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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.
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.
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 loss
- Hard starting or no start at all
- Engine stumbles or stalls
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 CKP
- Open or shorted CKP sensor harness
- Poor electrical connection in the CKP sensor
- Stretched or jumped timing belt or chain
- Faulty CMP
- Open or shorted CMP sensor harness
- Poor 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.
Other repairs include:
- Repair or replacement of CKP sensor harness
- Repair or replacement electrical connection in CKP sensor
- Repair or replacement of CMP sensor harness
- Repair 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.