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AutoCodes – GMC – P0686 2018 GMC Sierra

P0686 2018 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Low

Quick Answer

The powertrain relay is a normally open relay. Common causes include Weak battery, Low voltage while cranking, Faulty Engine Control Module (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
P0686 2018 GMC Sierra indicates Engine Control Module Power Relay Control Circuit Low.
Common causes
Common causes include Weak battery, Low voltage while cranking, Faulty Engine Control Module (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.
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Code Popularity 150
How popular is this code, among other codes? Low
What is this?
Table of contents Created and updated by William Orellana on Jul 19, 2022
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Code P0686 2018 GMC Sierra Description

The powertrain relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the armature contact at all times. The Engine Control Module (ECM) supplies the ground path to the relay coil control circuit via an internal integrated circuit called an Output Driver Module (ODM). The ODM output control is configured to operate as a low side driver for the powertrain relay. The ODM for the powertrain relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. When the ECM commands the powertrain relay ON, ignition 1 voltage is supplied to the ECM, and to several additional circuits.
OBDII Code P0686 2018 GMC Sierra - Engine Control Module Power Relay Control Circuit Low - AutoCodes.com
P0686 2018 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Low
What does this mean?

What are the Possible Causes of the DTC P0686 2018 GMC Sierra?

  • Weak battery
  • Low voltage while cranking
  • Faulty Engine Control Module (ECM) power relay
  • ECM power relay harness is open or shorted
  • ECM power relay circuit poor electrical connection
  • Blown ECM fuse
  • Faulty ECM

How to Fix the DTC P0686 2018 GMC Sierra?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0686 2018 GMC Sierra code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0686 2018 GMC Sierra code?

Need more information on how to fix the P0686 2018 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0686 2018 GMC Sierra code diagnosed by a professional: Find a repair shop in your area

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 P0686 2018 GMC Sierra Code

1. What does OBDII code P0686 mean on a 2018 GMC Sierra?

P0686 indicates a fault in the Engine Control Module (ECM) Power Relay Control Circuit, specifically that the circuit voltage is too low.

2. What are the common symptoms of code P0686 in a 2018 GMC Sierra?

Symptoms may include the engine not starting, stalling while driving, reduced power, or the Check Engine Light being illuminated.

3. What causes code P0686 in a 2018 GMC Sierra?

Common causes include a faulty ECM power relay, damaged wiring or connectors in the power relay control circuit, a discharged battery, or a malfunctioning ECM.

4. Can a bad battery trigger code P0686 in a GMC Sierra?

Yes, a weak or discharged battery can cause insufficient voltage to the ECM power relay, triggering code P0686.

5. How is OBDII code P0686 diagnosed on a 2018 GMC Sierra?

Diagnosis involves checking the ECM power relay, inspecting wiring and connectors for damage, testing the battery and alternator, and verifying the ECM’s functionality.

6. Can I drive my 2018 GMC Sierra with code P0686?

It’s not recommended, as the engine may stall unexpectedly or fail to start, potentially leaving you stranded.

7. How do you fix code P0686 on a 2018 GMC Sierra?

Repairs may include replacing the ECM power relay, repairing or replacing damaged wiring or connectors, charging or replacing the battery, or replacing the ECM if necessary.

8. How much does it cost to fix code P0686 in a GMC Sierra?

Repair costs can vary but typically range from $50 to $300 for parts and labor, depending on the specific issue.

9. Can a faulty alternator cause code P0686 in a 2018 GMC Sierra?

Yes, a malfunctioning alternator can lead to low voltage, which may affect the ECM power relay circuit and trigger this code.

10. Does clearing the P0686 code fix the issue on a GMC Sierra?

Clearing the code without addressing the root cause will only temporarily remove the error, and the code is likely to return.

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