Technical Description of OBD-II Trouble Code
The reductant injection valve for engine bank 2 unit 1 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 vehicles from Ford, Mercedes Benz, Sprinter, Smart, Ram, etc. The exact repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P20F7 indicates that the powertrain control module (PCM) has detected a stuck open reductant injection valve for engine bank 2 and selective catalyst reduction (SCR) system 1. Bank two refers to the bank of the engine that does not contain the #1 cylinder.
The catalyst system is responsible for reducing all exhaust emissions, although certain applications are also equipped with a NOx trap.
Exhaust gas recirculation (EGR) systems go a step further in reducing NOx. However, larger and more powerful diesel engines today cannot meet strict federal (U.S.) emission standards with just the EGR, diesel particulate filter/catalytic converter, and NOx trap. This is why selective catalytic reduction (SCR) systems were invented.
SCR systems inject a reductant compound or diesel exhaust fluid (DEF) into the exhaust in front of the diesel particulate filter, NOx trap, and/or the catalytic converter via the reductant injection valve (solenoid). The precisely timed DEF injection increases the temperature of the filtration element, allowing it to perform more efficiently. This enhances filtration element longevity and reduces harmful exhaust emissions released into the atmosphere.
The entire SCR system is monitored and controlled by either the PCM or a stand-alone controller that interacts with the PCM. The controller monitors the O2, NOx, and exhaust temperature sensors, among other inputs, to determine the appropriate time for DEF (reductant) injection. Precise DEF injection is necessary to maintain exhaust temperature within acceptable parameters and optimize pollutant filtration.
Reductant heaters are used to prevent diesel exhaust fluid from freezing during extreme temperatures. These heaters are typically located in the DEF reservoir and/or the reductant injector supply hose/s.
What is the severity of this DTC?
A stored code P20F7 should be considered severe and addressed as quickly as possible. It could disable the SCR system and potentially cause catalyst damage if the conditions that led to the code being stored are not rectified promptly.
What are some of the symptoms of the code?
Symptoms of a P20F7 trouble code may include:
What are some of the common causes of the code?
Causes for this code may include:
What are some P20F7 troubleshooting steps?
To diagnose a code P20F7, you will need access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), and vehicle-specific diagnostic information.
If available, consult 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 helpful diagnostic information.
Begin the diagnosis with a visual inspection of the reductant heater system harnesses and connectors. Repair or replace any burnt or damaged wiring and connectors before proceeding.
Connect the scanner to the vehicle diagnostic connector and retrieve all stored codes and pertinent freeze frame data. Write down this information before clearing the codes and test driving the vehicle until the PCM either enters readiness mode or the code is reset.
If the PCM enters readiness mode, diagnosing the code may be more difficult at this time since it is intermittent. The conditions that led to the code being stored may need to worsen before an accurate diagnosis can be made.
If the code is reset, refer to the vehicle information source to obtain diagnostic flow charts, connector pinout charts, connector face views, component testing procedures, and specifications. This information is necessary to complete the next step of the diagnosis.
Use the DVOM to test the power supply to the SCR control system. Test fuses with the circuit loaded to avoid misdiagnosis. If the appropriate power (battery voltage) and ground circuits are present, use the scanner to activate the reductant injector valve (solenoid) and test the output control circuit voltage. Insufficient voltage may indicate a faulty or programmatically erroneous controller.
If the voltage output circuit is within parameters, use the DVOM to test the reductant injection valve in question. If the valve does not meet the manufacturer’s specifications, it may have failed.
