Troubleshoot

ECM/PCM Power Relay Troubles: Understanding the P0685 Code

Ecm Pcm Power Relay Troubles Exploring The P0685 Code
Ecm Pcm Power Relay Troubles Exploring The P0685 Code

If you’re experiencing issues with your vehicle’s ECM/PCM power relay, you might see the P0685 code show up on your diagnostic code reader. This code indicates that there is a problem with the power relay, which is responsible for providing power to the engine control module and the fuel injection system. If left unresolved, this issue can lead to serious problems with your vehicle’s performance and fuel efficiency.

A hand reaches for the hood latch of a car, with the engine compartment open and wires and relays visible.

The focus is on the ECM/PCM power relay, with the P0685 trouble code displayed on a diagnostic tool

One of the most common symptoms of a faulty ECM/PCM power relay is difficulty starting your vehicle. You might also notice that your engine is running rough or that your fuel economy has decreased. In some cases, your vehicle might even stall while you’re driving. If you’re experiencing any of these symptoms, it’s important to get your vehicle checked out as soon as possible to prevent further damage.

Understanding the P0685 Code

If you’re experiencing issues with your car’s ECM/PCM power relay, you may have seen the P0685 code pop up on your OBD-II scanner. This code indicates that there is a problem with the power relay control circuit, which can lead to a variety of issues with your vehicle’s performance.

The P0685 code is often accompanied by symptoms such as difficulty starting the engine, stalling, and rough idling. These issues can be frustrating and potentially dangerous, so it’s important to address them as soon as possible.

To properly diagnose and fix the problem, you’ll need to understand the underlying causes of the P0685 code. In many cases, this code is triggered by a faulty relay or a damaged wiring harness. Other potential causes include a blown fuse, a malfunctioning PCM, or a problem with the battery or alternator.

If you’re not comfortable diagnosing and repairing these issues yourself, it’s best to take your car to a qualified mechanic. They can use specialized tools and techniques to identify the root cause of the problem and make the necessary repairs.

In some cases, the P0685 code may be caused by a more serious issue, such as a damaged ECM or PCM. If this is the case, you may need to replace these components to fully resolve the problem.

Overall, the P0685 code is a clear indication that there is a problem with your car’s ECM/PCM power relay. By understanding the underlying causes of this code and taking appropriate action, you can keep your vehicle running smoothly and avoid potentially costly repairs down the road.

ECM/PCM Power Relay Function

The ECM/PCM power relay clicks as it sends power to the control module, activating the vehicle's systems.

The relay is highlighted with diagnostic code P0685

The ECM/PCM power relay is a critical component of your vehicle’s electrical system. Its primary function is to provide power to the engine control module (ECM) or powertrain control module (PCM) so that it can operate properly.

The ECM/PCM power relay is typically located in the engine compartment and is controlled by the ignition switch. When you turn the key to the “on” position, the ignition switch sends a signal to the relay, which then sends power to the ECM/PCM.

Without the ECM/PCM power relay, your vehicle’s engine control module would not receive the power it needs to function. This can cause a variety of problems, including poor fuel economy, reduced performance, and even engine stalling.

It’s important to note that the ECM/PCM power relay is not the same as the fuel pump relay, although they may be located near each other in the engine compartment. The fuel pump relay is responsible for providing power to the fuel pump, which is necessary for fuel delivery to the engine.

If you’re experiencing problems with your vehicle and have received a P0685 code, it’s possible that the ECM/PCM power relay is failing or has already failed. It’s important to have this issue diagnosed and repaired as soon as possible to prevent further damage to your vehicle’s electrical system.

What is the relationship between the P0650 code and ECM/PCM power relay issues?

The P0650 code insights malfunction indicator relates to ECM/PCM power relay issues. This code indicates that there is a malfunction with the power relay, which may result in the ECM/PCM not receiving the necessary power. It is essential to address this issue promptly, as it can cause various electrical and engine performance problems.

Common Symptoms of P0685

A car engine with a visible power relay connected to the ECM/PCM.

The relay is highlighted, emitting sparks or smoke to indicate trouble

If you are experiencing a P0685 code, there are a few common symptoms that you may notice. These symptoms can help you identify the issue and determine if the ECM/PCM power relay is the culprit.

