Ask the Mechanic: Why is my Rav4 diesel DPF full?

Hello Paul, I have a diesel 2013 Rav4.  Of  late, the message DPF full, see owner’s manual is always on display.  At some point, all dashboard lights started lighting and although a mechanic fixed this problem, it has resurfaced. What could be the problem and how can it be rectified? 


Hello Busingye, in full, DPF stands for Diesel Particulate Filter, which means your 2013 Rav4 is full of soot or particulate. Your diesel Rav4 has an engine management actuated regeneration system that should burn the ash accumulated in the DPF. That system seems not to be working. A computer diagnosis should tell a smart technician what has failed.

Some modern diesel engines in cars sold on European markets are fitted with emission pollutant trap devices called Diesel Particulate filters. These devices work with the engine management system via electrical, nitrogen oxide (nox) and oxygen sensors, temperature and pressure sensors which monitor the emission particulate or soot accumulation in the trap device. The engine management system will burn the ash or soot to regenerate the filter upon detection of the condition using the different sensors. The automatic regeneration of DPF may fail due to frequent short drives in slow traffic. Regeneration happens when the car is driven for about 20 minutes at speeds above 60kph.

Failure to achieve this condition may cause DPF trap device to accumulate too much soot. In this case, it has to be cleaned or replaced. On the other hand, the sensors the engine management system relies upon can fail, leading to failure to regenerate the DPF. Find a knowledgeable technician to establish why your DPF self-regeneration has failed.

A diagnostic check should be the first step. It is important to use the recommended low sulphur or low tar engine oil and diesel fuel.

Recommended fully synthetic engine oil will declare suitability to DPF. Low sulphur cleaner diesel fuel is also a crucial factor for DPF protection.


How do I know if my car’s timing belt needs changing?


A timing belt should be replaced before or at 100,000kms and after every 60,000kms thereafter, as recommended by most car manufacturers. Timing belts are ridged rubber belts that drive the engine camshafts and crankshaft in sync in order to ensure that each cylinder is fired at the correct time and sequence during combustion or burning of fuel.

This process is called engine timing. In the unfortunate event that an engine timing belt fails (slackens or snaps), the camshaft-driven valves and crankshaft-driven pistons will collide, causing extensive damage. Most of the newer, post 2000 engines have timing chains which have a longer lifespan and are less prone to failure as long as you use manufacturer recommended synthetic engine oils to service the engine.

The biggest challenge with following timing belt replacement schedules is car mileage fraud or tampering on some used cars. If you buy a used car whose mileage was reversed, you will most likely not know when the timing belt needs to be replaced. An aged timing belt can snap, causing severe damage or sag which retards or affects the engine timing, causing poor engine running and performance.

In the same vein, there are some car running symptoms that can suggest that you need to check the engine timing belt. The first is sudden engine stall and failure to start when you crank it persistently. Poor engine performance, characterised by hesitation, faltering or an engine rattle noise when driving uphill. This can be confirmed by a technician dismantling the engine to inspect the timing to see if it is aligned to the manufacturer recommended timing reference marks.

On some cars, a computer diagnostic check will confirm poor performance due to an ignition timing error which points to timing belt or timing chain aging which is causing retardation or poor timing.

Either way, always consult a mechanic before drawing a conclusion.

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