P20CB Exhaust Aftertreatment Fuel Injector A Control Circuit/Open

Description and meaning of DTC p20cb

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 Mercedes Benz, Sprinter, GMC, Chevrolet, Ford, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration. If your diesel powered vehicle has stored a code P20CB, it means that the powertrain control module (PCM) has detected no voltage in the control circuit for the exhaust aftertreatment fuel injector, designated A. The designation A indicates that multiple reductant injectors are in use. The exhaust aftertreatment system (also called selective catalyst reduction system) is used to enhance the capabilities of the exhaust catalyst system. It may consist of one or more of these items diesel oxidation catalyst, diesel particulate filter, reductant injection system, ammonia slip catalyst, and a nitrogen oxide (NOx) trap. Among other things, exhaust aftertreatment systems (EAS) are responsible for the injection of reductant compound/diesel exhaust fluid (DEF) into the exhaust in front of the diesel particulate filter, NOx trap, and/or the catalytic converter via an automated fluid storage and injection system. Introducing DEF into the catalyst system promotes filtration element longevity and allows fewer harmful exhaust emissions to be released into the atmosphere. The EAS and catalyst systems are monitored and controlled by either the PCM or a stand-alone controller (which interacts with the PCM). The controller monitors the O2, NOx, and exhaust temperature sensors (as well as other inputs) to determine the appropriate time for DEF (reductant) injection. DEF injection must be performed at the appropriate instant and in precise measure in order to maintain an exhaust temperature that is within acceptable parameters and to optimize pollutant filtration. If the PCM detects no voltage on the control circuit for the EAS fuel injector, a code P20CB will be stored and a malfunction indicator lamp may be illuminated.

p20cb diagnostic trouble code symptoms

Symptoms of a P20CB trouble code may include:Diminished engine performanceExcessive black smoke from vehicle exhaustReduction in fuel efficiencyOther EAS/SCR related codes

DTC p20cb - possible causes

Causes for this code may include:Bad EAS fuel injectorOpen or shorted circuits in the EAS fuel injection control circuitInsufficient DEF in the EAS reservoirBad EAS controller/PCM or programming error

How to fix OBD-II diagnostic trouble code p20cb

A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P20CB. Locating 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, could yield helpful diagnostic information. I like to begin my diagnosis with a visual inspection of the EAS wiring harnesses and connectors. Burnt or damaged wiring and or connectors should be repaired or replaced before proceeding. I would continue by plugging the scanner into the vehicle diagnostic connector and retrieving all stored codes and pertinent freeze frame data. Consider writing this information down before clearing the codes. 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, completing the next step of your diagnosis will require that you search your vehicle information source to obtain diagnostic flow charts, connector pin-out charts, connector face views, as well as component testing procedures and specifications. You may also use your vehicle iformation source to pin-point the exact location of EAS fuel injector A. Use the DVOM to test (voltage drop) the power supply to the EAS control system. Test fuses with the circuit loaded to avoid misdiagnosis. If the appropriate power (battery voltage) and ground circuits are discovered, use the scanner to activate the EAS fuel injector (solenoid) and test output control circuit voltage. If voltage is insufficient, suspect that the controller is bad or has experienced a programming error. If the voltage output circuit is within parameters, use the DVOM to test the EAS fuel injector in question. If the injector fails to meet manufacturer’s specifications, suspect that it has failed. The EAS fuel injector is simply a solenoid based injector that sprays reductant fluid into the exhaustDon’t forget ground circuits when voltage drop testing

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