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1999 Jeep Cherokee P1391 Fault: Intermittent Crankshaft or Camshaft Position Sensor Issue & Diagnostic Tips

Model: 1999 Jeep Cherokee Fault Code: P1391 Posted: 2006-06-21 18:47

I'm experiencing a persistent P1391 fault on my 1999 Jeep Cherokee (2.5L 4-cylinder). The code indicates an intermittent loss of position from either the Crankshaft Position (CKP) or Camshaft Position (CMP) sensor. I've already replaced the CKP sensor and thoroughly inspected, cleaned, and tightened all connectors—including both the sensor and PCM connections. The issue only manifests at startup—after a few seconds, the MIL light activates, and it takes approximately 15–20 seconds for the P1391 code to appear in diagnostics. Notably, I've observed that two consecutive starts are required to trigger the MIL light, after which the vehicle runs normally for hours without any further error logging. This intermittent behavior suggests a timing or sensor alignment issue rather than a hardware failure. The engine is a new long-block replacement with no visible flywheel damage—this supports the idea that the problem lies in sensor signal integrity or mechanical timing. I've tested multiple OBD2 scanners, and Scantool.net (v1.13) provides the most accurate readings, especially for ignition timing. Other tools like Digimoto Lite show inconsistent values (e.g., incorrect timing), which makes them unreliable. Importantly, Scantool detects P1391 even when the MIL light is off—only after repeated starts does it trigger, aligning with my observed pattern. A key point: I cannot reset the P1391 code while the engine is running. The reset must occur after turning off the engine, then initializing the serial interface via the key switch. This behavior appears consistent with older Jeep systems and may be normal for this model. I'm now considering whether the issue stems from a misaligned distributor or worn camshaft sensor teeth—especially given that the original engine had 130,000 miles before failing due to piston damage. I've ruled out crank-to-cam timing errors since the long-block was factory-assembled with proper alignment. I'm planning to test shifting the distributor one tooth forward or backward and will replace it if necessary. Any additional insights on distributor wear, sensor compatibility, or OBD2 reset procedures would be greatly appreciated.

Related fault codes

P1391

Comments (5)

Anonymous 2006-06-22 06:05

Assuming this is a 4.0L 6-cylinder model—though the issue could apply to both engines. Have you tried replacing the camshaft position sensor assembly? Cam sensors fail frequently, especially when drive gear teeth are sharpened due to lack of lubrication or worn distributor bushings. Ensure proper engine timing: either the cam is misaligned with the crank or the distributor is out of phase. Note: Some users refer to Cherokee as 'Cherokee' regardless of whether it's a Grand Cherokee—please confirm your exact engine type for accuracy.

Anonymous 2006-06-22 06:46

Thanks for clarifying—it’s a 1999 Jeep Cherokee with the 2.5L 4-cylinder engine, which makes your advice applicable to both models. I haven’t replaced the camshaft sensor due to unavailability locally and have dismissed it as less likely given the intermittent nature of the fault. Regarding 'timing': ignition timing is managed by the PCM. The CMP (camshaft position sensor) inside the distributor generates pulses only during half a revolution—this means it’s less prone to complete failure than the CKP. If either sensor fails entirely or becomes disconnected, the engine will not start. I have access to both a printed service manual and Alldata (.com). Beyond distributor alignment, no other adjustments are required. Thanks for your input.

Anonymous 2006-06-22 12:33

Great—so it's a 2.5L engine. In short: the distributor is likely either phased incorrectly or the cam-to-crank timing is off. I’m leaning toward a slight distributor misalignment. When setting timing, did you disconnect the coolant temperature sensor? Many Jeep models require this disconnection so the PCM can relearn proper position—similar to Ford’s spout connector procedure. I’ve personally seen many cam sensors go faulty due to sharpened teeth from infrequent oil changes or worn distributor bushings. Also, I’ve had brand-new aftermarket crankshaft sensors fail right out of the box—sometimes due to incorrect air gap at the flywheel. Your cam sensor should be available locally at a dealer or within one day’s shipping distance. Distributors in older 2.2L and 2.5L K-cars are known for intermittent failures and share similar design features. I hope this is just an orientation issue with the distributor rather than a more complex repair. What scanner are you using? Let me know—good luck, and I’ll keep posted! Jeff

Anonymous 2006-06-22 16:04

Excellent insight, Jeff! I’ve been thinking about this all day. I’m going to check the Alldata procedure for distributor replacement instead of relying on my Haynes manual. The original distributor came from an older engine and was installed onto the new long-block. It’s highly unlikely that crank-to-cam timing is off—this was factory-set during assembly, as this is a complete long-block with pre-assembled head. Two possibilities remain: (1) the distributor is misaligned by one tooth. If so, the PCM may be compensating but near its limit—this could explain why startup triggers the error. Or (2) the distributor has worn teeth due to previous engine failure at 130,000 miles when a piston was thrown into the oil pan. I inspected the teeth earlier but may have missed subtle wear. I’ll try shifting the distributor one tooth forward or backward first. If that doesn’t resolve it, I’ll replace the distributor. I’ll update you on results—thank you for your help!

Anonymous 2006-06-26 19:19

Jeff—you're absolutely right! After following Alldata’s procedure (a subscription service worth every penny), I discovered that the distributor was installed at a TDC position 180 degrees off. The alignment holes didn’t line up, so I removed it and used a wooden pin as described in the guide to properly align it. After reassembly, the vehicle started immediately and ran flawlessly with no error codes. It took me nearly a month (the car had been running fine) to diagnose this issue. Initially, I thought it was an intermittent electrical fault—so I purchased an OBD2AllInOne device (http://www.obd2allinone.com) and tested several programs. Scantool.net (v1.13) provided the most accurate readings—even though it still shows a minor ignition timing anomaly of -64 degrees, which persists even after fixing the issue. I dismissed Digimoto Lite due to its inaccurate values. Using Scantool and OBD2AllInOne allowed me to reset the code and identify a clear pattern: failure at startup, with every second attempt triggering the MIL light—this ruled out loose wiring or intermittent connections. Your suggestion about the cam sensor and distributor led me directly to the root cause. Thanks again—I’ve now fully documented how I resolved this issue.