What Is the P0688 Code?
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Seriousness
Can I Still Drive?
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Code P0688 is a very generic powertrain code. The code definition indicates that the relay control circuit, which supplies the Powertrain Control Module (PCM) or Engine Control Module (ECM) with power, sends out an abnormal voltage reading. This can indicate all kinds of issues with the ECM or PCM. The problem can also extend to the Engine Control Unit (ECU), also called an Electronic Control Unit. As a generic engine code, you may find the P0688 trouble code in a wide array of vehicle manufacturers. Still, the code will only appear in vehicles that use a PCM or ECM relay to supply the module with power and ground signals.
More About Error Code P0688
The PCM is the main “computer” of your vehicle, with the ECM functioning as the computer that controls engine performance. These computers perform a wide variety of functions, ranging from ensuring that the air/fuel ratio is at its most effective to tracking the vehicle’s temperature to ensure it doesn’t get too hot. A PCM/ECM relay supplies battery voltage to the PCM or ECM, which needs a ground signal and an “on” position for the ignition switch. If the output signal is outside the manufacturer-defined parameters, the P0688 diagnostic trouble code will be stored.
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What Are the Symptoms of a P0688 Code?
It depends on the specific vehicle and the precise reasons that your vehicle is showing this fault code. In some cases, there may be no symptoms other than the stored code, while in others, you may have to deal with a complete no-start condition. The check engine light or other warning light may illuminate. But in some situations, the check engine light may not illuminate despite your vehicle storing codes that typically cause it to illuminate. The common symptoms of the P0688 code, especially those that cause drivability symptoms, are extremely varied and difficult to predict. You usually only discover it once you use a diagnostic tool to pull error codes.
What Are Some Causes of a P0688 Code?
The P0688 code can occur due to a variety of reasons. A faulty or damaged PCM or ECM relay can result in this code, as can problems with damaged, defective, corroded, and loose electrical wiring and issues with related connectors and connector pins. There may be a problem with the battery, including low battery charge. The ECM or PCM can sometimes be damaged or defective, although this is uncommon and should definitely be the last-case scenario.
How Serious Is the P0688 Code?
Most experts will consider the P0688 code as potentially serious. Even if the drivability isn’t impacted due to the P0688 code initially, it can develop into serious drivability concerns over time, as the PCM and ECM are responsible for many functions within the vehicle. Regardless of whether or not you’re noticing drivability concerns related to the P0688 code right now, you should fix the code as quickly as possible to avoid running into those problems later.
Can I Still Drive with a P0688 Code?
In many cases, you won’t physically be able to drive with the P0688 code, as this code can result in a complete no-start condition, where you can’t even turn the vehicle on. Even if the vehicle starts and seems to drive effectively, you don’t want to risk driving if your car does not have all the necessary inputs to be safe. If the P0688 code is active in your vehicle, it’s a good idea to stop driving until you’ve fixed the problem.
How Easy Is It to Diagnose a P0688 Code?
Diagnosing a P0688 code can be difficult because several different repairs may be able to fix the P0688 code. You may need to replace or fully charge the battery, replace damaged or blown fuses, replace damaged or corroded electrical wires, discover and repair loose or shorted connections, and even check out the ECM/PCM relay or ECM itself. The diagnosis process can be quite difficult, so it’s best to avoid doing it yourself and get help from an experienced mechanic.
How Difficult Is It to Inspect a P0688 Code?
There are many common mistakes that you can make when trying to inspect your P0688 code. For example, you need to go through a flowchart that will help you test for the most common reasons for the P0688 code, and not doing so can lead to you spending hours of time hunting for a problem that may have been right in front of you the whole time. Plus, you need to know the exact repair steps necessary for different fixes, as well as how to understand technical service bulletins that you might need to use as a vehicle information source. Inspection is often difficult for a DIYer, so it’s best to talk to a certified mechanic.
Need Additional Help with Your P0688 Code?
The P0688 code is not always an easy one to fix. However, if you can get help from a professional mechanic, you can easily fix the underlying problem and get your vehicle back on the road.
You’ll want to find an auto repair shop in your area. Especially if your vehicle isn’t starting at all and you need a tow truck, finding a local automobile repair shop should be one of the most important parts of this process.
The KBB.com OBD-II database is also important in understanding the information an OBD-II scanner provides. If you see other error codes pop up on your scan tool, this database will give you insight into those codes and how to fix them.
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