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Engine-Codes – GMC – P0685 2014 GMC Sierra

P0685 2014 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Open

Quick Answer

The P0685 code indicates a problem with the Engine Control Module (ECM) power relay control circuit in a 2014 GMC Sierra. Common causes include Faulty engine control module (ECM) power relay, Damaged or corroded wiring in the power relay circuit, Poor electrical connections or loose terminals affecting the relay operation. 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 2014 GMC Sierra indicates Engine Control Module Power Relay Control Circuit Open.
Common causes
Common causes include Faulty engine control module (ECM) power relay, Damaged or corroded wiring in the power relay circuit, Poor electrical connections or loose terminals affecting the relay operation.
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 Oct 07, 2024
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Code P0685 2014 GMC Sierra Description

The P0685 code indicates a problem with the Engine Control Module (ECM) power relay control circuit in a 2014 GMC Sierra. This code is triggered when the power relay that supplies voltage to the ECM is detected to be open or malfunctioning. The ECM is a critical component of the vehicle's engine management system, responsible for monitoring and controlling various engine functions, including fuel injection, ignition timing, and emissions control. When the power relay circuit is open, the ECM may not receive the necessary power to operate, leading to significant performance issues.

OBDII Code P0685 2014 GMC Sierra - Engine Control Module Power Relay Control Circuit Open
P0685 2014 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Open

Common Causes of P0685 2014 GMC Sierra

  1. Faulty engine control module (ECM) power relay.
  2. Damaged or corroded wiring in the power relay circuit.
  3. Poor electrical connections or loose terminals affecting the relay operation.
  4. Malfunctioning ECM that fails to control the power relay properly.
  5. Blown fuses associated with the ECM power supply circuit.

Symptoms of P0685 2014 GMC Sierra

  1. Engine cranking but failing to start.
  2. Intermittent stalling while driving.
  3. Poor engine performance, including reduced power and acceleration.
  4. Dashboard warning lights illuminated, particularly the check engine light.
  5. Inconsistent or erratic engine behavior, such as misfires or rough idling.

How to Fix P0685 2014 GMC Sierra

  1. Inspect the Relay: Begin by checking the ECM power relay for proper operation. Replace it if it is found to be faulty.
  2. Examine Wiring and Connectors: Inspect the wiring harness and connectors associated with the relay for any signs of damage, corrosion, or loose connections. Repair or replace as necessary.
  3. Check Fuses: Verify that all related fuses are intact and functioning. Replace any blown fuses that could affect the power supply to the ECM.
  4. Test the ECM: If the relay and wiring are in good condition, test the ECM to ensure it is functioning correctly. This may involve using a diagnostic scanner to check for additional codes or performing a bench test.
  5. Clear Codes and Test Drive: After repairs, clear the diagnostic trouble codes and take the vehicle for a test drive to ensure the issue has been resolved and that the vehicle operates normally.

Cost to Fix P0685 2014 GMC Sierra

The cost to repair a P0685 code can vary widely based on the specific issue, labor rates, and parts needed. On average, the total cost for diagnosing and repairing this issue may range from $150 to $600. This estimate includes the price of parts, such as a new relay (typically $20 to $50), and labor costs, which can vary from $80 to $150 per hour. Factors such as location, the complexity of the repair, and the specific make and model of the vehicle can influence the final cost. In metropolitan areas or at dealerships, labor rates may be higher, while independent shops often offer more competitive pricing. It is advisable to consult local repair shops for a more precise estimate based on your specific circumstances.

What does this mean?

Tech Notes for P0685 2014 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.

Need more information about the P0685 2014 GMC Sierra code?

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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 2014 GMC Sierra Code

1. What does the OBDII code P0685 mean on a 2014 GMC Sierra?

P0685 indicates an "Engine Control Module Power Relay Control Circuit Open," meaning the ECM isn't receiving power due to an issue in the relay control circuit.

2. What are the common symptoms of the P0685 code in a 2014 GMC Sierra?

Symptoms may include the engine failing to start, stalling while driving, a lack of communication with the ECM, or the Check Engine Light being illuminated.

3. What causes the P0685 code to appear on a 2014 GMC Sierra?

Common causes include a faulty ECM power relay, damaged or corroded wiring, a blown fuse, or a malfunctioning ECM.

4. Can I drive my 2014 GMC Sierra with the P0685 code?

Driving with this code isn’t recommended, as the engine may stall or fail to start, potentially leaving you stranded.

5. How do I diagnose a P0685 code on a 2014 GMC Sierra?

Start by checking the ECM power relay, inspecting related fuses, and examining the wiring for damage or corrosion. Use a multimeter to test for proper voltage.

6. How do I fix the P0685 code on a 2014 GMC Sierra?

Repairs may include replacing the ECM power relay, repairing or replacing damaged wiring, replacing blown fuses, or in rare cases, replacing the ECM.

7. What tools are needed to diagnose and fix the P0685 code?

You’ll need a multimeter, a scan tool, and possibly a service manual for your 2014 GMC Sierra to locate circuit diagrams and relay positions.

8. How much does it cost to repair the P0685 code on a 2014 GMC Sierra?

Costs can vary, but replacing an ECM power relay typically ranges from $20 to $50 for parts, while professional diagnosis and repair may cost $100 to $300 depending on labor rates.

9. Can a weak battery cause the P0685 code on a 2014 GMC Sierra?

Yes, a weak or failing battery can cause voltage issues, potentially leading to the P0685 code if the ECM doesn’t receive enough power.

10. Does the P0685 code always mean the ECM is faulty?

No, the ECM is rarely the cause. The issue is more likely with the relay, wiring, or fuses. Always perform thorough diagnostics before replacing the ECM.

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