P0688 Code: ECM / PCM Power Relay Sense Circuit Open

Is your vehicle having problems? Use a scan tool to check if your vehicle has any stored trouble codes so you can find the exact problem. If you see the P0688 code, read on to learn more about its definition, common causes, and common symptoms.

What Does the P0688 Code Mean?

Diagnostic trouble code (DTC) P0688 stands for ECM/PCM Power Relay Sense Circuit Open. A stored P0688 code can indicate that the powertrain control module (PCM) has detected an issue in the relay that gives it power from the battery (or the fuel injectors and ignition coils power from the battery). In this case, it could mean there’s a problem with the relay or its circuit.

Note: The definition of the P0688 code can be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P0688 Code

The P0688 code can be caused by:

• A defective PCM power relay
• Faulty PCM
• Blown fuse or fusible link
• A circuit problem, such as a damaged wire or poor connection

What are the Common Symptoms of the P0688 Code

When triggered, the P0688 can show the following symptoms:

• Illuminated check engine light
• The vehicle refuses to start
• The vehicle stalls

How to Diagnose the P0688 Code

While the definition of the P0688 code implies that the issue is PCM-related, this is not always the case. To resolve this DTC, you must first identify the root cause. This might need a visual inspection of the concerned components. This job could also require the use of specific tools that are not readily available to you. If you’re new to DIY repairs, we recommend consulting with a professional mechanic.

Do you want to learn how to diagnose the issue on your own? The video below will give you an idea of what the process might involve.

How to Fix the P0688 Code

When it comes to addressing OBD-II codes, there isn’t a single solution that will surely fix the issue. You must first diagnose the problem accurately in order to determine the best course of action.

Once you’ve figured out the cause of the P0688 issue, then you can seek solutions from credible internet repair resources and how-to guides.

You can refer to Chilton repair manuals, or you can try an ALLDATA subscription, which provides detailed factory repair information.

If you don’t have much expertise in diagnosing or correcting error codes, it’s advisable to consult a professional mechanic.