Technical Description of OBD-II Trouble Code
Accumulation of Ash in the Diesel Particulate Filter Restricts Flow
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to most newer diesel vehicles (Ford, Mercedes Benz, Vauxhall, Mazda, Jeep, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
In rare cases, when a stored P242F code is detected, it means that the powertrain control module (PCM) has identified a level of ash restriction in the diesel particulate filter (DPF) that is considered to be restrictive. This code is only used in diesel-powered vehicles.
The DPF is a component that resembles a muffler or catalytic converter and is protected by a steel, inline exhaust housing. It is located before the catalytic converter and/or the NOx trap. The DPF element traps large soot particles while allowing small particles and other exhaust gas compounds to pass through.
The most crucial part of any DPF is the filtration element. The DPF can be made using various elemental compounds that trap soot while still allowing engine exhaust to pass through. These compounds include paper, metal fibers, ceramic fibers, silicone wall fibers, and cordierite wall fibers. Cordierite, a type of ceramic-based filtration compound, is the most commonly used fiber in DPF applications. It is inexpensive to manufacture and has exceptional filtration characteristics.
As exhaust flows through the element, large soot particles are trapped between the fibers. When enough soot accumulates, the exhaust pressure increases and the filtration element must be regenerated to allow spent exhaust gases to continue flowing through.
Ash accumulation is a side effect of DPF filtration and regeneration. It is caused by the prolonged use of incombustible materials such as lubricant additives, trace elements in diesel fuel/additives, and debris from engine wear and corrosion. Ash typically accumulates along the DPF walls or in plugs near the rear of the filtration element. This significantly reduces the effectiveness of the filtration element and decreases the filter’s capacity to store soot.
Because the ash is located near the walls and rear of the DPF, soot particles are pushed to the front, resulting in a reduction in channel diameter and filter length. This can lead to increased flow velocity through the DPF and an increase in the output signal voltage of the DPF pressure sensor.
When the PCM detects significant variations in DPF flow, velocity, or volume, a code P242F is stored and a malfunction indicator lamp (MIL) may illuminate.
Severity & Symptoms
The conditions that cause the code P242F to be stored can potentially cause internal engine or fuel system damage and should be addressed promptly.
Symptoms of a P242F code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known problem with a known solution provided by the manufacturer, which can save you time and money during diagnosis.
When diagnosing a code P242F, you will need a diagnostic scanner, a digital volt/ohmmeter, and a reliable source of vehicle information (such as All Data DIY). Begin by visually inspecting related harnesses and connectors, focusing on wiring near hot exhaust components and sharp edges (such as exhaust shields). Connect the scanner to the vehicle diagnostic connector and retrieve all stored codes and freeze frame data. Record this information for future reference, as it may be helpful if the code is intermittent. Next, clear the codes and test-drive the vehicle.
If the vehicle has been using excessive engine additives and fuel system additives, or if the DPF regeneration schedule has been ignored (in the case of passive DPF regeneration systems), it is likely that ash accumulation is the cause of the stored code. Most manufacturers of modern clean diesel fuel-powered vehicles recommend a maintenance schedule for DPF ash removal. If the vehicle is approaching or has reached the mileage requirement for DPF ash removal, ash accumulation is likely the problem. Consult your vehicle information source for DPF ash removal procedures.
If the code immediately reappears, consult your vehicle information source for instructions on testing the DPF pressure sensor using a digital volt/ohmmeter. If the sensor does not meet the manufacturer’s resistance specifications, it should be replaced.
If the sensor is functioning properly and the supply hoses for the DPF pressure sensor are not clogged or broken, begin testing the system circuits. Disconnect all related control modules before testing circuit resistance and/or continuity with the digital volt/ohmmeter. Repair or replace any open or shorted circuits as necessary.
Additional diagnostic notes:
