You might experience the Diagnostic Trouble Code (DTC) P1391 with your Jeep. The PCM of your Jeep stores this code when it notices differences between actual and expected values with either CKP or CMP.
The code is moderately severe to severe; thus, you must act soon. Throughout this article, we’ll discuss why the code is present and how you can get rid of it.
What Does P1391 Jeep Code Mean?
In simple language, the error number P1391 indicates a problem with either your Crankshaft Position Sensor (CKP), Camshaft Position Sensor (CMP), or both. In mechanical language, it means CKP signal intermittent condition.
Just like in the majority of cars, the Jeep’s Powertrain Control Module (PCM) continuously keeps an eye on each of these CMP and CKP sensors.
The code is stored when the PCM, a unified controller made up of the Transmission Control Unit (TCU) and Engine Control Unit (ECU), notices when the PCM detects the actual CKP position differs from the expected sensor level.
Usually, in a Jeep, the CKP and CMP sensors are utilized to track the position and speed of rotation of the crankshaft and camshaft separately. Then, these sensors transmit signals to the PCM to ensure correct engine functioning and performance.
Using this data, the PCM regulates the timing of the ignition, fuel injection, and other engine processes to guarantee appropriate engine efficiency.
And when the CMP, CKP, or both sensor circuits fail, the PCM displays the P1391 error code and illuminates the engine check light. If we break down the code, we get the following:
- P = stands for powertrain
- 1 = Manufacturer-specific code According to SAE standard
- 3 = It indicates Camshaft Position Sensor (CMP) Or Crankshaft Position Sensor (CKP) Problems
- 91 = specific fault index. In our case, It indicates Camshaft Position Sensor (CMP) Or Crankshaft Position Sensor (CKP) signal intermittent condition.
What Causes the P1391 Code on a Jeep?
Basically, the issues with either CMP or CKP sensor or both cause the P1391 code on a jeep. These two sensors play a crucial role in a Jeep’s driving mechanism.
And these sensors might malfunction for several reasons. Here are the possible reasons behind these sensor malfunctions.
1. Reasons Behind Camshaft Position Sensor Issues
Image Source: Replacing BANK 1 Camshaft Position Sensor Jeep JK
The majority of camshaft position sensors used in Jeep come from a range of different manufacturers, including MOPAR, Bosch, Delphi, and more. Though MOPAR is an Original Equipment Manufacturer of Jeep, others are all third-party parts manufacturers.
Here are the Reasons Behind this Sensor Malfunction:
Mechanical damage to the sensor’s physical structure or internal components might result in inaccurate or inconsistent results. This may cause the Check Engine Light to come on, improper camshaft setting, engine failures, stalling, and poor engine performance.
Internal circuitry connects the sensor to electrical power and the Jeep’s PCU. Faulty wiring connection because of loose wiring, grease, and debris might result in a voltage interruption. Which later affects the CMP sensor’s performance. Approximately 348 wiring-related issues have been reported on Carproblemzoo.
Damaged Encoder Wheel:
The CMP sensor’s encoder wheel spins in time with the camshaft and transmits data about the camshaft’s position to the sensor. CMP will produce wrong or irregular signals if this encoder wheel is damaged.
Internal Short Circuits:
Internal short circuits cause electricity to travel down the incorrect channel rather than the CMP sensor. The most common causes of short circuits include unsecured connections, faulty insulation, and corroded wires. According to Carproblemzoo, since 1996, 12,799 issues involving the electrical system have been reported by Jeep owners.
Leaking Engine Oil:
The CMP sensor’s ability to transmit signals may be hindered or reduced if engine oil escapes and somehow gets inside. Engine oil may leak due to inadequate tightening or the absence of engine components, which might destroy the sensor.
Melting or Overheating:
A CMP sensor has several little and sensitive components, and excessive heat might physically harm its internal parts. So, because of overheating, the sensor may operate inconsistently or unpredictably.
2. Reasons Behind Crankshaft Position Sensor Issues
Image Source: How to Test Crankshaft and Camshaft Position Sensors
The Crankshaft Position (CKP) Sensor keeps track of the crankshaft’s location and rate of rotation. It transmits crankshaft position data to the PCM to control ignition timing and fuel injection.
The same manufacturer that makes camshafts also makes crankshafts, and as these sensors age, they lose their efficiency and functionality. Here are several leading causes of the sensor’s malfunction.
The CKP sensor may stop working as a result of an overheated engine. Although each CKP sensor is designed to withstand engine heat, excessive engine heat might impair it’s performance.
Any metal shavings produced by friction in the engine can stick to the sensor’s magnet or the wheel, which causes the sensor readings to be hampered and shows the P1391 code.
Defective or Short Circuits:
There is a chance that a faulty or shorted circuit will cause the CKP sensor to malfunction. Flawed circuits will hamper the main purpose of the sensor because they will never correctly transmit the signals to PCM.
Issues with Reluctor Ring Teeth:
The PCM won’t be able to analyze a low or unstable signal produced by bent, damaged, or cracked reluctor ring teeth, which will result in the P1391 Code being displayed.
