Once it turned colder, the dash gauges started acting up again, going dead, lights flashing, etc. I was getting codes P0480 and P0483.
I made a weather front out of a cardboard box and put it between the radiator and the condenser, and disconnected the fan clutch.
Disconnecting it made no difference. Everything is still going crazy. So, at least I can be reasonably confident there’s nothing wrong with the fan clutch; that’s $350 I don’t need to spend.
And this morning I got the code P1652, indicating the J1850 bus is shorting to ground somewhere.
pwong on the Cummins Forum linked a diagnostic procedure for this code that should isolate it from a bad ECM. Either the problem is caused by a bad ECM, or by a short elsewhere (or possibly in another module that is connected to the ECM via the J1850 bus).
I hope it’s not the ECM; they’re not a cheap replacement.
The steps are:
- Eliminate the ECM as a source of the problem.
- Eliminate wiring shorts as a source of the problem.
- Eliminate every module connected to the bus as a source of the problem (by unplugging all modules and then plugging each one back in, one at a time, until the problem recurs).
The upshot is that I have to go through the entire engine compartment, checking all the wiring and modules, one-by-one. Hopefully I can find something obviously wrong.