P05F7: Exhaust Aftertreatment Power Relay Control Circuit Stuck Off

A power relay, switched by the engine module through an output driver, feeds aftertreatment consumers such as the DEF pump, tank and line heaters and possibly NOx sensors or the SCR module. CARB requires such outputs to be checked for circuit faults and function. P05F7 is the opposite function check: the relay does not close although it is commanded on, so the load side stays without voltage. No manufacturer document available to us uses this exact code; GM and Ford monitor the same function under their own codes. If the relay fails, heaters, pump and SCR control drop out and dosing stops.

Symptoms

• Check engine light on
• DEF/AdBlue warning, possibly countdown to no-restart
• Follow-up codes for heaters, pump or NOx sensor supply

Most likely causes

• Relay contacts burnt or coil faulty, relay does not close
• Fuse on the load side blown
• Corroded connector or relay socket
• Output driver in the engine module faulty

What to check, in order

Start with the simplest. You can tick off each step.

1. Look for leaks and visible damage
2. Use the scanner to command the movement and compare the actual position with the requested one.
3. Check the connectors and wires near the exhaust
4. Check the live data
5. Test the actuator with the scanner

Good to know

• Repair difficulty: easy
• It can trigger limp mode.
• It affects emissions.

What each character of P05F7 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 5: Speed and idle
• F7: Specific fault in that system

Frequently asked questions

Can I keep driving with code P05F7?

You can usually keep driving in the short term. If you smell exhaust fumes in the cabin, stop driving and ventilate the car.

What causes code P05F7?

The most common causes are: relay contacts burnt or coil faulty, relay does not close; fuse on the load side blown; corroded connector or relay socket.

Related codes

• P21C2Reductant Heater Relay Control Circuit/Open
• P21C3Reductant Heater Relay Control Circuit Low
• P21C4Reductant Heater Relay Control Circuit High
• P21C7Reductant Control Module Power Relay/Relays Control Circuit/Open
• P20EAReductant Control Module Power Relay De-Energized Performance - Too Early
• P20EBReductant Control Module Power Relay De-Energized Performance - Too Late

Sources

• law.cornell.edu: 13 CCR 1968.2
• fordservicecontent.com: obd summary diesel 2023
• data.epo.org: document

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.