P2458 – Diesel Particulate Filter Regeneration Duration

By Reinier (Contact Me)
Last Updated 2018-09-25
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P2458 Mean?
2. Where is the P2458 sensor located?
3. What are the common causes of code P2458?
4. Get Help with P2458

What Does Code P2458 Mean?

OBD II fault code P2458 is a generic code that is defined as “Diesel Particulate Filter Regeneration -Duration”, and is set when the PCM (Powertrain Control Module) detects that regeneration of the DPF (Diesel Particulate Filter) does not complete in the expected time frame. Note that this code only applies to diesel-powered applications.

The purpose of a DPF is to filter out and capture solid particles (soot) in diesel exhaust, and to hold on to the soot until a predefined soot load is reached, upon which the PCM initiates a process to burnt off the accumulated soot. This process is known “regeneration”, and if completed successfully, it restores the DPF’s ability to capture more soot until the next regeneration cycle occurs.

In practice, both a DPF’s ability to filter out soot, and its ability to regenerate successfully are critically important factors in emission control on diesel vehicles. However, may factors that include repeated short trips, excessive oil consumption and/or over fueling, can have serious negative effects on a DPF’s ability to regenerate, which can occur in one of three ways, these being-

Passive regeneration

This process relies on the temperature of the exhaust gas being high enough (typically, about 1100⁰F) to initiate and sustain the regeneration process. While this is often possible during sustained high-speed driving, the PCM may also adapt the fuel injection timing to create the required conditions. This mode of regeneration occurs automatically, and usually takes about 20 minutes or so to complete depending on the soot load, the application, and actual exhaust gas temperature.

It should be noted that the exhaust gas almost never reaches the required temperature when the vehicle is used for short trips in city-driving conditions, with the result that regeneration cannot take place. However, when such a vehicle is driven at high speed for a prolonged period, the DPF may be so clogged that regeneration may not burn off all the accumulated soot, or the process may take longer than expected.

Active regeneration

This process involves the injection of precisely measured doses of a liquid reductant, or a small quantity of raw fuel into the DPF when the exhaust gas temperature is high enough to initiate and sustain the regeneration process to completion. Failures of, or malfunction in the injection system can prevent the regeneration process from starting, completing successfully, or cause the process to take longer than expected.

Forced regeneration

In some cases, it may be possible to regenerate the DPF by using a scan tool to force the PCM to initiate the process, but how successful (or otherwise) the process is depends on both the accumulated soot load and the application.

It should be noted that the PCM uses various sensors that typically include exhaust gas temperature sensors and exhaust backpressure sensors to calculate the efficiency of the DPF as a function of the soot load in the DPF. Based on the minimum allowable efficiency (that varies somewhat between makes and models) of the DPF, the PCM will initiate a regeneration process automatically. However, if the PCM detects that the regeneration process does not complete in a predefined time period, it recognizes either that the DPF is defective, or that some undefined problems and issues exist that prevent the regeneration process from completing in the expected time period. In all cases though, the PCM recognizes that it cannot control the DPF regeneration process effectively, and it will set code P2458 and illuminate a warning light as a result. In some cases, the PCM may also initiate a fail-safe or limp mode that will persist until the fault is corrected, but note that if a fail-safe or limp mode is enforced, it may be impossible to start the engine (after switching it off) while the limp mode is in operation.

Where is the P2458 sensor located?

The image above shows the location of the DPF (circled) on a BMW application. Note however that since the actual appearance and location of DPF devices vary greatly between applications, it is important to refer to the manual for the affected application to locate and identify the DPF correctly. Be aware that many DPF devices can resemble mufflers and catalytic converters very closely, so be sure to identify the DPF correctly to avoid misdiagnoses and the unnecessary replacement of expensive, and perfectly usable exhaust system components.

What are the common causes of code P2458?

Some common causes of code P2458 could include the following-

• Defective DPF
• Defective exhaust gas temperature sensors and/or related wiring
• Defective exhaust backpressure sensors and/or related wiring
• Excessive oil consumption
• Over fuelling conditions as the result of leaking injectors or excessive fuel pressure
• Corrupted or defective software that affects injection timing and injector pulse widths
• Defective catalytic converter(s)
• Defective reductant injection system
• Failed or failing PCM, but note that this a rare event, and the fault must therefore be sought elsewhere before any control module is replaced

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