Technical Description of OBD-II Trouble Code
Exhaust Aftertreatment Fuel Supply Control Circuit/Open
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from VW, Audi, Mercedes Benz, Ford, Mitsubishi, and others. While it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
If your diesel-powered vehicle has a stored code P20D7, it means that the powertrain control module (PCM) has detected no voltage in the fuel supply control circuit for the exhaust aftertreatment system.
The exhaust aftertreatment system, also known as the selective catalyst reduction system, is used to enhance the capabilities of the exhaust catalyst system. It may consist of components such as the diesel oxidation catalyst, diesel particulate filter, reductant injection system, ammonia slip catalyst, and a nitrogen oxide (NOx) trap.
The reductant injection system typically includes at least one reductant injector, a reductant fuel storage tank, and high-pressure reductant fuel lines. A high-pressure electronic pump is usually located in the tank or in the fuel supply line. The malfunction that triggers a P20D7 code occurs within the circuit that controls this supply pump.
Among other functions, exhaust aftertreatment systems (EAS) are responsible for injecting reductant compound/diesel exhaust fluid (DEF) into the exhaust system in front of the diesel particulate filter, NOx trap, and/or the catalytic converter. Precisely timed DEF injections raise the temperature of the various filtration elements, allowing them to operate more efficiently. Introducing DEF into the catalyst system promotes the longevity of filtration elements and reduces harmful exhaust emissions released into the atmosphere.
The EAS and catalyst systems are monitored and controlled by either the PCM or a stand-alone controller that interacts with the PCM. The controller monitors various sensors, including reductant fluid injection system pressure, O2, NOx, and exhaust temperature sensors, to determine the appropriate time for DEF (reductant) injection.
If the PCM detects no voltage on the control circuit for the EAS fuel pump, it will store a code P20D7 and may illuminate a malfunction indicator lamp.
What is the severity of this DTC?
A stored code P20D7 should be considered severe and addressed as quickly as possible. The EAS system may be damaged as a result of the conditions that led to the storage of the P20D7 code.
What are some of the symptoms of the code?
Symptoms of a P20D7 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P20D7 troubleshooting steps?
To diagnose a code P20D7, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and access to vehicle-specific diagnostic information.
It may be helpful to find a technical service bulletin (TSB) that matches the vehicle’s year, make, and model, as well as the engine size, stored code/s, and exhibited symptoms. This can provide valuable diagnostic information.
Start the diagnosis by visually inspecting the EAS wiring harnesses and connectors. Repair or replace any burnt or damaged wiring and connectors before proceeding.
Next, connect the scanner to the vehicle diagnostic connector and retrieve all stored codes and relevant freeze frame data. Consider writing down this information 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 point, the code is intermittent and may be more challenging to diagnose. In such cases, the conditions that led to the storage of the code may need to worsen before an accurate diagnosis can be made.
If the code is immediately reset, the next step of the diagnosis will require searching for vehicle information to obtain diagnostic flow charts, connector pin-out charts, connector face views, and component testing procedures and specifications.
Use the DVOM to test (voltage drop) all EAS fuel supply system grounds. Then, test 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 found, use the scanner to activate the EAS fuel pump and test the output control circuit voltage. If the voltage is insufficient, test the EAS fuel pump relay. If no input voltage is detected, suspect a faulty controller or a programming error. If input voltage is present on the relay but output voltage is not detected, suspect a faulty relay.
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 fail to meet the manufacturer’s specifications, suspect that they have failed.
