P202B Reductant Tank Heater Control Circuit Low

Description and meaning of DTC p202b

This diagnostic trouble code (DTC) is a generic powertrain code and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Volkswagen, Mercedes-Benz, Dodge, Audi, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration. A stored code P202B means 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 reduction of (basically) all exhaust emissions although certain applications are also equipped with a NOx trap. Exhaust gas recirculation (EGR) systems go another step further in the reduction of NOx. Nevertheless, today's larger and more powerful diesel engines cannot meet strict federal (U. S. ) emission standards with the EGR, diesel particulate filter/catalytic converter, and NOx trap alone. It was for this reason that selective catalytic reduction (SCR) systems were invented. SCR systems inject a reductant compound or a diesel exhaust fluid (DEF) into the exhaust in front of the diesel particulate filter, NOx trap, and/or the catalytic converter via the reductant injection valve (solenoid). The precisely timed DEF injection elevates the temperature of the filtration element and allows it to perform more efficiently. It enhances filtration element longevity and allows fewer harmful exhaust emissions to be released into the atmosphere. The entire SCR system is monitored and controlled by either the PCM or a stand-alone controller (which interacts with the PCM). Either way, the controller monitors the O2, NOx, and exhaust temperature sensors (as well as other inputs) to determine the appropriate time for DEF (reductant) injection. Precise DEF injection is necessary to maintain exhaust temperature within acceptable parameters and optimize pollutant filtration. Reductant tank heaters are used to prevent diesel exhaust fluid from freezing during extreme cold temperatures. These heaters are typically located in or around the DEF reservoir. If the PCM detects a level of voltage 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 be illuminated. Multiple ignition cycles - with a failure - may be required for MIL illumination.

p202b diagnostic trouble code symptoms

Symptoms of a P202B trouble code may include:Reduction in fuel efficiencyExcessive black smoke from vehicle exhaustDiminished engine performanceOther SCR related codes

DTC p202b - possible causes

Causes for this code may include:Bad reductant tank heater elementOpen or shorted circuits in the reductant tank heater controlBad SCR controller/PCM or programming error

How to fix OBD-II diagnostic trouble code p202b

A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P202B. You may use your source of vehicle information to locate a technical service bulletin (TSB) that matches the vehicle year, make, and model as well as the engine size, code/s stored, and symptoms exhibited. If you find one, it could yield helpful diagnostic information. Use the scanner (connected to the vehicle diagnostic connector) to retrieve all stored codes and pertinent freeze frame data. It is a good idea to write this information down before clearing the codes then test-drive the vehicle until the PCM either enters readiness mode or the code is reset. If the PCM enters readiness mode at this time, the code is intermittent and may be much more difficult to diagnose. If this is the case, the conditions which contributed to the code being stored may need to worsen before an accurate diagnosis can be made. If the code is immediately reset, the next step of your diagnosis will require that you search your vehicle information source for diagnostic flow-charts, connector pin-out charts, connector face views, and component testing procedures/specifications.

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