Engine Stalling

One of the most common symptoms of a faulty ECM/PCM power relay is engine stalling. If your engine stalls while driving or idling, it could be a sign that the power relay is failing. This is because the power relay is responsible for supplying power to the ECM/PCM, which controls the engine’s operation. If the power relay fails, the ECM/PCM may lose power, causing the engine to stall.

No Start Condition

Another symptom of a faulty ECM/PCM power relay is a no start condition. If you turn the key and the engine does not start, it could be due to a failed power relay. This is because the power relay is responsible for supplying power to the starter and fuel system. If the power relay fails, the starter and fuel system may not receive the power they need to start the engine.

Check Engine Light

A P0685 code will trigger the check engine light to turn on. The check engine light is a warning indicator that something is wrong with the engine or emissions system. If you see the check engine light turn on, it is important to have the code diagnosed and repaired as soon as possible. Ignoring the check engine light can lead to further damage to the engine or emissions system.

By understanding the common symptoms of a P0685 code, you can identify the issue and take the necessary steps to repair it. If you are experiencing any of these symptoms, it is important to have your vehicle diagnosed by a qualified technician to determine the cause of the issue.

Diagnostic Steps for P0685

A mechanic connects a diagnostic tool to a vehicle's ECM/PCM to troubleshoot P0685 code.

Wires and connectors are visible along with the power relay

If you’re experiencing ECM/PCM power relay troubles and have received the P0685 code, there are a few diagnostic steps you can take to identify the root cause of the issue. Here are some steps to follow:

  1. Check the battery voltage: The first step is to check the battery voltage. Low voltage can cause the P0685 code to appear. Use a digital multimeter to check the battery voltage. If the voltage is low, charge the battery and retest.

  2. Check the fuses: The next step is to check the fuses. A blown fuse can cause the P0685 code to appear. Use the owner’s manual to locate the fuse box and check the fuses related to the ECM/PCM power relay. Replace any blown fuses and retest.

  3. Check the wiring: The third step is to check the wiring. A damaged or corroded wire can cause the P0685 code to appear. Use a wiring diagram to locate the wires related to the ECM/PCM power relay and check them for damage or corrosion. Repair or replace any damaged wires and retest.

  4. Check the ECM/PCM power relay: The final step is to check the ECM/PCM power relay. A faulty relay can cause the P0685 code to appear. Use a digital multimeter to check the resistance of the relay. If the resistance is out of spec, replace the relay and retest.

By following these diagnostic steps, you can identify and fix the root cause of the P0685 code. If you’re not comfortable performing these steps yourself, it’s best to take your vehicle to a qualified mechanic for diagnosis and repair.

Repair and Solution Strategies

A hand reaching for a power relay module in a vehicle's engine compartment, with diagnostic equipment connected to the ECM/PCM, displaying the P0685 trouble code

If you have diagnosed the P0685 code as a faulty ECM/PCM power relay, there are a few strategies you can use to repair and solve the issue.

First, you should check the relay’s wiring and connections to ensure they are secure and in good condition. If any damage is found, repair or replace the affected components.

Next, you can try replacing the ECM/PCM power relay with a new one. Be sure to choose a high-quality replacement that is compatible with your vehicle’s make and model.

If the issue persists after replacing the relay, you may need to inspect the ECM/PCM itself for any faults or damage. In this case, it is recommended to seek the assistance of a professional mechanic or technician to properly diagnose and repair the issue.

It is important to note that attempting to repair or diagnose electrical issues on your own can be dangerous and should only be done if you have the proper knowledge and experience. Always follow proper safety procedures and use caution when working with electrical components.

By following these strategies and taking the necessary precautions, you can effectively repair and solve ECM/PCM power relay troubles and clear the P0685 code from your vehicle’s diagnostic system.

About the author

The Motor Guy

The Motor Guy is a passionate car enthusiast with a love for troubleshooting and diagnosing all sorts of vehicle problems.

With years of experience in OBD diagnostics, he has become an expert in identifying and solving complex automotive issues.

Through TheMotorGuy.com, he shares his knowledge and expertise with others, providing valuable insights and tips on how to keep your vehicle running smoothly.

Qualifications:
- 12 years experience in the automotive industry
- ASE Master Automobile Technician
- A Series: Automobile and Light Truck Certification, A9 Light Vehicle Diesel Engine Certification
- Bachelor's Degree in Information Systems