P21C7Reductant Control Module Power Relay/Relays Control Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P21C7 flags a break in the control line of the power relay, or group of relays, that supplies the DEF control module and the loads behind it. Ford's 2023 diesel summary evaluates it inside the same continuous heater relay check as P21C2 to P21C4, so on that design the relay also feeds the heating circuits. The code sets within 5 s if the output stage is on but the heater supply reads 0 V, or if the stage is off and voltage is still present, meaning the commanded and the actual relay state disagree. Without supply, DEF heating and possibly dosing stop, and SCR warnings follow. P21C8 and P21C9 are the low and high faults of this line; P20EA and P20EB judge when the relay drops out after the key is turned off.
- What you may notice
- Check engine light on
- DEF heating and dosing do not work
- SCR warning and countdown to restricted starting or speed
- Likely causes
- LikelyRelay defective or missing from its socket
- PossibleOpen control wire or loose terminal between module and relay
- PossibleBlown fuse in the relay or module feed
- RareDriver in the controlling module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €20 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.