P205C

Tank Temperature Sensor Circuit Low

P205C is a generic OBD-II powertrain diagnostic trouble code: Tank Temperature Sensor Circuit Low. 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
P205C
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P205C means

P205C is stored when the PCM/ECM detects that the voltage signal from the reductant (DEF/AdBlue) tank temperature sensor is above the expected maximum threshold. For a typical NTC thermistor circuit, an excessively high voltage on the signal wire indicates a very low or open-circuit resistance condition, which the ECM interprets as an implausibly low temperature reading.

Common electrical causes include an open circuit in the sensor itself, a broken or corroded signal wire between the sensor and ECM, or a loss of the sensor ground reference. Unlike a rationality fault (P205A), this code indicates an electrical boundary violation -- the signal has exceeded the calibrated high-voltage limit rather than being merely implausible.

The SCR dosing system may default to a fixed dosing strategy or suspend dosing while this fault is active, potentially causing elevated NOx output. Prolonged operation without correction can trigger NOx efficiency codes and derate conditions depending on vehicle calibration.

Common causes

Most-frequently reported root causes when P205C is logged.

  • 1
    Open circuit in the reductant tank temperature sensor element.
  • 2
    Broken or corroded signal wire between sensor and ECM.
  • 3
    Loss of sensor ground (high resistance or open ground path).
  • 4
    Damaged DEF pump module connector causing signal line to float high.
  • 5
    ECM input circuit fault causing misread of sensor voltage.
  • 6
    Sensor connector fully unplugged or terminal backed out.
  • 7
    Wiring harness chafing exposing signal wire to an open circuit condition.

Symptoms drivers notice

MIL illuminated on the instrument cluster.
DEF or SCR system warning indicator active.
Possible inaccurate reductant dosing or suspended dosing.
Potential NOx efficiency DTC stored as a secondary fault.
No significant drivability change initially.

How to diagnose P205C

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and note any related SCR or NOx efficiency codes stored alongside P205C.
  2. 2
    Inspect the DEF tank temperature sensor connector for unplugged, backed-out, or corroded terminals.
  3. 3
    Measure the sensor signal voltage at the connector with ignition on; a high or near-reference voltage suggests an open circuit.
  4. 4
    Perform a continuity check on the sensor signal and ground wires back to the ECM.
  5. 5
    Measure sensor resistance directly at the sensor and compare against the manufacturer specification.
  6. 6
    Repair any open circuits or replace the sensor if it reads open internally.
  7. 7
    Clear codes and verify repair with a full drive cycle.

Vehicles where we've handled P205C

Platforms in our catalogue with confirmed P205C coverage.

AUDI A4 20D
AUDI A6
2015
AUDI A7 30D
AUDI A6 30D
2015
AUDI A7

Related powertrain codes

Frequently asked questions

What voltage is considered 'high' for this sensor?

The exact threshold is calibration-specific, but most NTC thermistor circuits flag high voltage when the signal exceeds approximately 4.8-4.9 V, indicating near-open-circuit resistance.

Can P205C be caused by a bad DEF pump module?

Yes. The temperature sensor is often integrated into or connected through the DEF pump module assembly, and a faulty module can break the sensor circuit.

Will the SCR system stop working with P205C active?

Many systems will suspend or limit reductant dosing to protect the SCR catalyst from incorrect dosing, which can lead to secondary NOx efficiency codes.

Is the temperature sensor replaceable separately from the DEF pump?

On some vehicles the sensor is a standalone serviceable part; on others it is integrated into the DEF pump/heater module and requires module replacement.

Disabling P205C in software

RaceTune can permanently disable P205C — 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 P205C 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
  • Bosch EDC17CP44 verified 1 software version
  • 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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