Smell fumes inside the car?
Exhaust gas in the cabin can make you sick. Open the windows, pull over somewhere safe, switch off and get out if you feel dizzy or unwell, and don't drive it until it's been checked. If there's smoke or a burning smell, stop and switch off. If anyone is hurt or in danger, call 000.
What does a DPF do, and why does it block?
A DPF sits in a diesel's exhaust and traps soot. It can't hold soot forever, so the car burns it off, which is called regeneration. RACQ says that happens by itself on sustained highway driving, and you're unlikely to notice.
When soot builds up in town, the engine computer steps in. It adds a little extra fuel to lift the filter to around 600 degrees C. RACQ says that typically needs five to 25 minutes at about 80 km/h or more, usually with dash lights flashing.
Low-speed, stop-start driving can stop that starting or finishing, and RACQ says it's the most common cause of DPF problems. RAA's fix for a car that does mostly short trips is a weekly 20 to 30-minute drive at highway speeds.
DPF light on? What to do
Read the manual's DPF page
RACV says to follow the maker's instructions. Most want a run at a set speed and distance, and the manual gives the details for your car.
Don't switch off mid-way
If the regeneration has started, let it finish. RACQ says it has to run its course.
Look for other lights
RACV says if the check engine light is on as well, another fault may be stopping the filter clearing. That's one for a mechanic.
Act before limp mode
Ignored, RACQ says the car loses power and may go into limp-home mode. Then it needs a forced regeneration with a scan tool, and possibly an oil and filter change because fuel has got into the oil.
What is DPF cleaning?
The word gets used for a few different jobs. The first is a forced regeneration, where a scan tool tells the car to burn the soot off. The second is taking the filter off for cleaning. The third, when neither will do it, is a new filter, and RACQ calls that very expensive.
Ask which one you're being offered, and what the mechanic did to find the cause. A blocked filter is often a symptom. If a fault or the way the car gets driven caused it, it'll block again.
If yours keeps blocking even with regular long runs, tell the mechanic, because that points to a fault rather than the driving. Some diesels have a known DPF history, so ask the mechanic or the maker to check the VIN for any program or recall that applies.
Can I just remove the DPF?
We wouldn't, and we'd be wary of anyone who offers. Queensland's vehicle standards regulation makes it an offence to drive a light vehicle with an exhaust modified in a way that reduces its effectiveness, and it gives removing the DPF or a silencing device as examples. The maximum penalty is 20 penalty units.
EPA Victoria says it's against the law to use a vehicle that doesn't meet emissions standards, and that it can't approve changes such as DPFs. Rules differ between states, so check yours before anyone touches it.
Exhaust noise, leaks and catalytic converters
A blowing exhaust usually starts as a rust hole, a split flex pipe or a failed gasket. You'll hear it first on a cold start. Pipes and hangers can often be repaired, while a rusted-through muffler usually gets replaced.
Noise has limits. In NSW, the EPA sets a maximum stationary level of 90 decibels for a car built after 1982 and 96 for older ones. It also bans temporary fixes like steel wool in the muffler. If you get a vehicle inspection notice, you or a mechanic of your choice can do the repairs.
A catalytic converter is a different case. RACQ says misfires, rich mixtures, burnt oil and speed bump hits are what kill them, so fix the cause first or the new one goes the same way.
What a good written exhaust or DPF estimate shows
- Which section is leaking, and repair or replace.
- Clamps, hangers and gaskets, if they're needed.
- For a DPF: the fault codes, and the soot reading if the scan tool shows one.
- What method is being used, and what caused the blockage.
- An oil and filter change, if fuel has got into the oil.
- What the car should do afterwards to keep it clear.
What you can do, and what to leave
You can
- Take the highway run your manual describes when the DPF light asks for it.
- Mix some longer drives into a short-trip week.
- Listen to a cold start, and note where the noise comes from.
- Take a photo of the dash lights.
Leave to the mechanic
- Anything under the car. The exhaust stays hot well after you park.
- Forced regeneration and scan tool work.
- Welding, cutting and fitting.
- Catalytic converters and sensors.
Where we'd start
For a rattle or a loud exhaust, any good mechanic with a hoist can look at it, and it's usually a straightforward quote. For a DPF, we'd go to someone who works on diesels every week, and we'd ask what caused it before we'd pay to clear it. If the car only does short trips, it's worth an honest chat about whether that will change. Send us the car and the light you're seeing, and the mechanic can start from there.