Technical Description of OBD-II Trouble Code
The reductant injection valve for Bank 1 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 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 P20F6 indicates that the powertrain control module (PCM) has detected a stuck open reductant injection valve for engine bank 1 and selective catalyst reduction (SCR) system 1. Bank one refers to the bank of the engine that contains the #1 cylinder.
The catalyst system is responsible for reducing all exhaust emissions, although certain applications also have a NOx trap.
Exhaust gas recirculation (EGR) systems further reduce NOx. However, larger and more powerful diesel engines 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 precise timing of DEF injection enhances the performance of the filtration element, prolongs its longevity, and reduces harmful exhaust emissions.
The PCM or a stand-alone controller monitors and controls the entire SCR system. The controller uses input from O2, NOx, and exhaust temperature sensors to determine the appropriate time for DEF injection. Precise DEF injection is necessary to maintain acceptable exhaust temperature and optimize pollutant filtration.
Reductant heaters prevent diesel exhaust fluid from freezing in 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 P20F6 should be considered severe and addressed as quickly as possible. It could disable the SCR system and potentially cause catalyst damage if the underlying conditions are not rectified promptly.
What are some of the symptoms of the code?
Symptoms of a P20F6 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code include:
What are some P20F6 troubleshooting steps?
To diagnose a code P20F6, you will need 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, model, engine size, stored codes, and exhibited symptoms for additional diagnostic information.
Start 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 relevant 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 intermittent code may be more challenging at this time. It may be necessary for the conditions that contributed to the code being stored to worsen before an accurate diagnosis can be made.
If the code is reset, refer to the vehicle information source for diagnostic flow charts, connector pinout charts, connector face views, component testing procedures, and specifications. This information is essential for 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 power and ground circuits are within the appropriate range, use the scanner to activate the reductant injector valve (solenoid) and test the output control circuit voltage. Insufficient voltage may indicate a faulty or improperly programmed controller.
If the voltage output circuit meets specifications, use the DVOM to test the reductant injection valve in question. If the valve does not meet the manufacturer’s specifications, it may be faulty.
