Technical Description of OBD-II Trouble Code
The circuit controlling the exhaust gas recirculation cooling valve 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 VW, Nissan, Audi, Ford, and others. The specific repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P2426 indicates that the powertrain control module (PCM) has detected insufficient voltage on the exhaust gas recirculation (EGR) cooling valve control circuit. EGR cooling systems are only used in diesel engine applications.
The EGR system is designed to redirect a portion of inert exhaust gases back to the engine induction system, replacing oxygen-rich clean air. This substitution reduces nitrogen oxide (NOx) particles, which are regulated by federal mandate due to their contribution to ozone-depleting exhaust emissions.
EGR cooling systems are used to lower the temperature of EGR gases before they enter the engine air induction system. The EGR cooling system functions similarly to a radiator or heater core, with engine coolant flowing through a finned area where EGR gases pass. A cooling fan may also be used. The electronically controlled EGR cooling valve regulates the flow of engine coolant to the EGR cooler under specific conditions.
The PCM uses input signals from the engine coolant temperature (ECT) sensor and the EGR cooler temperature sensor(s) to determine when and to what extent the EGR cooling valve should be opened or closed. The PCM monitors the voltage of the EGR cooling valve control system whenever the key is turned on.
The ECT and EGR cooler temperature sensors provide the PCM with information about variations in EGR cooler and engine coolant temperature. The PCM compares these input signals to determine if the EGR cooling system is functioning as intended. EGR temperature sensors are typically located near the EGR valve, while ECT sensors are usually positioned in a cylinder head water jacket or intake manifold water jacket.
If the voltage of the EGR cooling valve control system is too low, below the normal range of programmed parameters, or if the input signals from the EGR temperature sensor(s) do not match those of the ECT sensor, a P2426 code will be stored and a malfunction indicator lamp may illuminate.
The EGR valve is one component of the EGR system:
What is the severity of this DTC?
A stored code P2426 is related to the exhaust gas recirculation system and should not be considered severe.
What are some of the symptoms of the code?
Symptoms of a P2426 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P2426 troubleshooting steps?
Before proceeding with a diagnosis of the stored P2426, ensure that the engine cooling system is filled to the proper level with the appropriate coolant. If there are any engine coolant leaks or if the engine is overheating, these issues must be addressed first.
To diagnose a P2426, you will need a diagnostic scanner, a digital volt/ohmmeter, a source of vehicle information, and an infrared thermometer (with a laser pointer).
Start by visually inspecting the wiring harnesses and connectors associated with the EGR temperature sensor and the ECT sensor. Pay close attention to harnesses that are near hot exhaust pipes and manifolds.
Connect the scanner to the vehicle diagnostic port and retrieve all stored codes and relevant freeze frame data. Before clearing the codes and test driving the vehicle, it is recommended to write down this information in case the code proves to be intermittent.
At this point, one of two things will happen: either the PCM will enter readiness mode (with no codes stored) or the P2426 code will be reset.
If the PCM enters readiness mode, the P2426 code is intermittent and will be more challenging to diagnose. In many cases, the condition will need to worsen before an accurate diagnosis can be made.
If the P2426 code is reset, use the scanner data stream to monitor EGR temperature sensor data and ECT sensor data. Narrowing the scanner data stream to include only relevant information will provide faster data response. If the scanner indicates that EGR temperature and ECT are within acceptable parameters, suspect a defective PCM or a PCM programming error. However, this is the least likely scenario.
If the EGR temperature sensor data or ECT sensor data is erratic or not within the desired parameters, test the sensor(s) in question by following the testing procedures and specifications provided in your source of vehicle information. Sensors that do not meet the manufacturer’s specifications should be considered defective.
Use the DVOM to test the EGR cooling valve control circuit if the sensors are working properly. Remember to disconnect all related controllers before testing. Repair or replace any open or shorted circuits as necessary.
If all EGR cooling valve control sensor circuits are intact, use the infrared thermometer to measure the exhaust gas temperature at the EGR cooler (valve) inlet and outlet while the engine is running at normal operating temperature. Compare your findings with the manufacturer’s specifications and replace any faulty EGR cooling system components as needed.
