Technical Description of OBD-II Trouble Code
Control Circuit/Open for Reductant Injection Air Pump
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Dodge, Ram, Sprinter, Mercedes Benz, Ford, Audi, Volkswagen, and others. While it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P2059 indicates that the powertrain control module (PCM) has detected an open circuit in the control circuit for the reductant injection air pump. The term “open” can be replaced with “disconnected.”
Modern larger and more powerful diesel engines that burn clean cannot meet the 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 developed.
The SCR system injects a reductant compound or diesel exhaust fluid (DEF) into the exhaust, along with a certain amount of air, in front of the diesel particulate filter, NOx trap, and/or the catalytic converter using the reductant injection valve (solenoid). The precisely timed DEF/air injection raises the temperature of the filtration element and allows it to function more efficiently. This enhances the longevity of the filtration element and reduces the release of harmful exhaust emissions 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. In either case, the controller monitors the O2, NOx, and exhaust temperature sensors (among other inputs) to determine the appropriate timing for DEF (reductant) and air injection. Precise DEF injection is necessary to maintain exhaust temperature within acceptable limits and optimize pollutant filtration.
The reductant/regeneration supply pump is used to pressurize the DEF in the liquid reductant system when needed. The PCM monitors the voltage of the supply pump to ensure consistent fluctuation and load percentage. The PCM also monitors one or more pressure sensors in the reductant supply system to detect any leaks in the system.
If the PCM detects an open circuit in the control circuit for the reductant injection air pump, a code P2059 will be stored and a malfunction indicator lamp (MIL) may illuminate. Multiple ignition cycles with a failure may be necessary for MIL illumination.
What is the severity of this DTC?
A stored code P2059 should be considered severe and addressed as soon as possible. It could disable the SCR system. Failure to rectify the conditions that led to the code being stored in a timely manner could result in catalyst damage.
What are some of the symptoms of the code?
Symptoms of a P2059 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P2059 troubleshooting steps?
Ensure that the reductant/regeneration supply system is not losing pressure, either internally or externally. Activate the pump to create pressure and inspect the system for external leaks. Use a fuel pressure tester to manually monitor reductant system pressure. Check the supply pump and injector for any leakage. If any leaks are found, whether internal or external, they must be repaired before proceeding with the diagnosis.
To diagnose a code P2059, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and access to vehicle-specific diagnostic information.
Consult your vehicle information source to find a technical service bulletin (TSB) that matches the year, make, and model of your vehicle, as well as the engine size, stored code/s, and exhibited symptoms. If you find a relevant TSB, it may provide helpful diagnostic information.
Use the scanner connected to the vehicle diagnostic connector to retrieve all stored codes and relevant freeze frame data. It is advisable to write down this information before clearing the codes, and then test-drive the vehicle until the PCM either enters readiness mode or the code is reset.
If the PCM enters readiness mode at this point, the code is intermittent and may be more challenging to diagnose. In such cases, 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 in your diagnosis will involve searching your vehicle information source for diagnostic flowcharts, connector pin-out charts, connector face views, and component testing procedures/specifications.
Step 1
Use the DVOM to test the control circuits, components, and sensors for the reductant injection air pump according to the manufacturer’s specifications. Circuit failure codes may be caused by faulty components or sensors. Sensors and components that do not test within the maximum allowable parameters should be considered defective.
Step 2
If the reductant air pressure is within specifications, the code P0259 persists, and all preliminary circuits, components, and sensors are functioning correctly, use the DVOM to test the input and output signal circuits between the sensors and the PCM/SCR controller. Disconnect all controllers before conducting the DVOM tests.
