P202A

Tank Heater Control Circuit/Open

P202A is a generic OBD-II powertrain diagnostic trouble code: Tank Heater Control Circuit/Open. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P202A
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P202A means

P202A is set when the ECM or SCR controller detects that the control circuit voltage for the reductant (DEF/AdBlue) pump is lower than the expected minimum threshold when the pump is commanded off, or when the control circuit cannot drive the pump motor to the commanded state. A low-circuit fault typically indicates a short to ground on the pump control or supply wiring.

The reductant pump pressurizes DEF fluid from the tank and delivers it to the reductant injector. If the pump cannot operate correctly, no urea is delivered to the SCR catalyst, and NOx conversion stops. The ECM monitors pump current or voltage feedback to verify proper pump operation, and a sustained low-voltage condition triggers this fault.

Vehicles with emissions derate strategies will begin counting non-compliant operating time once SCR functionality is lost. Depending on OEM calibration and regulatory requirements, a torque or speed derate may engage after a defined period, making this fault more urgent than a simple sensor circuit code. The root cause is usually in the pump wiring, pump module, or the power supply to the DEF pump assembly.

Common causes

Most-frequently reported root causes when P202A is logged.

  • 1
    Short to ground on the reductant pump control or supply wiring.
  • 2
    Failed DEF pump motor with an internal short causing low voltage on the circuit.
  • 3
    Damaged wiring harness with a chafed wire shorting to the vehicle chassis.
  • 4
    Corroded pump connector causing high resistance and low voltage drop.
  • 5
    Faulty SCR/DEF control module output driver.
  • 6
    Blown fuse in the DEF pump supply circuit causing a collapsed voltage.
  • 7
    DEF pump seized due to frozen or crystallized urea pulling excessive current.

Symptoms drivers notice

MIL illuminated along with a DEF or SCR system warning.
No reductant being delivered to the SCR catalyst.
NOx efficiency codes stored as secondary faults.
Possible torque derate or vehicle speed limitation.
DEF pump audibly not operating when commanded.

How to diagnose P202A

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and note companion NOx, SCR efficiency, or DEF level codes.
  2. 2
    Inspect the DEF pump assembly connector and wiring for shorts to ground, chafing, or corrosion.
  3. 3
    Check the fuse and relay for the DEF pump supply circuit.
  4. 4
    Measure voltage at the pump connector with key on and pump commanded on via scan tool.
  5. 5
    Measure current draw of the pump motor; excessive current indicates a seized or shorted pump.
  6. 6
    Perform a continuity check on the control wire from the ECM/SCR module to the pump.
  7. 7
    Replace the DEF pump module if wiring and supply checks are normal but the pump does not operate.

Related powertrain codes

Frequently asked questions

Can frozen DEF cause P202A?

Yes. Frozen DEF can seize the pump, causing it to draw excessive current and collapse the supply voltage, triggering a low-circuit fault.

What is the difference between P202A (circuit low) and an open circuit fault?

A low-circuit fault indicates a short to ground pulling voltage down; an open circuit fault would prevent any current flow at all, typically setting a different code.

Will the DEF pump restart after the fault clears?

Once the root cause is repaired and the code is cleared, the pump should resume normal operation on the next commanded cycle.

How urgent is P202A compared to other DEF codes?

It is among the more urgent DEF codes because it disables the entire dosing system, directly stopping NOx reduction and starting the clock on any emissions derate strategy.

Disabling P202A in software

RaceTune can permanently disable P202A — 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 P202A 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 MD1CP004 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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