P242F – Diesel particulate filter (DPF) – restriction/ash accumulation

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By Randy Worner (Contact Me)
Last Updated 2016-07-24
ASE/ACA World Class Technician
CodeFault LocationProbable Cause
P242F Diesel particulate filter (DPF) - restriction/ash accumulation
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Table of Contents

  1. What Does Code P242F Mean?
  2. What are the common causes of code P242F?
  3. What are the symptoms of code P242F?
  4. How do you troubleshoot code P242F?
  5. Codes Related to P242F
  6. Get Help with P242F

What Does Code P242F Mean?

The engine computer (PCM) monitors the amount of soot in the aftertreatment system, also known as the Diesel Particulate Filter (DPF). This system is more commonly thought of as a catalytic converter however, it actually traps small soot particles and holds them until they can be heated up, burned and turned into ash. This is the self-cleaning process that is part of the system controlled by the PCM. Under light load driving, the system may tell the driver to change driving characteristics in order to keep the DPF from becoming full of soot. If not, eventually the PCM will derate the engine (reduce power) until the soot in the DPF is reduced, thereby reducing exhaust backpressure.

The main inputs to the PCM for this system are the Exhaust Pressure Sensor and the Exhaust Temp Sensor, along with calculated soot output from the engine. This code tells us that the exhaust temperature coming out of the turbo charger is not high enough to support the burning off of the soot in the DPF. This burn off process is also known as regeneration.

Code P242F will set when the soot / ash levels in the aftertreatment diesel particulate filter system have went beyond the most severe possible.  Correction requires DPF replacement.

What are the common causes of code P242F?

  • Faulty Aftertreatment System / Diesel Particulate Filter – most common / plugged with ash and soot.
  • Root Cause – customers driving with light loads / not allowing exhaust to get hot enough.
  • Failed Exhaust Temperature Sensor(s) – Failed low – unlikely
  • Failed PCM – Very highly unlikely

What are the symptoms of code P242F?

  • Malfunction Indicator Light “ON”
  • Reduced Engine Power
  • Message Center / Instrument Cluster stating “Catalyst Full – Service Required”

How do you troubleshoot code P242F?

First, take a look and see if there are any technical service bulletins (TSB) for your particular vehicle. There may be an update, or known fix put out by the manufacturer that can save you from wasting time and money.

Next, see if there are any other diagnostic fault codes. Diagnose current faults first, in the order in which they are stored. Misdiagnosis occurs when this code is diagnosed when it is a stored code, especially while other codes are active. Also, check for active Exhaust Pressure Sensor and Exhaust Temp Sensor fault codes. If these codes are present, diagnose them before attempting to diagnose the P242F.

If the P242F is the only active fault code present, and there are no updates/TSBs for your particular vehicle, then the next step is to replace the Diesel Particulate Filter (DPF) and reset all the regenerative timers with a capable scan tool. The Exhaust Gas Recirculation (EGR) valve and its associated passages need to be cleaned as well. If your scan tool is unable to reset the regenerative timers, you will need to seek out a qualified, trained automotive diesel diagnostician. Before the DPF is to be replaced you should also make sure that:

  • There are no engine/fuel system problems. Anything that could cause the engine to run rough and generate more soot WILL cause the DPF to clog quickly and the more soot that enters the DPF, the more ash that eventually becomes trapped there. Once there is enough ash deposited inside the DPF, replacement is the only guaranteed solution.
  • Cleaning out the DPF is not possible. Some manufacturers have a process where the DPF is removed, and a high volume of pressurized air is forced in the opposite direction of normal exhaust flow. The contaminants are trapped in a hazardous waste container and the DPF is placed back into service after it is tested. This process only applies to those DPFs that can be serviced. If damaged, this also does not apply.
  • Only Ultra-Low Sulfur Diesel (ULSD) fuel is being used. ULSD cannot have more than 15 parts per million (PPM) sulfur. Most diesel fuels today have less than 5 PPM sulfur. Sulfur is one of the culprits that generates soot coming from the tailpipe of a diesel engine. When the manufacturer allows its use, B5 – B20 biodiesel can be used. B5 is 95% ULSD and 5% biodiesel. B20 is 80% ULSD and 20% biodiesel.
  • NO unapproved additives are being used in the fuel system. The additives we are talking about here include but are not limited to:
  1.   Large amounts of automatic transmission fluid (ATF). Phosphorus in the ATF causes problems for the DPF. Large amounts would be considered anything over one half gallon to a full tank (25 plus gallons) of diesel fuel.
  2.   The same holds true for used/waste motor oil. While certain manufacturers (Cummins being one of them) having a used oil system, where used motor oil is introduced into the fuel, mixed with it and then injected into the cylinder to be burned right along with the diesel fuel. These systems take only a small quantity of filtered engine oil from the crankcase at a time and replace it with fresh engine oil. These systems are engineered to mix the correct amount of oil with the correct amount of diesel fuel. Dumping used engine oil of unknown quality into the fuel tank of any vehicle is not going to end well. And we can’t forget;
  3.   Used /Waste vegetable oil / cooking oil. Does the oil stay liquid at room temperature? If not, it won’t stay that way in a diesel fuel tank either. What else is being dumped into the tank? Chicken parts? Breading? Enough said on this subject.


P242C & P242D Exhaust Gas Temperature Sensor(s) Circuit low – voltage on these circuits are low, which can cause the P242D to set as wellagain, unlikely both would set as well as the P242F

P244A Diesel Particulate Filter Differential Pressure Sensor Too Low – can set if the DPF is becoming restricted or has become completely clogged

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