AutoCodes – GMC – P0685 GMC

P0685 GMC 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 GMC 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 4,825

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 GMC 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 GMC - Engine Control Module Power Relay Control Circuit Open - AutoCodes.com — P0685 GMC Code - Engine Control Module Power Relay Control Circuit Open

What does this mean?

What are the Possible Causes of the DTC P0685 GMC?

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 GMC?

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 GMC 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 GMC code?

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

Need Help with the Code?

Get the P0685 GMC code diagnosed by a professional: Find a repair shop in your area

Information for Specific GMC Models

P0685 2014 GMC Sierra — Engine Control Module Power Relay Control Circuit Open
P0685 2015 GMC Sierra — Engine Control Module Power Relay Control Circuit Open
P0685 2016 GMC Sierra — Engine Control Module Power Relay Control Circuit Open
P0685 2017 GMC Sierra — Engine Control Module Power Relay Control Circuit Open
P0685 2018 GMC Sierra — Engine Control Module Power Relay Control Circuit Open

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 GMC Code

1. What are common symptoms of OBDII code P0685 in a GMC vehicle?

- Common symptoms include engine stalling, difficulty starting the engine, and a check engine light illuminated on the dashboard.

2. What does the OBDII code P0685 GMC indicate?

- The code P0685 indicates a malfunction in the Engine Control Module (ECM) power relay control circuit, specifically an open circuit.

3. What are potential causes of the P0685 code in a GMC vehicle?

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

4. How can I diagnose the cause of the P0685 code in my GMC vehicle?

- To diagnose the issue, you can perform a visual inspection of the relay and related wiring, test the relay for continuity, and use a multimeter to check for proper voltage in the circuit.

5. What are some repair tips for fixing the P0685 code in a GMC vehicle?

- Repair options may include replacing the ECM power relay, repairing or replacing damaged wiring or connectors, or replacing the ECM itself if deemed faulty.

6. Can driving with the P0685 code present cause further damage to the vehicle?

- Continuing to drive with the P0685 code present can potentially cause further damage to the engine control system and may lead to more severe issues over time.

7. Is it safe to clear the P0685 code and continue driving without addressing the underlying problem?

- Clearing the code without addressing the underlying issue is not recommended, as the problem will likely persist and could potentially worsen, leading to more significant repairs.

8. How much does it typically cost to repair the P0685 code in a GMC vehicle?

- The cost of repair can vary depending on the specific cause of the issue, but it may range from around $100 to $500 or more, including parts and labor.

9. Can I fix the P0685 code in my GMC vehicle myself, or should I seek professional help?

- While some DIY enthusiasts may be able to diagnose and repair the issue themselves, it is often recommended to seek professional help, especially if you are not experienced with automotive electrical systems.

10. How long does it usually take to resolve the P0685 code in a GMC vehicle?

- The repair time can vary depending on the extent of the issue and the availability of parts, but it typically takes a few hours to a full day to diagnose and fix the problem.