AutoCodes – GMC – P0685 2014 GMC Sierra

P0685 2014 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 2014 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 259

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 2014 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 2014 GMC Sierra - Engine Control Module Power Relay Control Circuit Open - AutoCodes.com — P0685 2014 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Open

What does this mean?

What are the Possible Causes of the DTC P0685 2014 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 2014 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 2014 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 2014 GMC Sierra code?

Need more information on how to fix the P0685 2014 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 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 isnâ€™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?

Youâ€™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 doesnâ€™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.