AutoCodes – Generic – P0688

P0688 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 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 26,196

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
Comments
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Code P0688 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 - Electronic Control Module Power Relay Sense Circuit/Open - AutoCodes.com — P0688 Code - Electronic Control Module Power Relay Sense Circuit/Open

What does this mean?

What are the Possible Causes of the DTC P0688?

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?

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 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 P0688 code?

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Information for Specific Makes

P0688 Audi — Electronic Control Module Power Relay Control Circuit Open
P0688 Buick — Electronic Control Module Power Relay Sense Circuit/Open
P0688 Cadillac — Electronic Control Module Power Relay Sense Circuit/Open
P0688 Chevrolet — Electronic Control Module Power Relay Sense Circuit/Open
P0688 Chrysler — Auto Shutdown Relay Control Circuit Open
P0688 Dodge — Auto Shutdown Relay Control Circuit Open
P0688 Ford — Electronic Control Module Power Relay Sense Circuit/Open
P0688 GMC — Electronic Control Module Power Relay Sense Circuit/Open
P0688 Jeep — Auto Shutdown Relay Control Circuit Open
P0688 Lincoln — Electronic Control Module Power Relay Sense Circuit/Open
P0688 Mercury — Electronic Control Module Power Relay Sense Circuit/Open
P0688 Mitsubishi — Electronic Control Module Power Relay Control Circuit Open
P0688 Pontiac — Electronic Control Module Power Relay Sense Circuit/Open
P0688 Saturn — Electronic Control Module Power Relay Sense Circuit/Open
P0688 Volkswagen — Electronic 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.