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    P0690 ECM/PCM Power Relay Sense Circuit High

    What does this OBD II code mean? 

    This generic OBD2 code is set when the Powertrain Control Module (PCM) senses a power relay voltage higher than expected.

    Why does this OBD II code appear?

    The Power Relay is used to supply voltage to the PCM, in other words, it’s function is to deliver to the powertrain control module the adequate battery voltage needed for its operation.
    This contact type relay uses the traditional 5-wire design. The control circuit is activated by the ignition switch (pin 86) and the ground (pin 85). The permanent battery voltage is supplied by pin 30 as usual, and the high output voltage is delivered to the PCM by pin 87. The pin 87a is used by the PCM to monitor the relay voltage at all times.
    The OBD2 code P0690 is stored in memory when the PCM detects a supply voltage higher than the acceptable limit.

    What symptoms may occur with this OBD II code?

    Expect the typical symptoms from a P0690 condition:

    • CEL lit. The Check Engine Light will turn on after few driving cycles to alert the driver about the situation. 
    • Hard start or even a no start condition.
    • Some electrical components may not work. 

    What are the causes that trigger this OBD II code?

    There're many factors that could cause a P0690 condition including among others the following:

    • Damaged, burnt, corroded, open or shorted power relay wiring. 
    • Worn, corroded, burnt, disconnected or bent power relay wiring harness connector pins. 
    • Blown fuse (ignition circuit).
    • Faulty or defective power relay.
    • Even when unlikely, a defective PCM cannot be discarded.

    Diagnostic strategy for troubleshooting this OBD II code

    It's highly recommended starting the diagnostic process with the usual information gathering:

    • With the help of a professional OBD2 scan tool, preferably one with OEM capabilities, take note of all data trouble codes in memory, including pending codes.
    • Take note of freeze frame information (if present).
    • Query the vehicle owner about what, when and where the failure occurs. Does it happen with the engine hot? Cold? Under load? All the standard questions.
    • Take note of the vehicle VIN and find a reliable source of technical reference.

    Once you are done, the next step is discarding an intermittent condition. 

    • Using your scan tool clear DTC memory. 
    • Perform a complete driving cycle according to OEM procedures.

    If the code P0690 disappears then inform the owner about the intermittent nature of the code and explain that further testing with the code present will be required. If the code does appear then continue to the testing stage, consisting in discarding the possible causes of the problem. 

    IMPORTANT: the diagnostic procedure explained in this section should be taken as a guideline. Always refer to specific OEM procedures when possible.

    The workflow for the diagnostic process is:

    • The tests should be executed in sequential order, in other words, complete step 1 before going to step 2 and so on.
    • Repair, fix, or replace any component if you suspect is not in good condition.
    • If any repair, fix, reprogramming or component replacement is made during any step then you should clear DTC memory and repeat the whole KOER driving cycle.
    • If the DTC appear again then you should continue to the next step.
    • If the DTC does not appear again after completing the KOER tests then you can assume the problem is fixed, in that case, continuing with the remaining steps would be optional.

    The diagnostic process for the code P0690 is as follows:

    1. Relay harness wiring and connector: carry out an exhaustive visual inspection the PCM power relay wiring and connectors. Pay special attention to burnt, corroded, open, shorted to ground or deteriorated wiring and/or connector. Unplug the relay and check for corrosion, damage, bent pins, etc.
    2. Electrical tests: with the help of a digital volt-ohm meter (DVOM) and the adequate wiring diagram perform a KOEO check on the power relay. Verify the battery supply voltage and/or ignition voltage, electrical resistance, continuity, current and ground integrity. To achieve it, place one DVOM probe in a known ground (battery negative for instance) and the other in the pin 30. You should read battery voltage. Now turn the ignition switch on, engine off (KOEO). Maintain one probe in the negative terminal and use the other to measure pin 86 voltage. You should read battery voltage again if you don’t, check the corresponding fuse. Now place one probe in the terminal 30 and the other in the terminal 85. You should read the same battery voltage as before if you don’t (or is lower than 12V) then you need to check the ground line. 
    3. Relay functional test: install the relay and place one DVOM probe in a known ground. With the other probe, you will measure the output from pin 87a. This pin is constantly energized, so you expect to read battery voltage unless an internal relay problem is present. Finally, turn on the switch ignition with engine off (KOEO). Read the output from pin 87, it should be 12V+. If you completed the electrical test mentioned above and the relay is not supplying the output voltage then you must replace it immediately.
    4. Problems with the powertrain control module: the most unlikely cause for this code is a faulty PCM or a corrupted program. Yet, if you are completely certain that all prior tests passed then you must remove the PCM and check it, reprogram it or replace it as necessary.
       

     

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