Technical Description of OBD-II Trouble Code
The fuel supply control for the exhaust aftertreatment system is stuck open.
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, etc. The exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If your diesel powered vehicle has a stored code P20DB, 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, enhances the capabilities of the exhaust catalyst system. It may include 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 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 that triggers a P20DB code occurs within the circuit that controls this supply pump.
Among other functions, the exhaust aftertreatment systems (EAS) inject reductant compound/diesel exhaust fluid (DEF) into the exhaust in front of the diesel particulate filter, NOx trap, and/or the catalytic converter. Precisely timed DEF injections increase the temperature of the filtration elements, allowing them to perform more efficiently. Introducing DEF into the catalyst system promotes filtration element longevity 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 injection.
If the PCM detects no voltage on the control circuit for the EAS fuel pump, it stores a code P20DB and may illuminate a malfunction indicator lamp.
What is the severity of this DTC?
A stored code P20DB 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 P20DB trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P20DB troubleshooting steps?
To diagnose a code P20DB, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and vehicle-specific diagnostic information.
Start by locating a technical service bulletin (TSB) that matches the vehicle’s year, make, and model, as well as the engine size, stored codes, and exhibited symptoms. This information can provide helpful diagnostic guidance.
Begin 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, the next step of the diagnosis requires searching the vehicle information source for 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 be the cause of the failure.
