P05F5

Symptoms

• Check Engine Light and Emission System Warning Light Illuminates
• Unstable or completely inoperative exhaust aftertreatment system
• Possible relay overheating
• Increased NOx or soot emissions
• Other SCR/DPF system codes

Causes

• Short circuit of the relay control circuit to the power line (+12V)
• Damage to the insulation of the control wire (touching the positive bus)
• Malfunction of the relay itself (internal breakdown of insulation to power supply)
• ECU output transistor malfunction (high output voltage)
• Incorrect connection diagram (repair error)

How to Fix

1. Read codes, fix parameters
2. Disconnect the relay connector, measure the voltage at the control contact with the ignition on
3. If >1V when the ECU is turned off, there is a short circuit in the wiring
4. Check the control wire from the relay to the computer for short circuit to the positive bus
5. Inspect the wiring harness near hot surfaces and positive connections
6. Replace the relay or eliminate the short circuit

Related codes

Error P05F5 by Vehicle Brand