AutoCodes – Generic – P2688

P2688 Code - Fuel Heater Relay Control Circuit Low Voltage

Quick Answer

Ignition voltage is supplied to the coil side of the fuel heater relay whenever the ignition is On. Common causes include Faulty Fuel Supply Heater, Fuel Supply Heater harness is open or shorted, Fuel Supply Heater circuit poor electrical connection. 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: P2688 indicates Fuel Heater Relay Control Circuit Low Voltage.
Common causes: Common causes include Faulty Fuel Supply Heater, Fuel Supply Heater harness is open or shorted, Fuel Supply Heater circuit poor electrical connection.
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 10,792

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 Aug 01, 2021

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P2688 Description

Ignition voltage is supplied to the coil side of the fuel heater relay whenever the ignition is On. The Engine Control Module (ECM) provides a ground to control the fuel heater relay. When the ECM is commanding the fuel heater On, the voltage of the control circuit should be low, near 0 V. When the ECM is commanding the fuel heater Off, the voltage of the control circuit should be high, near battery voltage. The Diagnostic Trouble Code (DTC) will be set when the ECM detects the fuel heater relay control circuit is shorted to ground for greater than 1 s.

OBDII Code P2688 - Fuel Heater Relay Control Circuit Low Voltage - AutoCodes.com — P2688 Code - Fuel Heater Relay Control Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P2688?

Faulty Fuel Supply Heater
Fuel Supply Heater harness is open or shorted
Fuel Supply Heater circuit poor electrical connection

How to Fix the DTC P2688?

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 P2688 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 P2688 code?

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Need Help with the Code?

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Information for Specific Makes

P2688 Buick — Fuel Heater Relay Control Circuit Low Voltage
P2688 Cadillac — Fuel Heater Relay Control Circuit Low Voltage
P2688 Chevrolet — Fuel Heater Relay Control Circuit Low Voltage
P2688 GMC — Fuel Heater Relay Control Circuit Low Voltage

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.