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P0685 2015 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Open

Quick Answer

The P0685 diagnostic trouble code (DTC) for a 2015 GMC Sierra indicates that there is an issue with the Engine Control Module (ECM) Power Relay Control Circuit being open. Common causes include Faulty ECM power relay, Loose or corroded electrical connections, Wiring harness issues. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P0685 2015 GMC Sierra indicates Engine Control Module Power Relay Control Circuit Open.
Common causes
Common causes include Faulty ECM power relay, Loose or corroded electrical connections, Wiring harness issues.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 16, 2024
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Code P0685 2015 GMC Sierra Description

The P0685 diagnostic trouble code (DTC) for a 2015 GMC Sierra indicates that there is an issue with the Engine Control Module (ECM) Power Relay Control Circuit being open. The ECM, also known as the engine control unit (ECU), is a crucial component of the vehicle's electronic control system. It is responsible for managing various engine functions, such as fuel injection, ignition timing, and emissions control. The power relay control circuit is a part of the ECM that controls the power supply to the ECM itself.

OBDII Code P0685 2015 GMC Sierra - Engine Control Module Power Relay Control Circuit Open
P0685 2015 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Open

Common Causes of P0685 2015 GMC Sierra

  1. Faulty ECM power relay
  2. Loose or corroded electrical connections
  3. Wiring harness issues
  4. ECM software malfunction
  5. ECM hardware failure

Symptoms of P0685 2015 GMC Sierra

  1. Check engine light illuminated on the dashboard
  2. Engine misfires or rough idling
  3. Reduced fuel efficiency
  4. Stalling or difficulty starting the engine
  5. Loss of power or acceleration

How to Fix P0685 2015 GMC Sierra

  1. Begin by conducting a thorough inspection of the ECM power relay and its associated wiring harness. Check for any visible signs of damage, corrosion, or loose connections.
  2. Test the ECM power relay using a multimeter to determine if it is functioning correctly. Replace the relay if it is found to be faulty.
  3. Inspect the wiring harness for any breaks, shorts, or damage. Repair or replace any damaged wiring as needed.
  4. Clear the DTC from the vehicle's ECM using a diagnostic scan tool. Test drive the vehicle to ensure that the issue has been resolved and that the check engine light does not reappear.
  5. If the problem persists, consult a professional mechanic or dealership for further diagnosis and repair.

Cost to Fix P0685 2015 GMC Sierra

The typical repair costs for addressing a P0685 code on a 2015 GMC Sierra can vary depending on the specific cause of the issue and the extent of the repairs needed. In general, replacing an ECM power relay or repairing wiring harness issues can range from $100 to $300 in parts and labor. However, it is important to note that diagnostic time and labor rates at auto repair shops can vary significantly based on factors such as location, vehicle make and model, and engine type. It is advisable to contact local auto repair shops for a more accurate estimate based on your specific circumstances.

What does this mean?

Tech Notes for P0685 2015 GMC Sierra

Check all the Engine Control Module (ECM) fuses, if the fuses are OK, then replacing the ECM relay should take care of the problem.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0685 2015 GMC Sierra Code

1. What does the OBDII code P0685 mean on a 2015 GMC Sierra?

P0685 indicates an issue with the Engine Control Module (ECM) power relay control circuit, specifically that it is open or not functioning correctly.

2. What are the common symptoms of P0685 in a 2015 GMC Sierra?

Common symptoms include difficulty starting the engine, engine stalling, poor performance, or a complete lack of power to the ECM.

3. What causes the P0685 code on a 2015 GMC Sierra?

Possible causes include a faulty ECM power relay, damaged wiring or connectors in the relay circuit, or a malfunctioning ECM.

4. Can I drive my 2015 GMC Sierra with a P0685 code?

Driving with this code is not recommended, as it may lead to engine stalling or failure to start, leaving you stranded.

5. How do I fix the P0685 code on a 2015 GMC Sierra?

Fixes may involve replacing the ECM power relay, repairing damaged wiring or connectors in the circuit, or, in rare cases, replacing the ECM.

6. How can I diagnose the P0685 code on my 2015 GMC Sierra?

Start by inspecting the power relay, wiring, and connectors for damage or corrosion. Use a multimeter to test for proper voltage in the relay circuit.

7. What tools are needed to troubleshoot the P0685 code on a 2015 GMC Sierra?

A digital multimeter, a scan tool capable of reading live data, and basic hand tools are typically needed to diagnose and repair the issue.

8. How much does it cost to fix the P0685 code on a 2015 GMC Sierra?

Repair costs vary depending on the issue. Replacing a power relay may cost $20-$50, while more extensive wiring repairs or ECM replacement could be significantly more.

9. Can a dead battery cause the P0685 code on a 2015 GMC Sierra?

While unlikely, a weak or dead battery may contribute to voltage issues that could trigger this code. Always check the battery and charging system as part of the diagnosis.

10. Is the P0685 code related to any other trouble codes on a 2015 GMC Sierra?

Yes, it may be accompanied by other codes related to the ECM, power relay, or electrical system, such as P0686 or P0687. Always check for and address related codes.

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