Damaged or corroded wiring harness between the reductant pump and the control module; Failed reductant pump B due to internal electrical fault; Blown fuse or faulty relay supplying power to the reductant pump circuit; Poor electrical connection at the pump connector or control module; Short to ground in the control circuit wiring; Faulty powertrain control module (rare but possible)

DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P20FC

P20FCReductant Pump B Control Circuit Low

Q: What does code P20FC mean?

Reductant Pump B Control Circuit Low. P20FC indicates that the powertrain control module has detected a low-voltage condition on the control circuit for reductant pump B, which is part of the diesel exhaust fluid injection system. The computer monitors the circuit for expected voltage and flags this code when the signal falls below the acceptable threshold, typically indicating a short to ground or an open circuit.

P20FC indicates that the powertrain control module has detected a low-voltage condition on the control circuit for reductant pump B, which is part of the diesel exhaust fluid injection system. The computer monitors the circuit for expected voltage and flags this code when the signal falls below the acceptable threshold, typically indicating a short to ground or an open circuit.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
A message on the dashboard indicating low diesel exhaust fluid or a fault in the emissions system
Reduced engine power or limp mode in some vehicles as a protective measure
Increased diesel exhaust fluid consumption if the pump is commanded to run continuously
Difficulty starting the engine or rough running in extreme cases due to emissions system shutdown

Common causes, most likely first

Damaged or corroded wiring harness between the reductant pump and the control module
Failed reductant pump B due to internal electrical fault
Blown fuse or faulty relay supplying power to the reductant pump circuit
Poor electrical connection at the pump connector or control module
Short to ground in the control circuit wiring
Faulty powertrain control module (rare but possible)

How to diagnose and fix it

Check the fuse and relay for the reductant pump circuit and replace if blown or faulty
Inspect the wiring harness and connectors at the pump and control module for damage, corrosion, or loose pins
Measure resistance and voltage on the control circuit to identify opens or shorts
Perform a bidirectional test of the reductant pump using a scan tool to confirm operation
If the circuit tests good, replace the reductant pump
Clear the code and verify the repair with a test drive

Common Misdiagnosis Traps for P20FC

A low voltage code on the reductant pump control circuit is often caused by a chafed wire near the pump mounting bracket, which can be missed if only the pump itself is inspected.
Technicians sometimes replace the reductant pump without checking the ground connection for the pump module, which can cause a low voltage signal on the control circuit.
The code can be set by a weak battery or charging system issue that causes a momentary voltage drop, so always verify battery condition before condemning the pump.
On some vehicles, the reductant pump control circuit is shared with other emissions components, and a fault in a related circuit can trigger P20FC as a secondary code.

Can I keep driving with P20FC?

You can usually continue driving with this code, but the vehicle may enter limp mode or fail emissions testing. Avoid long trips and schedule a diagnosis soon to prevent further emissions system damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.