Technical Description of OBD-II Trouble Code
The reductant injection valve circuit for Bank 2 Unit 1 is experiencing low 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 Ford, Mercedes Benz, Sprinter, Smart, Ram, and others. The exact repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P2051 indicates that the powertrain control module (PCM) has detected insufficient voltage in the control circuit for the reductant injection valve for engine bank two and selective catalyst reduction (SCR) system one. Bank 2 refers to the bank of the engine that does not contain the number one cylinder.
The catalyst system is responsible for reducing all exhaust emissions, although some 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 using the reductant injection valve (solenoid). The precise timing of DEF injection increases the temperature of the filtration element, allowing it to perform more efficiently. This improves 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 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 in extreme temperatures. These heaters are typically located in the DEF reservoir and/or the reductant injector supply hose(s).
If the PCM detects insufficient voltage on the control circuit for the reductant injection valve for engine bank two unit one, a code P2051 will be stored and a malfunction indicator lamp may illuminate.
What is the severity of this DTC?
A stored code P2051 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 P2051 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P2051 troubleshooting steps?
To diagnose a code P2051, 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, and model, as well as the engine size, stored codes, and exhibited symptoms. This can provide helpful 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 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. The conditions contributing to the stored code may need to worsen for an accurate diagnosis.
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 necessary 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 correct, 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 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 be defective.
