AutoCodes – GMC – P0685 2015 GMC Sierra

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

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: P0685 2015 GMC Sierra indicates Engine Control Module Power Relay Control Circuit Open.
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 233

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jul 19, 2022

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0685 2015 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 P0685 2015 GMC Sierra - Engine Control Module Power Relay Control Circuit Open - AutoCodes.com — P0685 2015 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Open

What does this mean?

What are the Possible Causes of the DTC P0685 2015 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 P0685 2015 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 does this mean?

Code Tech Notes

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

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0685 2015 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 P0685 2015 GMC Sierra code?

Need more information on how to fix the P0685 2015 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the 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 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.