Diagnostic Code P068B – PCM Power Relay Malfunction
What is Code P068B?
Code P068B is a generic diagnostic trouble code (DTC) that applies to OBD-II vehicles produced from 1996 onward. This code primarily concerns brands such as Audi, Chrysler, Dodge, Jeep, Ram, Volkswagen, etc. Although generic, repair steps may vary depending on the model and powertrain configuration.
This code indicates that the engine control module (ECM/PCM) has detected a problem in the shutdown procedure of the power relay that supplies it with voltage. In other words, the PCM power relay does not deactivate as quickly as it should.
The PCM power relay is a critical component that safely applies battery voltage to the PCM circuits. It must deactivate in a controlled manner to prevent voltage spikes and potential damage to the control module.
Severity of Code P068B
Code P068B is considered serious. It can lead to engine starting issues and various malfunctions affecting vehicle performance. Therefore, it is recommended to address it promptly.
Symptoms of Code P068B
Common symptoms associated with this code include:
- Delayed or failed starting
- Weak or drained battery issues
Possible Causes of Code P068B
Several causes may be at the root of this code:
- Faulty PCM power relay
- Blown fuse or damaged fuse connection
- Open or short circuit between the power relay and the PCM
Diagnostic and Repair Steps
1. Required Tools
To diagnose a P068B code, you will need:
- An OBD-II diagnostic scanner
- A digital voltmeter/ohmmeter (DVOM)
- A source of technical information for the vehicle
2. Reading and Recording Codes
- Connect the scanner to the vehicle’s OBD-II port
- Retrieve the fault codes and freeze frame data
- Clear the codes and test the vehicle to see if the code reappears
If the code does not return immediately, it may be intermittent, which complicates diagnosis.
3. Visual Inspection
- Check the wiring and connectors associated with the PCM power relay
- Look for damaged, disconnected, or corroded wires
- Repair or replace faulty components
4. Checking Fuses and Relays
- Test all fuses and relays related to the PCM power system
- If a fuse is blown, identify and correct the cause before replacing it
5. Testing the PCM Power Relay
- Check if battery voltage is present at the relay connector
- Ensure the relay properly switches voltage to the PCM
- Replace the relay if necessary
6. Checking the Relay Output Circuit
- If the PCM power relay voltage is correct, test the relay output circuit to the PCM
- If no output signal is detected, there may be an open circuit or a short circuit
7. Testing the PCM
- If all previous steps are correct, the PCM itself may be at fault
- Check for any technical service bulletins (TSBs) regarding PCM software updates
- Replace or reprogram the PCM if necessary
Conclusion
Code P068B can cause serious problems affecting engine starting and reliability. Accurate diagnosis and prompt repair are essential to prevent more significant failures. By following the steps above, you can effectively identify and resolve this issue.