Technical Description of OBD-II Trouble Code
The control circuit for the reductant tank heater is experiencing 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 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 P202C indicates that the powertrain control module (PCM) has detected excessive voltage in the control circuit for the reductant tank heater.
The catalyst system is responsible for reducing exhaust emissions, including NOx. Some applications also have a NOx trap.
Exhaust gas recirculation (EGR) systems further reduce NOx. 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 before the diesel particulate filter, NOx trap, and/or catalytic converter using the reductant injection valve (solenoid). The precise timing of DEF injection improves the performance of the filtration element, extends its lifespan, and reduces harmful exhaust emissions. The PCM or a stand-alone controller monitors and controls the entire SCR system, considering inputs from O2, NOx, and exhaust temperature sensors. Precise DEF injection is crucial for maintaining acceptable exhaust temperature and optimizing pollutant filtration.
Reductant tank heaters 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 exceeds the maximum allowable parameter, it stores a code P202C and may illuminate the malfunction indicator lamp (MIL). Multiple ignition cycles with a failure may be necessary for MIL illumination.
What is the severity of this DTC?
A stored code P202C should be considered severe and addressed promptly. It could disable the SCR system and potentially cause catalyst damage if the underlying conditions are not resolved in a timely manner.
What are some of the symptoms of the code?
Symptoms of a P202C trouble code may include:
What are some of the common causes of the code?
Possible causes for this code include:
What are some P202C troubleshooting steps?
To diagnose a code P202C, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and vehicle-specific diagnostic information.
Consult your vehicle information source to find a relevant technical service bulletin (TSB) that matches your vehicle’s year, make, model, engine size, stored codes, and symptoms. A TSB can provide valuable diagnostic information.
Use the scanner to retrieve all stored codes and 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 referring to 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 voltage (usually battery voltage) in the reductant heater circuit when the system is 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.
