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1999 Jeep Grand Cherokee 4.7L - P1391 Code After Replacing Cam and Crank Sensors with OEM Mopar Parts

Model: 1999 jeep grand cherokee Fault Code: P1391 Posted: 2018-06-23 14:24

I'm experiencing a P1391 code on my 1999 Jeep Grand Cherokee 4.7L. I recently replaced both the camshaft and crankshaft position sensors with OEM Mopar components, and I also replaced the Powertrain Control Module (PCM) due to previous idle issues. Despite these upgrades, the P1391 code is still appearing. Could a timing issue be causing this? Or are there other possible causes related to sensor signals or wiring? The P1391 diagnostic trouble code indicates an intermittent loss of signal from either the Cam Position (CMP) or Crank Position (CKP) sensors. I want to confirm whether my timing setup is correct, or if another factor—such as sensor wiring, harness connections, or sync issues—is responsible.

Related fault codes

P1391

Comments (2)

Anonymous 2018-06-23 15:36

Are there any additional symptoms besides the check engine light and P1391 code? While timing can trigger this issue, several other scenarios—such as wiring faults or sensor signal degradation—can also cause it. A thorough diagnosis is needed to pinpoint the root cause.

Anonymous 2018-06-25 10:47

Jeep vehicles are not particularly difficult to troubleshoot—but you must use a proper scanner with a key to access all stored codes. Make sure you're only seeing one code (P1391), as multiple codes may indicate deeper issues. Important: The P1391 code does not directly instruct you to replace a part. It indicates an intermittent loss of signal from the CMP or CKP sensors. To diagnose properly, use a graphing scanner to check sensor sync and review freeze frame data. Then examine the CMP and CKP signals visually on the waveform. Next steps: Gently wiggle or tug the sensor harnesses while the engine is running—any drop in signal may point to a loose connection or damaged wiring. Confirm whether the sensors are properly synchronized, if one sensor is faulty, or if there's an issue with the wiring harness.