AutoCodes – GMC – P0688 GMC

P0688 GMC Code - Electronic Control Module Power Relay Sense 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: P0688 GMC indicates Electronic Control Module Power Relay Sense 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 1,389

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 May 15, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0688 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 P0688 GMC - Electronic Control Module Power Relay Sense Circuit/Open - AutoCodes.com — P0688 GMC Code - Electronic Control Module Power Relay Sense Circuit/Open

What does this mean?

What are the Possible Causes of the DTC P0688 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 P0688 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 is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0688 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.

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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 P0688 GMC Code

1. What are the common symptoms of OBDII code P0688 in a GMC vehicle?

The common symptoms of P0688 include engine stalling, difficulty starting the vehicle, and illumination of the Check Engine Light.

2. What does the OBDII code P0688 in a GMC indicate?

P0688 indicates a problem with the Electronic Control Module Power Relay Sense Circuit/Open in the vehicle.

3. What are the potential causes of OBDII code P0688 in a GMC?

Possible causes of P0688 include a faulty power relay, damaged wiring or connectors in the power relay circuit, or a malfunctioning Electronic Control Module.

4. How can I diagnose the cause of OBDII code P0688 in my GMC?

Diagnosing P0688 may involve visually inspecting the power relay and related wiring, checking for loose or corroded connections, and using a multimeter to test the relay and circuit for continuity.

5. Can I drive my GMC with OBDII code P0688?

It is not recommended to drive your GMC with an active P0688 code, as it can lead to further damage or safety issues. It's best to address the issue promptly.

6. How can I repair OBDII code P0688 in my GMC?

Repairing P0688 may involve replacing the faulty power relay, repairing damaged wiring or connectors, or replacing the Electronic Control Module if necessary.

7. Are there any tips for preventing OBDII code P0688 in my GMC?

Regularly inspecting and maintaining the power relay and related components, as well as addressing any electrical issues promptly, can help prevent the occurrence of P0688.

8. Can a DIY enthusiast fix OBDII code P0688 in a GMC?

Depending on the skill level and experience of the individual, a DIY enthusiast may be able to diagnose and repair P0688 by following a detailed repair manual or seeking assistance from online resources.

9. How much does it cost to fix OBDII code P0688 in a GMC?

The cost of fixing P0688 can vary depending on the cause of the issue, the parts needed for repair, and whether the repair is done by a professional mechanic or DIY enthusiast.

10. Will resetting the OBDII code P0688 in my GMC make it go away permanently?

Resetting the code may temporarily turn off the Check Engine Light, but if the underlying issue causing P0688 is not addressed, the code is likely to reappear. It's important to diagnose and fix the root cause of the problem.