Technical Description of OBD-II Trouble Code
The circuit controlling the fuel supply for the exhaust aftertreatment system is experiencing high voltage.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to many OBD-II vehicles (1996-newer), including VW, Audi, Mercedes Benz, Ford, Mitsubishi, and others. The specific repair steps may vary depending on the year, make, model, and powertrain configuration.
If your diesel powered vehicle has a stored code P20DA, it means that the powertrain control module (PCM) has detected excess 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 improve the performance of the exhaust catalyst system. It may include components such as a diesel oxidation catalyst, diesel particulate filter, reductant injection system, ammonia slip catalyst, and a nitrogen oxide (NOx) trap.
The reductant injection system typically consists of 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 fuel supply line. The malfunction detected by the stored P20DA code is within the circuit that controls this supply pump.
Among other functions, the exhaust aftertreatment systems (EAS) are responsible for injecting reductant compound/diesel exhaust fluid (DEF) into the exhaust system before the diesel particulate filter, NOx trap, and/or catalytic converter. Precisely timed DEF injections increase the temperature of the filtration elements, allowing them to operate more efficiently. Introducing DEF into the catalyst system promotes longevity of the filtration elements and reduces harmful exhaust emissions.
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, such as reductant fluid injection system pressure, O2, NOx, and exhaust temperature sensors, to determine the appropriate time for DEF (reductant) injection.
If the PCM detects excess voltage on the control circuit for the EAS fuel pump, it will store a code P20DA and may illuminate a malfunction indicator lamp.
What is the severity of this DTC?
A stored code P20DA 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 code being stored.
What are some of the symptoms of the code?
Symptoms of a P20DA trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P20DA troubleshooting steps?
To diagnose a code P20DA, 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 your vehicle’s year, make, and model, as well as the engine size, stored codes, and exhibited symptoms.
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, the code is intermittent and may be more difficult to diagnose. In this case, the conditions that led to the code being stored may need to worsen before an accurate diagnosis can be made.
If the code is immediately reset, you will need to consult your vehicle information source 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 power and ground circuits are functioning properly, 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 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, they may need to be replaced.
