AutoCodes – GMC – P0685 2016 GMC Sierra

P0685 2016 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 2016 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 177

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 2016 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 2016 GMC Sierra - Engine Control Module Power Relay Control Circuit Open - AutoCodes.com — P0685 2016 GMC Sierra Code - Engine Control Module Power Relay Control Circuit Open

What does this mean?

What are the Possible Causes of the DTC P0685 2016 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 2016 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 2016 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 2016 GMC Sierra code?

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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 2016 GMC Sierra Code

1. What does the OBDII code P0685 mean on a 2016 GMC Sierra?

P0685 indicates an open circuit in the Engine Control Module (ECM) Power Relay Control Circuit, which can prevent the ECM from powering on or functioning properly.

2. What are the common symptoms of code P0685 in a 2016 GMC Sierra?

Symptoms may include the engine failing to start, intermittent stalling, no communication with the ECM during diagnostics, or illuminated check engine light.

3. What causes the P0685 code to appear on a 2016 GMC Sierra?

Common causes include a faulty ECM power relay, damaged or corroded wiring or connectors in the relay circuit, a blown fuse, or, less commonly, a malfunctioning ECM.

4. How do I diagnose the P0685 code on my 2016 GMC Sierra?

Start by inspecting the ECM power relay, fuses, and wiring for damage or corrosion. Use a multimeter to test for voltage and continuity in the circuit. Check for proper relay operation and ensure the ECM is receiving power.

5. Can a bad ECM power relay cause the P0685 code?

Yes, a defective ECM power relay is one of the most common causes of the P0685 code, as it can prevent power from reaching the ECM.

6. Is it safe to drive my 2016 GMC Sierra with a P0685 code?

It is generally not safe to drive with this code, as it can lead to intermittent stalling or prevent the engine from starting altogether.

7. How do I fix the P0685 code on a 2016 GMC Sierra?

Repairs may include replacing a faulty ECM power relay, repairing or replacing damaged wiring or connectors, checking and replacing blown fuses, or addressing ECM issues if necessary.

8. How much does it cost to repair the P0685 code on a 2016 GMC Sierra?

The cost varies depending on the issue. Replacing an ECM power relay typically costs $20â€“$50 for parts, while wiring repairs or ECM replacement can cost significantly more, depending on labor and parts.

9. Can a weak battery trigger the P0685 code on a 2016 GMC Sierra?

A weak or failing battery could contribute to the code if it leads to insufficient voltage reaching the ECM power relay or circuit.

10. Do I need to reprogram the ECM after fixing the P0685 code on a 2016 GMC Sierra?

Reprogramming is usually not necessary unless the ECM itself is replaced. After repairs, clear the code and perform a test drive to ensure the issue is resolved.