P20D8 Exhaust Aftertreatment Fuel Supply Control Circuit Performance
OBD-II Trouble Code Technical Description
Exhaust Aftertreatment Fuel Supply Control Circuit Performance
What does that mean?
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.
What is the severity of this DTC?
A stored code P20D8 should be considered severe and addressed as quickly as possible. The EAS system may be damaged as a result of the conditions which contributed to the code P20D8 being stored.
What are some of the symptoms of the code?
Symptoms of a P20D8 trouble code may include:
Diminished engine performance Excessive black smoke from vehicle exhaust Reduction in fuel efficiency Other EAS/SCR related codesWhat are some of the common causes of the code?
Causes for this code may include:
Bad EAS fuel supply pump Defective EAS fuel pressure sensor Open or shorted wiring in the EAS fuel supply control circuit Insufficient DEF in the EAS reservoir Bad EAS controller/PCM or programming errorWhat are some P20D8 troubleshooting steps?
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 inspectio
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