Error Code P1391 is defined as CMP or CKP Signal Intermittent Condition. It refers to intermittent conditions in the CMP (camshaft position sensor) or the CKP (crankshaft position sensor), which usually happens

This error code is a manufacturer-specific trouble code, meaning it does not apply to all vehicles. Rather, it applies only to specific vehicle makes, such as Dodge and Jeep. Specification on the definition, troubleshooting, and repairs still vary from one make and model to another.

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Error Code P1391 happens when the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected that the actual position of the CMP disagrees with its expected level as set by the manufacturer.

Common Symptoms

Aside from the activation of the Check Engine light and registration of the code in the vehicle’s system, this error code can also show drivability issues as its symptoms. These include:

Engine power lossHard starting or no start at allEngine stumbles or stalls

Possible Causes

In many cases, Error Code P1391 happens when the timing chain has jumped due to a recent change of the sensors. Other possible causes include:

Faulty CKPOpen or shorted CKP sensor harnessPoor electrical connection in the CKP sensorStretched or jumped timing belt or chainFaulty CMPOpen or shorted CMP sensor harnessPoor electrical connection in the CMP sensor

This could also happen if the coils and injectors are getting fired intermittently. Something you would expect if the PCM is getting a weak signal.

How to Check

Have you recently changed sensors? If yes, then the timing could be off, which is causing this problem.

If you have replaced the sensors and have checked the wiring, the next thing you need to check is the timing, and that will include removing the covers.

How to Fix

If you have changed the sensors recently, then you should test the timing chain and make sure the timing mark lines up. This is usually the most common scenario, and relatively easy to fix.

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Other repairs include:

Repair or replacement of CKP sensor harnessRepair or replacement electrical connection in CKP sensorRepair or replacement of CMP sensor harnessRepair or replacement electrical connection in CMP sensor

In many cases, this problem arises from unreliable aftermarket sales parts. Thus, it is always wise to install dealer sensors first, as they’re more reliable and fits perfectly with your vehicle.