I took the IPM (integrated power module, aka the fuse box) apart, cleaned all its connections, re-electrical taped everything, and put it all back together. No change in weird electrical behavior.
But I was able to pull codes using Torque. I got:
Torque lists this as: Powertrain – powertrain induced chassis pitch output circuit
but the Chrysler-specific description for this code is “J1850 Communication Bus.”
Torque lists this as: Powertrain ( 1) ECM/PCM power input signal intermittent
This is an industry-wide description and the manufacturer doesn’t matter.
So the ECM confirms that there’s a problem with the bus communication. I’m guessing that’s the symptom, rather than the cause — the cause is that the ECM or PCM isn’t getting reliable power.
Here’s some info about P2509:
P2509-POWERDOWN DATA LOST ERROR
Continuous – Key on or Key off.
Loss of voltage detected at the ECM for a calibrated amount of time.
* Poor connections at the batteries
* Low battery voltage
* Open fused B+ To ECM
* Open ground circuit
* Battery + shorted to other circuits
* Return circuit shorted
* Battery + shorted to ground
* Intermittent condition
And this is certainly interesting:
Case Number K24612402
Vehicle Issue MIL. P2509. The engine may stumble or stall out.;12 volt power (unswitched) and the ground circuits to the ECM are good. Batteries and charging system operation are good. If applicable (2006 and 2007 MY trucks), the ECM has already been updated per TSB 18-001-07.
System or Component Die out / Stall,Hesitation / Sag / Stumble;DTC / Error Message;ECM
Recommendation If the problem can be duplicated, disconnect the fan clutch 6-way connector and check if the concern still occurs. If the problem no longer occurs, replace the fan clutch assembly.
Case Number K13878564
Vehicle Issue Engine Stalls Out. ‘NO BUS’ Message Is Displayed. P1652.;Power and ground connections to the Cummins ECM are good. P1652 and P2509 are set.
System or Component Die out / Stall;DTC / Error Message;Electronic Control Module,ECM;Yes – Intermittent,Yes – Continuously
Recommendation Inspect the wiring harness near the C108 (14 pin) connector. This connector should be at the back of the engine, near the transmission bell housing.
The combination of both P1652 and P2509, and the fact that they’re both correlated with that wiring harness near the transmission bellhousing, makes me think I really need to have a look at that. I also need to take a closer look at the radio harness to make sure it’s not grounding out at all.