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DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P205B

P205BReductant Tank Temperature Sensor A Circuit Range/Performance

P205B indicates that the powertrain control module (PCM) has detected an out-of-range or erratic signal from the reductant tank temperature sensor 'A' circuit, which monitors the temperature of the diesel exhaust fluid (DEF) tank. The PCM compares this sensor's voltage to expected values and flags the code when the reading falls outside the normal operating range or behaves inconsistently.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms.
  • A driver information message warning of reductant system malfunction or low DEF quality.
  • Possible reduction in engine power or torque as the PCM enters limp mode to protect the emissions system.
  • Inaccurate or erratic DEF level and temperature readings on the dashboard gauge.
  • Difficulty starting the engine in extreme cold if the tank heater strategy is affected.
  • Increased diesel exhaust fluid consumption or failure to meet emissions compliance.

Common causes, most likely first

  1. Faulty reductant tank temperature sensor 'A' (open, shorted, or out-of-range).
  2. Damaged or corroded wiring harness or connector at the sensor or PCM.
  3. Poor electrical connection due to water intrusion or debris in the connector.
  4. Failed DEF tank heater element causing the sensor to read implausibly low temperatures.
  5. PCM software issue or internal fault in the temperature sensing circuit.
  6. Contaminated or degraded DEF fluid altering the thermal properties and sensor response.
  7. Extreme ambient temperatures exceeding the sensor's designed operating range.

How to diagnose and fix it

  1. Use a scan tool to retrieve all stored codes and freeze-frame data, then verify the P205B is active and not a history code.
  2. Visually inspect the reductant tank temperature sensor, its wiring, and connectors for damage, corrosion, or loose pins.
  3. Measure the sensor's resistance with a multimeter and compare it to the manufacturer's temperature-resistance chart to confirm sensor accuracy.
  4. Check the DEF tank heater circuit for proper operation, as a failed heater can cause the temperature sensor to read out of range.
  5. Perform a voltage drop test on the sensor signal and ground circuits to rule out high resistance in the wiring.
  6. If the sensor and wiring test good, reflash or update the PCM software to address known calibration issues.
  7. Replace the reductant tank temperature sensor if it fails electrical testing, then clear the code and verify the repair with a test drive.

What the DEF tank sensor code hides

  • A failed DEF tank heater often sets P205B because the temperature sensor reads the tank as colder than it actually is, leading to an implausible range error.
  • Corroded pins in the sensor connector are a frequent cause that visual inspection alone can miss; always perform a pin drag test and check for water intrusion.
  • The code can be set by a software glitch in the PCM that misinterprets a normal sensor signal, so a reflash may be required even after all hardware checks pass.
  • After replacing the sensor, the DEF tank may need to be drained and refilled with fresh fluid to prevent contamination from affecting the new sensor's readings.
  • P205B is often accompanied by other reductant system codes, so diagnosing it in isolation can lead to a misrepair if the root cause is elsewhere in the DEF system.

Can I keep driving with P205B?

You can generally continue driving with P205B, but avoid long trips or heavy loads until the fault is repaired, as the PCM may eventually limit engine power or disable the DEF system, leading to emissions non-compliance and potential limp mode.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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