AutoCodes – Dodge – P0478 Dodge

P0478 Dodge Code - High Voltage On The Engine Brake Driver

Quick Answer

Exhaust Back Pressure Regulator - Is a variable position valve that controls exhaust back pressure during cold ambient temperatures to increase cab heat and decrease the amount of time needed to defrost the windshield. Common causes include Faulty Engine Brake Driver Relay, Engine Brake Driver harness is open or shorted, Engine Brake Driver circuit poor electrical connection. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

What it means: P0478 Dodge indicates High Voltage On The Engine Brake Driver.
Common causes: Common causes include Faulty Engine Brake Driver Relay, Engine Brake Driver harness is open or shorted, Engine Brake Driver circuit poor electrical connection.
Severity: Moderate - service should be scheduled soon.
Can I drive?: The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

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Code Popularity 3,520

How popular is this code, among other codes? Low

Repair Importance Level

Moderate (Service soon) (2 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Apr 23, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P0478 Dodge Description

Exhaust Back Pressure Regulator - Is a variable position valve that controls exhaust back pressure during cold ambient temperatures to increase cab heat and decrease the amount of time needed to defrost the windshield. The Engine Control Module (ECM) uses the measured exhaust back pressure, (ambient) intake air temperature, engine oil temperature and engine load to determine the desired exhaust back pressure. Valve position is controlled by switching the output signal circuit to 12 volts inside the ECM. On/off time is modulated from 0 to 99 % dependent upon the exhaust back pressure desired.
Upon each initial engine start-up, the ECM exercises the exhaust back pressure valve by commanding it to cycle on and off once. If upon start-up the temperature of intake air sensed by the Intake Air Temperature (IAT) sensor is < 37Â°F (5Â°C) and the oil temperature sensed by the Engine Oil Temperature (EOT) sensor is between 32Â°-140Â°F (0-60Â°C) it will continue to keep the back pressure valve partially closed. As the oil temperature rises during engine operation, the ECM will control the valve in response to the rising oil temperature.

OBDII Code P0478 Dodge - High Voltage On The Engine Brake Driver - AutoCodes.com — P0478 Dodge Code - High Voltage On The Engine Brake Driver

What does this mean?

What are the Possible Causes of the DTC P0478 Dodge?

Faulty Engine Brake Driver Relay
Engine Brake Driver harness is open or shorted
Engine Brake Driver circuit poor electrical connection

How to Fix the DTC P0478 Dodge?

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 P0478 Dodge 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.