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P0688 is a diagnostic trouble code (DTC) for "ECM/PCM Power Relay Sense Circuit/Open". 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.
The P0688 code is a generic powertrain code related to output circuit issues, including internal computer failures. In this case, the engine control module (ECM), also known as a powertrain control module (PCM) has signaled too much power to the power relay sense circuit, which powers the: ECM/PCM.
A code P0688 will be stored when the relay control circuit that supplies the ECM with power sends out a high or abnormal voltage reading.
Vehicles that use a PCM/EC relay to supply the ECM with power and ground signals will be the only type of vehicles in which this code will be stored.
A PCM/ECM relay supply battery voltage, and/or ground signals are sent to the ECM, which need a battery voltage and ground signal, as well as the ignition switch to be in the “on” position to operate. The output signal also supplies the ECM with vehicle data. When the ECM is sent a signal that is outside of present manufacturer parameters, a code P0688 code can be stored.
Several problems may cause a P0688 code including:
Symptoms of a P0688 code may include:
A mechanic may use several methods to diagnose a P0688 trouble code, including:
As replacing a vehicle’s ECM/PCM requires reprogramming, it is recommended to be sure to test and repair all other possible symptoms and problems that could cause a stored P0688 code.
Because a vehicle’s safe driving operation most likely will be impacted due to faults that store a P0688 code, this code is considered a potentially serious code. When this code appears, it is recommended to immediately take your vehicle to your local service center or mechanic for repair and diagnosis.
Several repairs can fix a P0688 trouble code and include:
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