Technical Description of OBD-II Trouble Code
The control circuit for the reductant tank heater is experiencing low 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 Volkswagen, Mercedes-Benz, Dodge, Audi, and others. The specific repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P202B indicates that the powertrain control module (PCM) has detected insufficient voltage in the control circuit for the reductant tank heater.
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 is why selective catalytic reduction (SCR) systems were invented.
SCR systems inject a reductant compound or diesel exhaust fluid (DEF) into the exhaust before the diesel particulate filter, NOx trap, and/or catalytic converter using the reductant injection valve (solenoid). The precise timing of DEF injection increases the temperature of the filtration element, allowing it to function more efficiently. This improves the longevity of the filtration element and reduces harmful exhaust emissions. The entire SCR system is monitored and controlled by the PCM or a stand-alone controller, which interacts with the PCM. The controller monitors O2, NOx, and exhaust temperature sensors, among other inputs, to determine the optimal time for DEF injection. Precise DEF injection is necessary to maintain acceptable exhaust temperature and optimize pollutant filtration.
Reductant tank heaters are used to prevent diesel exhaust fluid from freezing in extremely cold temperatures. These heaters are typically located near the DEF reservoir.
If the PCM detects a voltage level on the reductant tank heater control circuit that is lower than the minimum allowable parameter, a code P202B will be stored and a malfunction indicator lamp (MIL) may illuminate. Multiple ignition cycles with a failure may be required for MIL illumination.
What is the severity of this DTC?
A stored code P202B 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 P202B trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P202B troubleshooting steps?
To diagnose a code P202B, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and access to vehicle-specific diagnostic information.
Consult your vehicle information source to find a technical service bulletin (TSB) that matches your vehicle’s year, make, model, engine size, stored codes, and exhibited symptoms. A relevant TSB may provide helpful diagnostic information.
Use the scanner connected to the vehicle diagnostic connector to retrieve all stored codes and relevant freeze frame data. It is recommended to 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 such cases, the underlying conditions may need to worsen before an accurate diagnosis can be made.
If the code is immediately reset, the next step in the diagnosis involves consulting 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 tank heater element according to the manufacturer’s specifications. Heaters are typically of the blanket or pin variety. Heater elements that do not test within the maximum allowable parameters should be considered defective.
Step 2
Use your vehicle diagnostic information source and the DVOM to test the reductant heater circuit voltage (usually battery voltage) with the system activated. If current conditions do not allow activation, use the scanner to manually activate the heater.
Step 3
If the reductant tank heater is functioning properly, use the DVOM to test the input and output signal circuits from the fuse panel, PCM, and ignition switch. Disconnect all controllers before using the DVOM for testing.
