Technical Description of OBD-II Trouble Code
The circuit for the Reductant Tank Temperature Sensor is registering a high voltage.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to many OBD-II vehicles (1996-newer), including Mercedes, Sprinter, Ford, GMC, Chevrolet, etc. The specific repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P205D indicates that the powertrain control module (PCM) has detected excessive voltage in the reductant tank temperature sensor circuit. This code is found exclusively in vehicles with clean burning diesel engines.
The catalyst system is responsible for reducing all exhaust emissions, although some applications also have a NOx trap.
Exhaust gas recirculation (EGR) systems further reduce NOx emissions. However, larger and more powerful diesel engines cannot meet strict U.S. emission standards with just the EGR, diesel particulate filter/catalytic converter, and NOx trap. This led to the development of selective catalytic reduction (SCR) systems.
SCR systems inject a reductant compound or diesel exhaust fluid (DEF) into the exhaust system before the diesel particulate filter, NOx trap, and/or catalytic converter. The precise injection of DEF raises the temperature of the filtration element, improving its efficiency and longevity. It also reduces harmful exhaust emissions. The entire SCR system is monitored and controlled by the PCM or a stand-alone controller. The controller monitors various sensors, including O2, NOx, and exhaust temperature sensors, to determine the optimal time for DEF injection. Accurate DEF injection is crucial for maintaining acceptable exhaust temperature and optimizing pollutant filtration.
The reductant/regeneration supply pump pressurizes the DEF in the liquid reductant system when needed. The PCM monitors the supply pump voltage for consistent fluctuation and load percentage. It also monitors pressure sensors in the reductant supply system to detect any leaks.
If the PCM detects excessive voltage in the reductant tank temperature sensor circuit, a code P205D is stored and the malfunction indicator lamp (MIL) may illuminate. Multiple ignition cycles with a failure may be required for MIL illumination.
Example of a DEF reductant tank:
What is the severity of this DTC?
A stored code P205D should be considered severe and addressed as quickly as possible. It could disable the SCR system and potentially cause catalyst damage if the underlying conditions are not resolved promptly.
What are some of the symptoms of the code?
Symptoms of a P205D trouble code may include:
What are some of the common causes of the code?
Possible causes for this code include:
What are some P205D troubleshooting steps?
To diagnose a code P205D, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and vehicle-specific diagnostic information.
Refer to your vehicle information source to find a technical service bulletin (TSB) that matches your vehicle’s year, make, model, engine size, stored codes, and symptoms. A TSB may provide helpful diagnostic information.
Use the scanner to retrieve all stored codes and freeze frame data. Write down this information before clearing the codes and then test-drive the vehicle until the PCM enters readiness mode or the code is reset.
If the PCM enters readiness mode, the code is intermittent and may be more challenging to diagnose. In this case, the underlying conditions may need to worsen before an accurate diagnosis can be made.
If the code is immediately reset, consult your vehicle information source for diagnostic flowcharts, connector pin-out charts, connector face views, and component testing procedures/specifications.
Step 1
Use the DVOM to test the reductant temperature sensor according to the manufacturer’s specifications. Consider any components that do not test within the maximum allowable parameters as defective.
Step 2
If the actual reductant temperature is within specifications, the code P205D persists, and the sensor is functioning correctly, use the DVOM to test the input and output signal circuits between the temperature sensor and the PCM/SCR controller. Disconnect all controllers before conducting the DVOM tests.