Faulty Timing Belt:
A broken timing belt might cause significant damage to the crank sensor. If a timing belt is damaged in a collision or snaps due to regular wear, the belt may tie around the crankshaft sensor, destroying sensors and equipment.
Damaged Wheels and Pins:
The crankshaft’s position is measured by the sensor wheel, which is connected to the crankshaft. Additionally, the information is sent to the PCM through the sensor pins.
Your Jeep will display the P1391 Code if the pins or wheel are damaged because the signal pattern will be disturbed.
How to Troubleshoot & Fix P1391 Jeep Code?
As you are already aware, your Jeep’s P1391 code is primarily caused by CMP and CKP sensor issues. But, there are several aspects associated with these two reasons.
So, to help you identify the precise cause, we will walk you through every reasonable troubleshooting step in this section. You’ll also have a good idea of what steps you might take to fix them.
1. Check the CKP Sensor:
The CKP sensor is in charge of delivering crankshaft position indications to the PCM. Without a properly working CKP sensor, the PCM will be unable to precisely manage the ignition timing, resulting in the P1391 code.
To diagnose a defective CKP sensor, use a multimeter to measure its resistance. Replacing the sensor is necessary if you don’t get any values or get a high reading from the allowed range (between 200 and 2000 ohms).
This problem is typically resolved by changing the sensor, which might cost between $150 and $250.
2. Check the CMP Sensor:
If you already find that the CKP sensor is okay, there’s a high chance that your CMP sensor is faulty.
The CMP sensor’s primary duty is to provide information about the position of the crankshaft to the PCM. Similar to the CKP, if this sensor malfunctions, the PCM won’t be able to take the essential actions to keep the engine operating smoothly.
Check the CMP sensor resistance value to determine its present condition, precisely as you did with the CKP sensor. Here a good CMP sensor resistance value will be between 200 to 1,000 ohms.
If you get this value, it means the CMP sensor is okay; otherwise, it’ll become faulty, and you will have to install a new one. You might have to pay between $200 and $400 to replace it.
Here is a short video that might help you know how to check and replace the CMP sensor.
3. Check the Connections and Wiring:
If you’ve completed the troubleshooting mentioned above and your Jeep still displays the P1391 code, there might be a wiring or connection issue.
In this case, you must thoroughly inspect the connections between the CKP, CMP sensors, and PCM. If you discover any damage or loose connections, fix or replace the wiring as needed. You can accomplish it on your own without paying any money.
4. Check for any Blown Fuses:
If your Jeep is still showing the P1391 code, there could be an issue with the fuses.
The CKP, CMP, and PCM require electricity to function, and fuses prevent overvoltages from reaching these components. When a fuse receives an overvoltage, it blows and cuts off any electrical circuit.
In this case, you must inspect the fuses associated with these electrical components.
To locate the proper fuses, see your Jeep’s owner’s manual. If you find any blown ones, simply replace them with identical new ones. This might cost you between $10 and $20.
5. Check Powertrain Control Module (PCM):
There is a good likelihood that the PCM is malfunctioning if you continue to receive the P1391 error code.
A PCM collects data from CKP and CMP sensors. When this PCM module malfunctions, it cannot analyze this data and take the necessary steps to run an engine.
Additionally, it will cause the engine to backfire, struggle to start, and rapidly degrade essential engine parts.
Symptoms of a faulty PCM in a Jeep:
- Your car stops or sputters.
- The engine check light is on.
- Unexpectedly, mileage has decreased.
- Having trouble starting your Jeep.
- Your Jeep appears to be shifting abruptly or randomly.
Along with these symptoms, you must check the wiring and battery to identify an issue. Here, if you find it faulty, you have to replace it. This might cost you between $650 and $750.
Even after reading this essay, you could still have some queries. Check out these frequently asked questions to learn more. We did our best to respond properly to these inquiries.
Can You Drive A Jeep With P1391 Code?
As we already explained, this code denotes a problem with the CMP and CKP sensors, which are connected to the engine of your Jeep. Therefore, operating a jeep in this situation might be risky and could harm the vehicle.
How Much Does It Cost To Fix Jeep P1391 Code?
Basically, the cost of fixing the Jeep P1391 code depends on the issues, Jeep model, and parts availability. However, minor issues may cost between $50 and $300, while significant difficulties may cost between $300 and $800.
How Can You Avoid Getting P1391 Codes On Jeep?
You can easily avoid getting the P1391 code on your Jeep by doing regular maintenance, practicing proper driving skills, monitoring engine performance, avoiding overloading, and keeping the Jeep away from moisture. In addition, you must constantly take action for small difficulties.
Finally, wherever possible, use genuine OEM Jeep components. To be fair, most of the aftermarket parts are either poorly constructed or composed of cheap materials.
As a result, they never last long. Additionally, never order ‘suspected’ malfunctioning parts without first performing the above-mentioned troubleshooting.