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Home / DTC / P20C2 — Reductant Heater C Control Circuit Performance

P20C2 — Reductant Heater C Control Circuit Performance

Detailed page for trouble code P20C2.

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P20C2

Generic P — Powertrain

Reductant Heater C Control Circuit Performance

Brand: Generic
Type: P — Powertrain
Views: UK: 17 EN: 42 RU: 21
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Page language: EN

Causes

  • Open or shorted wiring in the Heater C circuit
  • Corroded, loose or damaged connector at heater or control module
  • Blown fuse or faulty relay supplying the heater circuit
  • Failed reductant heater element (open or shorted)
  • Failed heater control driver in ECM/BDC/DEF control module
  • High resistance in ground or supply under high load (voltage drop)

Symptoms

  • Malfunction Indicator Lamp (MIL) or DEF system warning illuminated
  • Reduced or disabled DEF/heater operation; possible NOx control fault
  • Warning message about DEF/Reductant system (varies by manufacturer)
  • Possible derate/limp mode if emissions control degraded
  • Unable to reach required reductant temperature for dosing/regeneration

What to check

  • Read freeze frame and DTCs with a capable scan tool; check for related codes
  • Inspect wiring harness and connectors for damage, corrosion, or water
  • Verify appropriate fuse and relay for reductant heater circuit
  • Measure resistance of heater element (with vehicle power off) at the heater connector
  • Backprobe/control output at module while commanding heater ON and monitor voltage/current
  • Check supply voltage and ground integrity during heater command (look for voltage drops)

Signal parameters

  • Commanded state: when ECU commands ON, control circuit will switch the heater to battery voltage or ground (depends on vehicle) — expect switching between ~0 V and near-battery voltage under command
  • Open-circuit heater resistance: typically low ohms (vehicle-specific). An open or very high resistance indicates a failed element.
  • When commanded ON: measurable current flow through the heater; if current is zero or excessive, a fault exists
  • Voltage drop at heater connector under load should be minimal. Significant drop indicates high resistance in wiring/connectors or bad ground
  • Refer to vehicle-specific service data for exact resistance, current draw, and PWM frequency if used

Diagnostic algorithm

  1. Confirm DTC P20C2 and any related codes. Record freeze frame and live data while attempting heater command.
  2. Visually inspect wiring and connectors for Heater C: look for corrosion, broken wires, chafing, melted insulation, or water intrusion.
  3. Check fuses and relays for the reductant heater circuit; replace if blown or faulty and retest.
  4. With ignition OFF, disconnect the heater connector and measure element resistance to ground and between heater terminals. Compare to vehicle data; an open or shorted element indicates replacement.
  5. With a fused jumper or appropriate fused test supply (observe safety procedures), briefly apply battery voltage to the heater terminals to confirm the heater element warms and draws current. Do not leave jumper connected — use proper fusing.
  6. Reconnect and backprobe the control connector at the module. Command the heater ON with a scan tool and measure control output voltage and current flow. Note any PWM behavior or lack of switching.
  7. If there is no output from the module but wiring and heater are good, suspect internal driver fault in control module; verify grounds and supply power to the module before replacement.
  8. Repair or replace any damaged wiring, connectors, fuses, relays or heater assemblies. After repairs clear codes and perform a functional test and monitor for reoccurrence.
  9. If intermittent, perform wiggle tests and rerun guided diagnostics or extended monitoring to capture fault conditions.

Likely causes

  • Wiring harness chafe or broken conductor to Heater C
  • Connector corrosion or pin pushed out at heater plug
  • Blown heater fuse or relay contact failure
  • Heater element failure (short or open)
  • Control module driver transistor failure

Fault status

⚠️ Status
Reductant Heater C Control Circuit Performance — abnormal electrical performance detected in the Heater C control circuit (open/short/high resistance or driver fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P20C0 P20C1 P20C3 P20C4 P20C5 P20C6
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