P205B

Tank Temperature Sensor Circuit Range/Performance

P205B is a generic OBD-II powertrain diagnostic trouble code: Tank Temperature Sensor Circuit Range/Performance. 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
P205B
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P205B means

P205B is an SAE generic powertrain code that sets when the Engine Control Module (ECM) detects that the signal from the reductant (Diesel Exhaust Fluid / DEF) tank temperature sensor is outside the expected range or is behaving inconsistently relative to operating conditions. The reductant temperature sensor monitors the fluid temperature inside the DEF tank so the SCR system can regulate dosing and prevent freezing or overheating of the urea solution.

The code triggers a range/performance fault rather than a hard open/short-circuit fault (P205A/P205C), meaning the signal is present but implausible — for example, the reading does not change with ambient temperature, diverges from coolant temperature under expected warm-up conditions, or drifts outside the sensor's calibrated voltage window.

Because the DEF tank temperature sensor is typically integrated with the DEF pickup tube assembly (level sensor, temperature sensor, and suction tube sold as one unit), replacement usually involves the complete assembly.

Common causes

Most-frequently reported root causes when P205B is logged.

  • 1
    Faulty reductant tank temperature sensor (internal failure or drift)
  • 2
    Corroded, chafed, or open wiring in the sensor signal or ground circuit
  • 3
    Poor electrical connection at the sensor connector (water ingress, terminal push-back)
  • 4
    Contaminated or incorrect DEF fluid degrading sensor element contact
  • 5
    Defective DEF pickup tube assembly (sensor sold as integrated unit)
  • 6
    ECM reference voltage or sensor ground fault
  • 7
    Extreme ambient temperature causing plausibility check failure during cold-start

Symptoms drivers notice

MIL (Check Engine light) illuminated
SCR / DEF system warning light or message on instrument cluster
Inaccurate DEF temperature reading in scan tool live data
Possible DEF dosing interruption or SCR system entering default mode
Potential NOx emissions non-compliance
On commercial vehicles: inducement warning (speed or power derate if fault persists)

How to diagnose P205B

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record all stored DTCs
  2. 2
    Check scan tool live data for the reductant temperature sensor voltage/value at key-on cold
  3. 3
    Perform a visual inspection of the DEF tank sensor wiring harness
  4. 4
    With the connector unplugged, measure sensor resistance across the signal pins against spec
  5. 5
    Check ECM-side reference voltage (typically 5 V) and ground integrity
  6. 6
    Inspect DEF fluid quality (colour, concentration)
  7. 7
    Replace the reductant temperature sensor (or complete DEF pickup tube assembly if integrated)

Vehicles where we've handled P205B

Platforms in our catalogue with confirmed P205B coverage.

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

Related powertrain codes

Frequently asked questions

Can I drive with P205B active?

Short-term driving is generally possible. However, on commercial trucks the fault will escalate to an inducement derate if not repaired within the permitted window.

Is the DEF temperature sensor replaced separately or as an assembly?

On most modern vehicles the temperature sensor is integrated into the DEF pickup tube assembly alongside the level sensor and suction tube. The entire assembly must be replaced as a unit, typically costing $300–$600 in parts plus labour.

Could bad DEF fluid cause P205B?

Yes. Contaminated, diluted, or incorrectly concentrated DEF can deposit urea crystals or other residues on the sensor element.

What is the difference between P205B and P205A or P205C?

P205A denotes a low-voltage fault, P205C denotes a high-voltage fault. P205B specifically indicates a range or performance problem.

Disabling P205B in software

RaceTune can permanently disable P205B — 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 P205B 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 2 software versions
  • 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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