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Home / DTC / P20FC — Reductant Pump B Control Circuit Low

P20FC — Reductant Pump B Control Circuit Low

Detailed page for trouble code P20FC.

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Code

P20FC

Generic P — Powertrain

Reductant Pump B Control Circuit Low

Brand: Generic
Type: P — Powertrain
Views: UK: 16 EN: 28 RU: 17
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Page language: EN

Causes

  • Blown fuse or open power feed to reductant pump B
  • Damaged, corroded or disconnected connector at the pump or ECU
  • Short to ground in the pump control wiring
  • Failed reductant pump motor (internal short or low resistance)
  • Faulty relay or driver module that supplies the pump
  • Poor ground connection for the pump circuit

Symptoms

  • MIL (Malfunction Indicator Lamp) or DEF system warning on dash
  • Service messages related to SCR/DEF system or inhibited regeneration
  • Reduced or no reductant dosing, possible increased NOx emissions
  • Engine may limit regeneration or enter restricted operation depending on vehicle logic
  • Noise or no operation when pump is commanded (if pump fails)

What to check

  • Read and record all related codes and freeze-frame data with a scan tool; check for multiple DEF-related codes
  • Visually inspect pump B connector, wiring harness, and chassis grounds for corrosion, damage or looseness
  • Check fuse(s) and relays associated with reductant pump B
  • Backprobe pump connector with ignition ON and while commanding pump to run; observe supply and control pins
  • Measure voltage at pump supply pin relative to battery ground with key ON and while pump is commanded
  • Measure resistance of the pump motor with connector disconnected (compare to service spec)

Signal parameters

  • Supply (battery) feed at pump: near battery voltage with ignition ON and/or when pump is commanded (approx. 12 V nominal)
  • Control/driver pin: expected to switch between ground and open or be PWM-modulated by ECM; when commanded ON expect switching activity rather than a steady low-voltage fault
  • Pump motor resistance (typical DC motor): low ohms (a few ohms) — should not be open or near short to ground; consult vehicle spec for exact value
  • Pump current draw when running: moderate (typically 1–10 A depending on pump design) — abnormally low or zero current indicates open circuit, very high current indicates short or seized motor
  • PWM frequency (if used): depends on manufacturer (commonly tens to hundreds of Hz); verify with oscilloscope if needed

Diagnostic algorithm

  1. Retrieve all DTCs and freeze-frame data; note conditions when P20FC set.
  2. Visually inspect pump B, connectors, and harness for damage, corrosion, insect/nest intrusion, or water ingress.
  3. Check fuses and relays for the DEF/reductant pump circuit; replace any blown fuses and test relay operation.
  4. With connector connected, backprobe and measure: a) supply pin voltage (should be ~battery voltage when commanded and/or with ignition ON if feed is fused hot); b) control pin behavior while commanding pump on with a scan tool (look for PWM or switching).
  5. If control pin is low at all times, inspect wiring for short to ground between pump and ECM; if control pin is open/high, inspect power feed and fuses.
  6. Disconnect pump and measure motor resistance and insulation; compare to spec. If motor is open or shows shorted windings, replace pump.
  7. Apply fused bench power directly to the pump (temporary, bench test) to confirm pump runs and to measure current draw. Follow safety: fuse, secure wiring, and keep hands away from moving parts.
  8. Perform continuity/short-to-ground tests on the control and power wires between pump connector and ECM; repair wiring as required.
  9. If wiring and pump test good, suspect ECM driver fault—verify with OEM procedures before replacing ECM; replacement is last resort.
  10. After repair, clear DTCs and perform active test or road test to confirm proper pump operation and that the code does not return.

Likely causes

  • Blown fuse or relay for reductant pump B
  • Corroded/disconnected pump connector or wiring harness damage
  • Failed pump motor (does not draw expected current or is open/short)
  • Ground wire loose or high resistance at chassis/engine ground
  • Faulty ECM output transistor on the pump control channel

Fault status

⚠️ Status
Control circuit for Reductant Pump B reads low voltage (circuit below expected range). Possible open feed, short to ground, bad pump, poor ground, or ECM driver issue.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 2.5 hours

Similar codes

P20F8 P20F9 P20FA P20FB P20FD
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