Honda Civic P24A4 PM Accumulation Quantity Excess

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Honda Civic P24A4 PM Accumulation Quantity Excess: Solving DPF and AC Issues

Blocked DPFs (Diesel Particulate Filters) are frustrating, but they're a common problem many drivers face. If you're grappling with error codes like "P24A4 - PM Accumulation Quantity Excess," you may be dealing with a blocked DPF on your Honda Civic. Let's go through the steps taken to address this issue and what caused it in this case.


What's Going On With This Honda Civic?

This Honda Civic arrived with DPF issues after a failed forced regeneration. The owner had driven 30-40 miles with the DPF light on but was unable to fix the problem elsewhere. The main issue? Too much soot in the DPF. This car’s DPF wouldn’t regenerate itself, and error codes indicated excessive particle matter accumulation.

On inspection, we also noticed other potential issues, such as low coolant levels and no gas in the car’s AC system. Both play a role in regeneration, so they needed attention.


Checking for Common DPF Blockage Causes

Blocked DPFs can arise from a few problems, so our first step was identifying the root. Here are some things we checked:

1. Oil Levels: Excessive oil can prevent regeneration. The oil level was slightly high, so some oil would need draining.
2. Air Conditioning (AC): The AC needs to engage properly for regeneration. Switching it on revealed a lack of pressure in the system, likely from a leak.
3. Differential Pressure: Measurement data showed 36g of soot and an 80 mbar pressure drop across the DPF, confirming it was clogged.

These findings pointed towards the AC system as a potential cause for the DPF blockage. Without proper AC function, the ECU prevents regeneration.


Fixing the AC System

Since the AC lacked any gas, we tested for leaks using a smoke detector tool. No visible leaks were found, so the system was refilled to restore pressure. However, after further testing, the AC pump showed signs of mechanical issues, even sparking at one point, despite intermittent engagement. While the system could now operate short-term, eventually, the AC pump will need a replacement.

This step was crucial because without a functional AC system, the car won't trigger regeneration cycles, leaving the DPF clogged over time.


Cleaning the DPF

Once the AC system was functional, we moved on to cleaning the blocked DPF. Here’s how the cleaning was done:

1. DPF Fluid Injection: A DPF cleaning solution was injected into the pressure hose at 120 PSI while the engine was running. This avoids backfilling into the cylinders.
2. Pressure Monitoring: Initially, pressure stood at 80 mbar. After the cleaning process, it dropped significantly to 24 mbar.
3. Revving the Engine: The engine was held steady at 2,500-3,000 RPM to eliminate remaining residue and dry out any residual fluid. The steam observed during this process was vapor, not harmful emissions.

With the cleaning complete, calculable particle matter dropped to just 0.3g, and the vehicle’s regeneration system was functional again.


Testing and Final Checks

After resolving the AC issues and DPF blockage, tests included clearing error codes and assessing whether the car could regenerate without manual intervention. Here's what was checked:

Engine Performance: Pressure readings stabilised at idle (0 mbar) and at higher revs (32 mbar, which is acceptable).
AC Engagement: The AC now engaged properly and allowed the car’s systems to trigger regeneration when required.

The error codes stayed cleared, and the auto-regeneration process was confirmed functional. A replacement AC pump is still recommended to ensure long-term reliability.


Conclusion

So, what caused the blocked DPF on this Honda Civic? The root of the issue was the non-functional AC system, which lacked gas pressure and prevented proper regeneration. After addressing the AC and performing a DPF clean, the car can now regenerate automatically.

If you're dealing with similar DPF problems, remember to check the basics like oil levels, AC functionality, and pressure readings. A small issue, like low AC gas, can spiral into a bigger, costlier problem if ignored. By addressing these underlying factors early, you can keep your car running smoothly and avoid the frustration of a blocked DPF.