough to access what you are looking for.

The next step,after you have eliminated PCM Functioning correctly is PCI and SCI communications...but we'll go there when we have to, to avoid the confusion.

 

Well that makes me feel silly.


Is any sort of stress test to possibly recreate the error, or possibly show any related errors?

Also, would something like this help track down any wiring problems?

Sounds like a plan.

 

It shouldnt...You arent the first and wont be the last.

As for Tools like that...Save Your money...There would have to be an existing short or open circuit for that to do anything of benefit..

Stressing the system........I usually check powers and grounds with one of two tools......

An Old wiper motor that has been laying around the shop, Or an Old T3 Sealed beam headlamp with wires soldered to the terminals.....With "LOADS" like that, Im 100% sure there is NO VOLTAGE DROP on the circuit I'm checking.

Bus Problems usually are extremely intermittent, progressing to Un reliable, then to annoying, then Finally to BROKEN.....But I've NEVER seen one fix itself.....So it will eventually become apparent.

I have one in the shop right now, that I have put thru almost 400 miles of road tests...and it dropped dead pulling out of the service bay this morning......