P04D5

Symptoms

• Engine brake does not engage when activated
• Malfunction indicator light (Check Engine or MIL) is on
• Reduced braking efficiency on descents
• Possible associated error code P04D6

Causes

• Broken wire in engine brake input circuit
• Short circuit to ground in signal circuit
• Faulty engine brake switch
• Damage to the connector or contacts
• Control module malfunction

How to Fix

1. Read error codes with scanner and record freeze frame data
2. Find the switch and input circuit of the engine brake according to the diagram
3. Check the voltage at the circuit input with a multimeter with the brake on and off
4. Check the integrity of the wire from the switch to the computer
5. Inspect connectors for damage and oxidation
6. Replace the switch if it is faulty
7. Repair open or short circuit in wiring
8. Reset the error and check the system operation

Related codes

Error P04D5 by Vehicle Brand