Diagnostic guide for P1391

Diagnostic Guide for P1391 - CMP or CKP Signal Intermittent Condition

The P1391 code indicates an intermittent issue with the Camshaft Position Sensor (CMP) or Crankshaft Position Sensor (CKP) signals. The goal of this diagnostic guide is to identify the root cause of the discrepancy between the actual and expected sensor readings, ensuring proper engine performance.

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Difficulty

Intermediate

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Estimated Time

30-60 Minutes

Estimated Diagnostic Cost

$0-$100

Typical shop charge to perform this diagnostic process. Repair parts and labor are not included.

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Tools Needed

OBDII scanner, multimeter, wiring diagram, basic hand tools

Safety Notes

Ensure the engine is off and cool before starting. Use caution when working around moving parts and electrical systems. Disconnect the battery when inspecting wiring.

Step 1

Check OBDII Codes

Instruction Connect an OBDII scanner to the vehicle's diagnostic port and retrieve any stored trouble codes.

Expected result The scanner should display the P1391 code along with any other related codes.

If Pass If P1391 is confirmed, proceed to the next step to inspect the sensors.

If Fail If P1391 is not present, further diagnostics may be needed for other codes or issues.

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Step 2

Inspect CKP and CMP Sensors

Instruction Visually inspect the Crankshaft Position Sensor and Camshaft Position Sensor for any signs of damage, corrosion, or loose connections.

Expected result Sensors should be intact, with clean and secure connections.

If Pass If the sensors appear in good condition, proceed to test the electrical connections.

If Fail If damage or poor connections are found, repair or replace the affected sensors or connectors.

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Step 3

Test Electrical Connections

Instruction Using a multimeter, test the voltage and ground at the CKP and CMP sensor connectors while the engine is cranked.

Expected result You should measure the specified voltage and ground as per the vehicle's wiring diagram.

If Pass If voltage and ground are present, the sensors are likely functioning correctly. Proceed to check the timing belt or chain.

If Fail If there is no voltage or ground, inspect the wiring harness for shorts or opens, and repair as necessary.

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Step 4

Check Timing Belt or Chain

Instruction Inspect the timing belt or chain for signs of wear, stretching, or misalignment.

Expected result The timing belt or chain should be tight and properly aligned with no visible damage.

If Pass If the timing components are in good condition, further diagnostics may be needed on the PCM.

If Fail If the timing belt or chain is stretched or misaligned, it may need to be replaced or adjusted.

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Step 5

Clear Codes and Test Drive

Instruction Clear the trouble codes using the OBDII scanner and take the vehicle for a test drive to see if the code reappears.

Expected result The check engine light should remain off during the test drive if the issue is resolved.

If Pass If the code does not return, the issue is likely resolved. Monitor the vehicle for any future symptoms.

If Fail If the code reappears, further investigation into the PCM or sensor replacement may be necessary.

Ask Coddy about this step

Coddy can help with this step only. Tell me what you tested or what result you got.