2002 Dodge Durango Code P1391: Intermittent Crank/Cam Sensor Loss Fix & Diagnosis
Hello! I'm seeking help with a recurring Check Engine Light issue on my 2002 Dodge Durango (5.9L 408 Mopar engine). The vehicle is showing intermittent P1391 code — 'Intermittent Loss of Crankshaft or Camshaft Position Sensor Signal'. I've replaced both the crank and cam sensors with new units, and both have been synced to zero via an OBD2 scanner. Despite this, the P1391 code returns intermittently—appearing during about 1 in every 15 starts—and the engine runs rough initially before stabilizing. Voltage readings from the sensor pigtail are stable at 5.14V with consistent grounding. No fluctuations have been observed. The issue persists even after clearing the code, which reappears over time. I'm looking for a clear diagnostic path to identify whether this is a wiring harness fault, sensor installation issue, or a problem within the Powertrain Control Module (PCM). I suspect the PCM may be 'hanging' on the error due to intermittent signal loss—similar to how computers can freeze—but I need confirmation. I'm also curious: could a misfire from ignition components (e.g., coil, distributor) or timing chain issues cause this code? The truck has original 360 distributor and flywheel. Timing is confirmed accurate. Any advice on affordable OBD2 scanners that allow real-time monitoring of crank/cam signals during symptoms would be greatly appreciated—especially since dealerships like Snap-On push high-end tools that exceed the vehicle's value. Additional note: I recently had a local electrical shop in Orlando test the sensors and wiring. They confirmed both sensors were functional and the wiring harness was intact, but reported intermittent 'loss of signal' to the PCM. Based on this, they concluded the PCM was faulty—leading me to purchase a new OEM Mopar PCM from an Orlando Dodge dealer, which was flashed with VIN data and tuned for 408 engine operation. Unfortunately, the P1391 code returned after reflash. I'm now considering further diagnostics such as distributor gear seizure or ignition advance issues. A recent $46 test ruled out coil failure. I've also learned that the Check Engine Light must be physically present in the dash cluster—otherwise, OBD2 scanners won't allow access to fuel sync adjustments. Our original unit was missing; it was replaced with a soldered LED bulb for just $2 instead of $599 at dealership. Final fix (for 408 Mopar engines): 1. Ensure the Check Engine Light is active—without it, no deeper diagnostics are possible. 2. Advance fuel timing by rotating distributor (small increments, ~1/16 inch) to +6 degrees; this improves engine stability on modified motors. 3. Modify the crankshaft position sensor: remove the rubber dust grommet and grind the hole in the sensor housing into a slot so it can be shifted toward the distributor side—ensuring physical contact with the distributor end. 4. Recheck fuel sync at +6 after modification. This solution resolved the P1391 issue for our 2002 Durango with a 408 Mopar engine. If you're doing a similar build, this may save significant time and cost.
The intermittent loss of crank or cam sensor signals could point to a wiring harness issue. When symptoms occur, use an oscilloscope to monitor the actual crank and cam signal waveforms for out-of-range readings.