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P0687 is a diagnostic trouble code (DTC) for "ECM/PCM Power Relay Control Circuit High". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
A P0687 code is stored when the PCM (powertrain control module) detects an incorrect, abnormal, or erratic voltage reading from the relay control circuit that supplies it with its power.
In most cases, when the PCM stores a P0687 code, it’s because it has detected overly high voltage from its power supply. When everything is working normally, the PCM receives a steady flow of power from the battery through a contact relay. If the voltage coming from the battery through this relay is too high, the PCM will store the P0687 code and illuminate the Check Engine light.
Some of the most common causes for a P0687 code are:
In most cases, the illuminated Check Engine light will be the only symptom for the P0687 code. In some instances, though, a no-start condition will occur, preventing the vehicle from starting in order to protect the PCM from damage.
After identifying the P0687 code with an OBD-II scanner, the mechanic will begin by inspecting the wiring and connectors between the battery and the PCM. If there is evidence of damage, corrosion, a short, or an open circuit, they will repair the issue and then clear the code and attempt to start the vehicle again to check if the code is set once more.
If the code still sets after this, they will inspect and test the alternator’s performance, the ignition switch, and all other components and wiring related to the PCM power relay. After each test and repair, they will clear the codes and retest the system.
If you’re in too much of a rush to diagnose the problem, you may believe that the PCM needs to be replaced to allow the vehicle to start again. Doing this without fixing the actual underlying cause of the P0687 code will be expensive and unnecessary. With a thorough inspection and diagnosis, you may be able to save a lot of time, energy, and money.
If the P0687 code results in a no-start condition, then the problem will need to be resolved before the vehicle is drivable. Even if there isn’t a no-start condition and the vehicle can be started and driven, though, it’s important to note that too much voltage sent to the PCM can severely damage it. The longer you go without resolving the problem, the more likely you are to need an entirely new PCM to fix it.
In many cases, the problem can be resolved by performing one of the following repairs:
If the PCM receives too much voltage or its power supply is erratic, a number of other codes and symptoms can begin to appear. It’s important to note the order in which these codes were stored by the PCM, as this can tell you whether or not they’re related. Don’t just try to resolve the symptoms before thoroughly inspecting the problem, and remember that the PCM may not actually need to be replaced, even if it is malfunctioning and throwing several codes. Replacing a faulty PCM power relay could be the solution to the problem, and it could save you a great deal of money and frustration.
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.