P068B ECM/PCM power relay de-energized - too late

OBD-II DTC Datasheet

ECM/PCM power relay de-energized - too late

What does this mean?

This is a generic Diagnostic Trouble Code (DTC) applicable to many OBD-II vehicles (1996 and newer). This may include, but is not limited to, Audi, Chrysler, Dodge, Jeep, Ram, Volkswagen, etc. Despite the general nature, the exact repair steps may vary depending on the model year, make, model and transmission configuration.

If a P068B code is stored, the engine / powertrain control module (ECM / PCM) has detected a malfunction in disconnecting power to the relay that energizes it. In this case, the PCM power relay does not de-energize quickly enough.

The PCM power relay is used to safely supply battery voltage to the appropriate PCM circuits. This is a contact type relay that is activated by a signal wire from the ignition switch. This relay must be de-energized gradually to avoid power surges and possible damage to the controller. This type of relay usually has a five-wire circuit. One wire is supplied with constant battery voltage; land on the other. The third circuit supplies the signal from the ignition switch, and the fourth circuit supplies voltage to the PCM. The fifth wire is the power relay sensor circuit. It is used by the PCM to monitor the supply relay voltage.

If the PCM detects a malfunction when the ECM / PCM relay is powered off, a P068B code will be stored and a malfunction indicator lamp (MIL) may illuminate.

Typical PCM Powertrain Control Module disclosed:

What is the severity of this DTC?

The P068B code must be classified as serious and dealt with accordingly. This can lead to inability to start and / or to various problems with the vehicle's handling.

What are some of the symptoms of the code?

Symptoms of a P068B trouble code may include:

Delayed start or not
Weak or discharged battery problems

What are some of the common causes for the code?

Reasons for this code may include:

Faulty PCM Power Relay
Blown fuse or fuse
Open or short circuit in the circuit between the power relay and the PCM

What are some steps to troubleshoot the P068B?

A diagnostic scanner and a digital volt / ohmmeter (DVOM) are required to diagnose the P068B code.

You will also need a source of reliable information about the vehicles. It provides diagnostic block diagrams, wiring diagrams, connector faces, connector pinouts, and component locations. You will also find procedures and specifications for testing components and circuits. All this information will be required to successfully diagnose the P068B code.

Connect the scanner to the vehicle diagnostic port and get all stored codes and freeze frame data. Make a note of this information as it may be helpful if the code turns out to be intermittent.

After recording all relevant information, clear the codes and test drive the vehicle (if possible) until the code is cleared or the PCM enters ready mode.

If the PCM enters ready mode, the code will be intermittent and even more difficult to diagnose. The condition that led to the persistence of P068B may need to worsen before an accurate diagnosis can be made. On the other hand, if the code cannot be cleared and the symptoms of handling do not appear, the vehicle can be driven normally.

Consult your vehicle information source for technical service bulletins (TSBs) that reproduce the stored code, vehicle (year, make, model and engine) and symptoms detected. If you find an appropriate TSB, it can provide useful diagnostic information.

If the P068B code resets immediately, visually inspect the wiring and connectors associated with the system. Belts that have been broken or unplugged should be repaired or replaced as needed.

If the wiring and connectors are OK, use your vehicle information source to obtain related wiring diagrams, connector face views, connector pinout diagrams, and diagnostic block diagrams.

Once you have the information you need, check all fuses and relays in the system to ensure that battery voltage is being supplied to the PCM power supply relay.

Obtain the PCM relay power off parameters and apply them to the next diagnostic steps.

If there is no DC (or switched) voltage at the power relay connector, trace the appropriate circuit to the fuse or relay from which it comes. Repair or replace defective fuses or fuses as necessary.

If the relay power supply input voltage and ground are present (at all appropriate terminals), use the DVOM to test the performance of the relay output at the appropriate connector pins. If the voltage of the output circuit of the power supply relay does not meet the requirements, suspect that the relay is faulty.

If the PCM power supply relay output voltage is within specification (at all terminals), check the appropriate relay output circuits on the PCM.

If a relay output voltage signal is detected at the PCM connector, suspect a faulty PCM or a PCM programming error.

If no matching PCM power relay voltage output signal is found on the PCM connector, suspect an open or short circuit between the PCM power relay and the PCM.

Fuses and fuses should be checked with a loaded circuit to avoid misdiagnosis.

Related DTC discussions

Jeep grand cherokee P2006B 068 model yearHi, my 2006 Grand Cherokee 3000 CRD engine lights up, I run diagnostics and give me the code P068B, I was This shows that the car is working fine and no signs of abnormalities many thanks to Simone ...

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