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P0685 2016 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Open

Quick Answer

The P0685 diagnostic trouble code (DTC) for a 2016 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, Damaged wiring or connectors in the power relay circuit, Blown fuse related to the ECM power relay. 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 2016 GMC Sierra indicates Engine Control Module Power Relay Control Circuit Open.
Common causes
Common causes include Faulty ECM power relay, Damaged wiring or connectors in the power relay circuit, Blown fuse related to the ECM power relay.
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 18, 2024
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Code P0685 2016 GMC Sierra Description

The P0685 diagnostic trouble code (DTC) for a 2016 GMC Sierra indicates that there is an issue with the Engine Control Module (ECM) Power Relay Control Circuit being open. The ECM power relay is responsible for supplying power to the ECM, which is the brain of the vehicle's engine management system. When the circuit is open, it means that there is a break in the electrical connection between the power relay and the ECM, leading to a loss of power and communication between the two components.

OBDII Code P0685 2016 GMC Sierra - Engine Control Module Power Relay Control Circuit Open
P0685 2016 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Open

Common Causes of P0685 2016 GMC Sierra

  1. Faulty ECM power relay
  2. Damaged wiring or connectors in the power relay circuit
  3. Blown fuse related to the ECM power relay
  4. Malfunctioning ECM
  5. Corrosion or poor connections in the power relay circuit

Symptoms of P0685 2016 GMC Sierra

  1. Engine misfires or rough idling
  2. Poor acceleration and decreased engine performance
  3. Check Engine Light illuminated on the dashboard
  4. Vehicle stalling or difficulty starting
  5. Issues with transmission shifting or drivability

How to Fix P0685 2016 GMC Sierra

  1. Begin by conducting a thorough inspection of the ECM power relay, wiring, and connectors to identify any visible damage or corrosion.
  2. Test the ECM power relay using a multimeter to determine if it is functioning correctly. Replace the relay if necessary.
  3. Check the fuse related to the ECM power relay and replace it if it is blown.
  4. Inspect the ECM for any signs of damage or malfunction. If needed, replace the ECM with a new unit.
  5. Clear the DTC with a scan tool after completing the repairs and perform a test drive to ensure the issue has been resolved.

Cost to Fix P0685 2016 GMC Sierra

The typical repair costs for addressing the P0685 code on a 2016 GMC Sierra can vary depending on the specific cause of the issue and the parts/labour required. On average, the cost for parts such as an ECM power relay or a new ECM can range from $50 to $300, while labour costs may range from $100 to $300. Overall, the total repair cost could fall between $150 and $600, but it is advisable to obtain a detailed quote from a reputable auto repair shop based on your vehicle's specific needs and location. Keep in mind that diagnostic time and labour rates can vary, so it's recommended to inquire about these factors before proceeding with the repair.

What does this mean?

Tech Notes for P0685 2016 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 2016 GMC Sierra Code

1. What does the OBDII code P0685 mean on a 2016 GMC Sierra?

P0685 indicates an open circuit in the Engine Control Module (ECM) Power Relay Control Circuit, which can prevent the ECM from powering on or functioning properly.

2. What are the common symptoms of code P0685 in a 2016 GMC Sierra?

Symptoms may include the engine failing to start, intermittent stalling, no communication with the ECM during diagnostics, or illuminated check engine light.

3. What causes the P0685 code to appear on a 2016 GMC Sierra?

Common causes include a faulty ECM power relay, damaged or corroded wiring or connectors in the relay circuit, a blown fuse, or, less commonly, a malfunctioning ECM.

4. How do I diagnose the P0685 code on my 2016 GMC Sierra?

Start by inspecting the ECM power relay, fuses, and wiring for damage or corrosion. Use a multimeter to test for voltage and continuity in the circuit. Check for proper relay operation and ensure the ECM is receiving power.

5. Can a bad ECM power relay cause the P0685 code?

Yes, a defective ECM power relay is one of the most common causes of the P0685 code, as it can prevent power from reaching the ECM.

6. Is it safe to drive my 2016 GMC Sierra with a P0685 code?

It is generally not safe to drive with this code, as it can lead to intermittent stalling or prevent the engine from starting altogether.

7. How do I fix the P0685 code on a 2016 GMC Sierra?

Repairs may include replacing a faulty ECM power relay, repairing or replacing damaged wiring or connectors, checking and replacing blown fuses, or addressing ECM issues if necessary.

8. How much does it cost to repair the P0685 code on a 2016 GMC Sierra?

The cost varies depending on the issue. Replacing an ECM power relay typically costs $20–$50 for parts, while wiring repairs or ECM replacement can cost significantly more, depending on labor and parts.

9. Can a weak battery trigger the P0685 code on a 2016 GMC Sierra?

A weak or failing battery could contribute to the code if it leads to insufficient voltage reaching the ECM power relay or circuit.

10. Do I need to reprogram the ECM after fixing the P0685 code on a 2016 GMC Sierra?

Reprogramming is usually not necessary unless the ECM itself is replaced. After repairs, clear the code and perform a test drive to ensure the issue is resolved.

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