Fiat Fullback: Diagnosing and Fixing DPF & Oil Dilution Issues P252F

The Fiat Fullback is essentially a Mitsubishi L200 under the skin, sharing the same engine and many components. It carries the Fiat badge, but it’s hard to miss its Mitsubishi origins. This pickup blends familiar styling with reliable mechanicals, making it an interesting vehicle to work on.

Warning Lights on the Dashboard

The vehicle in question showed a flashing smoke emissions warning on the dashboard, but no check engine light was present. This kind of warning hints at issues related to exhaust emissions rather than a full engine malfunction. Recognising such alerts is important for a targeted diagnosis, especially in diesels where particulate filters play a big role.

Using the Launch X431 Euro Diagnostic Tool

To identify the problem, the Launch X431 Euro scanner was connected to the vehicle. Initially, the system identified the truck as a Fiat, but switching the software’s settings to Mitsubishi provided clearer fault descriptions. The scan quickly revealed error code P252F, signalling an issue requiring further investigation.

Understanding the Error Code: Engine Oil Level Too High

The code pointed to “engine oil level too high”, a common problem linked to oil dilution in these Mitsubishi engines. Oil dilution happens when unburnt fuel mixes with the engine oil, raising its level and contaminating the lubricant. On these models, the dipstick has an extra ‘X’ mark beyond the full line; this warns when oil dilution reaches a critical point, requiring urgent attention.

Checking Live Data: Oil and DPF Information

Further live data checks included oil level, Diesel Particulate Filter (DPF) differential pressure, temperature, and soot loading. Differential pressure across the DPF indicates how clogged the filter is. Readings around 10 to 15 millibars were noticed, about twice the normal level, suggesting the filter was dirty. Some technical data, however, was difficult to fully interpret, which is common with complex vehicle systems.

Oil Dilution and Frequent DPF Regenerations

Oil dilution often ties into frequent DPF regenerations. Regeneration is when trapped soot is burned off to clear the filter, but if this happens too often, it can cause fuel to seep into the oil. Monitoring average regeneration distance is useful but wasn’t clearly visible here. At 3,000 RPM, the engine showed around 100 millibars pressure, reinforcing the need for filter cleaning.

How to Clean the DPF

Cleaning the DPF involves flushing it with a special fluid to remove soot and contaminants. The process for this vehicle included:

1. Setting up the cleaning kit with the fluid and injection gun.
2. Identifying injection points on the pipe before the DPF.
3. Injecting the cleaning fluid with the engine off for 10 seconds, then letting it sit for 5 minutes.
4. Continuing to inject the remaining fluid while the engine runs to avoid backflow into the engine.
5. Being careful not to overfill to prevent fluid from entering the engine.

This approach helps restore the DPF’s function without costly replacements.

Completing the Cleaning and Reassembly

After fluid injection, the pipes were allowed to clear any condensation and foam before reconnecting the rubber hose and securing clips. White foaming exhaust was visible, confirming the chemical reaction inside the filter. This setup prepared the vehicle for the final cleaning phase with increased engine revs.

Post-Cleaning Engine Rev and Smoke Reduction

With the engine held at around 3,000 RPM for a few minutes, smoke output diminished significantly as the filter cleared. The DPF pressure dropped from near 100 millibars down to roughly 40, indicating the cleaning was effective.

Resetting Fault Codes and DPF Initialization

Clearing the fault codes alone didn’t fix the flashing warning. The diagnostic tool was then used for special functions to confirm the DPF exchange and reset the engine oil data. Once these steps were completed, the fault light stopped flashing. This method ensures the system recognises the DPF as clean and correctly logged.

Test Drive and Performance Notes

A 10 to 20 minute test drive confirmed the repairs. Interestingly, this Fiat Fullback felt more responsive in gear changes and power delivery compared to Mitsubishi L200 models id driven.

Advice on Oil Changes to Prevent Issues

To prevent oil dilution and DPF problems, keep oil change intervals to between 5,000 and 8,000 miles. Longer stretches, such as 15,000 miles, increase the risk of dilution and filter blockages. After each oil change, reset the oil with your diagnostic tool to keep readings accurate. Regular maintenance like this helps keep emissions systems healthy and avoids costly repairs.

Key tip: Frequent oil changes and proper resets greatly reduce oil dilution and DPF complications on these pickups.