P20C2

Reductant Heater C Control Circuit Performance

P20C2 is a generic OBD-II powertrain diagnostic trouble code: Reductant Heater C Control Circuit Performance. It is logged by the engine control unit when the scr/adblue monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P20C2
Group
Powertrain
System
SCR/AdBlue
Severity
Warning (MIL on)
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What P20C2 means

P20C2 is the complement to P20C1 and is set when the ECM or aftertreatment module detects a higher-than-expected voltage or open-circuit condition on the Bank 1 reductant injector control circuit. An open circuit prevents the injector solenoid from energising, completely disabling DEF dosing on that bank.

Common causes include an open wire in the injector supply or control circuit, a failed-open injector solenoid, a disconnected or broken connector pin, or an open-circuit driver inside the control module. Because dosing is halted, NOx conversion in the SCR catalyst stops and tail-pipe emissions increase significantly.

The diagnostic approach mirrors P20C1 but focuses on open-circuit checks: verify supply voltage arrives at the injector connector, measure injector solenoid resistance for an open winding, and inspect connector pins for spread, corrosion, or pullback. If the injector and harness are intact, the control module driver circuit should be evaluated last, as module faults are less common than wiring or injector failures.

Common causes

Most-frequently reported root causes when P20C2 is logged.

  • 1
    Open circuit in the reductant injector supply or control wiring.
  • 2
    Failed-open reductant injector solenoid coil.
  • 3
    Loose, corroded, or backed-out pin in the injector connector.
  • 4
    Broken wire inside the harness loom near a flex point.
  • 5
    Open-circuit driver transistor inside the aftertreatment control module.
  • 6
    Blown fuse in the reductant injector supply circuit.

Symptoms drivers notice

MIL or SCR/AdBlue warning lamp illuminated.
DEF dosing stopped, resulting in elevated NOx emissions.
Engine power derate may occur after extended SCR non-compliance.
No immediate driveability impact in mild cases.

How to diagnose P20C2

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record all DTCs and freeze-frame data.
  2. 2
    Check fuses associated with the reductant injector supply circuit.
  3. 3
    Inspect the injector wiring harness and connector for broken wires or damaged pins.
  4. 4
    With the injector disconnected, measure solenoid coil resistance; an open reading confirms injector failure.
  5. 5
    With the injector disconnected, verify supply voltage is present at the harness connector with ignition on.
  6. 6
    Check for continuity from the module driver pin to the injector connector to locate any open wire.
  7. 7
    Replace the injector if the solenoid is open; repair wiring if the fault is in the harness.

Vehicles where we've handled P20C2

Platforms in our catalogue with confirmed P20C2 coverage.

AUDI A4 20D

Related powertrain codes

Frequently asked questions

What is the difference between P20C1 and P20C2?

P20C1 is a circuit low (short to ground or excessive current) fault while P20C2 is a circuit high (open circuit or loss of ground return) fault on the same injector.

Can a corroded connector cause P20C2?

Yes. Corrosion increases circuit resistance to the point of an effective open circuit and is a common cause, especially on vehicles in salt-belt climates.

Will the SCR system recover automatically after repair?

After repairing the circuit and clearing the DTC, the SCR system should resume normal closed-loop dosing on the next drive cycle; confirm with live data.

Is P20C2 only on diesel vehicles?

The code applies to any SCR-equipped vehicle, including some large gasoline engines, but it is most common on diesel-powered vehicles.

Disabling P20C2 in software

RaceTune can permanently disable P20C2 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECUs with a P20C2 disable in our catalogue

Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.

  • Bosch EDC17C74 verified 1 software version

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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