P20D8 Exhaust Aftertreatment Fuel Supply Control Circuit Performance

Description and meaning of DTC p20d8

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 VW, Audi, Mercedes Benz, Ford, Mitsubishi, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration. A stored a code P20D8 in your diesel powered vehicle means that the powertrain control module (PCM) has detected improper voltage that is outside the normal expected value range within the fuel supply control circuit for the exhaust aftertreatment system. 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. The reductant injection system is typically composed of at least one reductant injector, a reductant fuel storage tank, and high-pressure reductant fuel lines. A high-pressure, electronic pump is normally situated in the tank or in the fuel supply line. It is within the circuit which controls this supply pump that a malfunction has been perceived when a P20D8 is stored. 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. Precisely timed DEF injections elevate the temperature of the various filtration elements and allow them to perform more efficiently. 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 reductant fluid injection system pressure, O2, NOx, and exhaust temperature sensors (as well as other inputs) to determine the appropriate time for DEF (reductant) injection. If the PCM detects improper voltage that is outside the normal expected value range within the control circuit for the EAS fuel pump, a code P20D8 will be stored and a malfunction indicator lamp may be illuminated.

p20d8 diagnostic trouble code symptoms

Symptoms of a P20D8 trouble code may include:Diminished engine performanceExcessive black smoke from vehicle exhaustReduction in fuel efficiencyOther EAS/SCR related codes

DTC p20d8 - possible causes

Causes for this code may include:Bad EAS fuel supply pumpDefective EAS fuel pressure sensorOpen or shorted wiring in the EAS fuel supply control circuitInsufficient DEF in the EAS reservoirBad EAS controller/PCM or programming error

How to fix OBD-II diagnostic trouble code p20d8

A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P20D8. 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. Use the DVOM to test (voltage drop) on all EAS fuel supply system grounds. Continue by testing 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 pump and test output control circuit voltage. If voltage is insufficient, test the EAS fuel pump relay. If no input voltage is detected, suspect that the controller is bad or has experienced a programming error. If input voltage is present on the relay but output voltage is not detected, suspect that the relay is bad. If the EAS power supply voltage output circuit is within parameters, use the DVOM to test the EAS fuel pressure sensor and fuel pump. If any of these components fails to meet manufacturer’s specifications, suspect that it has failed. Don’t forget ground circuits when voltage drop testing

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