98 Jeep Grand Cherokee V6 4.0L with P0320 and P1391: Crankshaft Sensor Failure Diagnosis

The P0320 code is actually a generic OBD-II code that points specifically to the crankshaft position sensor — not the cam. The P1391 is Chrysler-specific and can indicate either the cam or crank sensor, but in this case, given the symptoms, it's more likely related to the crankshaft sensor. A high-quality Chrysler OEM crankshaft sensor is recommended for reliability; aftermarket parts often fail sooner. Make sure you're using a genuine part from Chrysler or Mopar.

I replaced the crankshaft sensor, but now the vehicle won't start at all — it cranks over but doesn’t ignite. Should I try replacing the camshaft sensor next? It seems like that might be the root cause given the symptoms.

This sounds odd — does my 1998 Jeep Grand Cherokee even have a separate camshaft sensor? I can't find one in any diagrams. With these codes, it seems like either the cam or crank sensor should be at fault. Could it be something else, like the throttle position sensor (TPS)? The car cranks but won’t start — that doesn’t seem to point directly to TPS.

The camshaft sensor is actually part of the distributor assembly and is unlikely to be the source here. P0320 specifically refers to the crankshaft position sensor, not the cam. A faulty throttle position sensor (TPS) wouldn’t prevent starting or spark — only affect idle or performance. The crankshaft sensor, however, directly controls engine timing and ignition. If it fails, the engine won't start at all. I recommend checking for power to the sensor, verifying fuse status (especially the ASD fuse), and using a signal scope to confirm proper sensor output. Did you use a Mopar or OEM part? Also, ensure the wiring is intact — even a loose connection can cause this issue.

Thanks for the help! I’ll check power to the crankshaft sensor and inspect all fuses. The issue started while driving down the street — it just shut off suddenly. Since then, I haven’t been able to start it again. I’ll verify everything and update once I have more results.

Now that I think about it, my sister took the Jeep in for a transmission service — she said there was a slipping issue. Could that work have caused something to go wrong? Maybe they loosened or damaged a sensor or wiring harness?

That’s possible. Before replacing any sensors, double-check all ignition wires to ensure they’re properly installed and connected to the correct cylinders. What was the original reason for the transmission service? If there were no prior symptoms, I’d recommend contacting the shop that performed it to verify their work. Also, what brand of crankshaft sensor did you install? OEM parts tend to perform better than generic aftermarket ones.

Here’s what happened: it's my sister’s Jeep. She took it in because her transmission was slipping — no tune-up was done. The shop fixed the issue, possibly by flushing the transmission fluid. I drove it for about three hours that night and it ran fine. The next day, I drove to work and during lunchtime, while driving, it just shut off. I replaced the crankshaft sensor with a dealer OEM part. I’ll recheck all wiring connections — it seems like something might have been disturbed or left loose during the transmission repair. I’ll also check if the flywheel is properly aligned or damaged. Thanks for your help!

The weird thing is that the check engine light wasn’t on at all — not even after the incident. But when I plugged in my OBD2 scanner, it picked up both P0320 and P1391 codes. That’s how I discovered them.

If the transmission was removed or serviced, there's a real possibility that the crankshaft sensor wiring was damaged or the flywheel position is off. The flywheel could be misaligned or even cracked — this can cause ignition failure and sensor errors. There are several potential scenarios here.

Thanks, Jeff! I’ve confirmed power to all circuits and no blown fuses. I’m going back to the shop that worked on the transmission to see if they can diagnose or fix it — as you mentioned, there are many possible causes now. I’ll update once I get a resolution.

ECU or PCM replacement might be necessary — though I don’t understand how the car would just shut off like that. Still, thanks for the insight, Jeff!

Is it the ECU or the PCM? These are often used interchangeably in older Jeep models, but they’re different components — which one should be replaced if the sensor circuit is faulty?