P205A

Tank Temperature Sensor Circuit

P205A is a generic OBD-II powertrain diagnostic trouble code: Tank Temperature Sensor Circuit. 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
P205A
Group
Powertrain
System
SCR/AdBlue
Severity
Warning (MIL on)
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What P205A means

P205A is set when the PCM/ECM detects that the signal from the reductant (DEF/AdBlue) tank temperature sensor is within the normal electrical range but does not correlate with expected values based on operating conditions or other sensor inputs. The reductant tank temperature sensor monitors fluid temperature to manage SCR dosing and prevent freezing or overheating of the urea solution.

The sensor is typically a negative temperature coefficient (NTC) thermistor submerged in the DEF tank. When the ECM determines the signal is implausible -- for example, reading an impossibly low or high temperature relative to ambient or coolant data -- it flags a rationality fault rather than an out-of-range electrical fault.

Continued operation with this fault active may result in inaccurate dosing of reductant, leading to elevated NOx emissions and potential SCR catalyst efficiency codes. In many applications the system will eventually enter a derate mode if SCR efficiency drops as a consequence.

Common causes

Most-frequently reported root causes when P205A is logged.

  • 1
    Faulty reductant tank temperature sensor (NTC thermistor degraded or failed).
  • 2
    Contaminated or incorrect concentration DEF fluid affecting sensor accuracy.
  • 3
    Wiring harness damage, corrosion, or high resistance in the sensor circuit.
  • 4
    DEF pump module failure causing incorrect temperature readings.
  • 5
    ECM/PCM internal fault or software issue misinterpreting sensor data.
  • 6
    DEF tank heater malfunction causing abnormal fluid temperatures.
  • 7
    Water ingress into the sensor connector causing signal offset.

Symptoms drivers notice

MIL (Check Engine light) illuminated.
SCR system warning lamp or DEF system warning on instrument cluster.
Possible reduced NOx conversion efficiency from the SCR catalyst.
Potential torque derate if SCR efficiency drops sufficiently.
No noticeable drivability issue in early stages of the fault.

How to diagnose P205A

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record all stored DTCs and freeze frame data.
  2. 2
    Check live data for the reductant tank temperature sensor value and compare with ambient temperature at cold start.
  3. 3
    Inspect the DEF tank sensor connector and wiring for corrosion, damage, or moisture intrusion.
  4. 4
    Verify DEF fluid quality and concentration using a refractometer; replace fluid if contaminated.
  5. 5
    Perform a sensor resistance check against the manufacturer temperature-resistance curve.
  6. 6
    Inspect the DEF pump/heater module for faults that could affect temperature readings.
  7. 7
    Replace the reductant tank temperature sensor if all wiring and fluid checks pass and the fault persists.

Vehicles where we've handled P205A

Platforms in our catalogue with confirmed P205A coverage.

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

Related powertrain codes

Frequently asked questions

Can I drive with P205A active?

Short term driving is generally possible, but continued operation risks elevated NOx emissions and a potential torque derate if the SCR system cannot verify proper dosing.

Is P205A the same as a DEF level sensor fault?

No. P205A relates specifically to the temperature sensor circuit performance, not the fluid level sensor.

Will P205A clear itself after repair?

After correcting the root cause the code should clear on the next completed drive cycle, or can be cleared manually with a scan tool.

Could bad DEF fluid cause P205A?

Yes. Incorrect DEF concentration or contaminated fluid can affect the sensor's plausibility check, triggering a range/performance fault.

Disabling P205A in software

RaceTune can permanently disable P205A — 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 P205A 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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