Common faults below

Subaru Engine Carbon Cleaning

What we see most on Subaru engines, what causes it, and which clean fixes it. Every job starts with a scan and a quote at our Kings Park workshop.

Free scanbefore any work
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Which Subaru do you have?

Subaru splits into three quite different groups, and which one you own decides everything below.

If you have the 2.0-litre boxer diesel — the EE20, sold here in the Outback, Forester and Legacy from around 2008 to 2014 — you have the world’s first production boxer diesel for passenger cars. They are good engines driven the right way, and difficult ones driven the wrong way. Short trips, and the habit of holding a high gear at low revs, are what kill them: the engine and filter never get hot enough to clear their own soot.

If you have a petrol boxer, whether it needs anything depends on which engine it is. Some use direct injection alone and build deposits on the intake valves; others also have port injectors that wash the valves and largely prevent it. We check before recommending the job.

And if you have an e-Boxer, the petrol engine runs gently and rarely gets hot, which brings its own kind of build-up.

Common Subaru carbon problems

What we see

If you drive a petrol Subaru

Petrol

Intake Valve Carbon on the Petrol Boxer

The direct-injection boxer engines put fuel into the cylinder, so nothing washes the back of the intake valves.
Oil vapour from the breather bakes onto the hot valve and forms a crust that narrows the port.
Which engine you have matters — some Subaru petrol engines also use port injectors that spray the valves, which largely prevents this.

Lumpy idle, worst when cold.
Hesitation off the line and a soft mid-range.
Misfire codes (P0300–P0304) with no ignition fault found.

Walnut blasting is the fix on the engines that need it — the intake comes off and each port is cleaned mechanically.
We check your engine before quoting. If yours has port injectors washing the valves, we will tell you it does not need doing.

Fixed by

Walnut Blasting

Quoted after the free scan

See the service →

If you drive a diesel Subaru

Diesel

Particulate Filter and Turbo Vanes on the EE20 Diesel

A regeneration needs the exhaust hot, and it only gets hot if the engine is worked. Driving in too high a gear at too low an rpm is the classic way to starve it.
Soot that cannot be burnt out of the filter also settles on the variable vanes of the turbocharger, where it gums up the mechanism.
Once the vanes bind, the actuator can no longer sweep them properly and the car stores boost pressure faults and drops into limp mode.

DPF light, then limp mode.
Boost pressure fault codes as well as filter codes.
A car that has become noticeably gutless before any light appeared.
Regeneration cycles happening more and more often.

Where we can, we clean the filter on the car — nothing removed, cut open or replaced. If it has to come off, it gets a three-stage clean and new gaskets, quoted first.
We look at what loaded it, because a filter cleaned on a car that is still driven the same way will simply block again.
Driving it in a lower gear and letting it rev is genuinely part of the fix on this engine — we will tell you that rather than let you find out the expensive way.

Fixed by

DPF Cleaning

From $715

See the service →

Diesel

EGR and Intake Soot on the Diesel

The EGR valve routes sooty exhaust gas into the intake, where it meets oil mist from the crankcase breather.
The mixture leaves a thick, greasy film that narrows the intake runners.
On a car that has spent years doing short trips this has had a long time to build.

A throttle that feels dead until the revs come up.
A sootier exhaust tip than the car used to leave.
An idle that will not settle, with EGR flow codes stored (P0401, P0402).

We clean the EGR circuit and the intake manifold so the airway is clear again.
On an EE20 this is worth doing alongside the filter rather than on its own — they load each other.

Fixed by

EGR & Intake Manifold Cleaning

Quoted after the free scan

See the service →

Diesel

Injector Fouling on the Diesel

Deposits on the injector tips spoil the spray pattern, so diesel arrives as droplets rather than a fine mist.
Poor combustion makes more soot, which loads the filter and the turbo vanes faster.
These cars are old enough now that the injectors have had a long time to accumulate deposits.

Hard starting from cold.
A rattly, uneven idle.
Smoke on start-up and worse economy.
Fuel rail pressure codes (P0087, P0088, P008A).

We clean the whole fuel system on the car with the engine running — injectors, pump and rail — nothing removed or sent away.
On a car this age it is often the cheapest thing that meaningfully changes how it drives.

Fixed by

Diesel Injector Cleaning

Quoted after the free scan

See the service →

If you drive a hybrid Subaru

Hybrid

The e-Boxer Hybrids

In an e-Boxer the petrol engine is assisted at low speed and switched off more often, so it works less hard than the engine it is based on.
It rarely reaches the temperature that keeps a combustion chamber clean.
Soft carbon accumulates at kilometre readings that look far too low to explain it.

Roughness as the engine cuts in and out.
The engine sounding busier than the speed suggests.
A car that feels less crisp than when it was new, with nothing stored.

A hydrogen carbon clean suits this — nothing comes apart, and it works on soft carbon before it hardens.
On a hybrid this is prevention, not repair.

Fixed by

Hydrogen Carbon Clean

$275

See the service →

Applies to any Subaru

Any Subaru

Short Trips and Cold Starts

A Subaru doing short suburban runs never gets properly warm, and a boxer engine takes a while to get there.
The intake side, the fuel side and the exhaust side all get dirty together on that duty cycle.
Fixing one and leaving the rest is why the same complaint keeps coming back.

A car that feels flat and heavy compared with how it drove when newer.
Idle that differs from one cold morning to the next.
Several unrelated-looking faults over a short period.

A boxer that has spent its life cold needs both sides done rather than one — a full engine carbon clean covers the pair in a single visit.
We scan first and give you a price before any work begins.

Fixed by

Full Engine Carbon Clean

From $715

See the service →

Keeping your Subaru clean

Prevention

To keep an EE20 diesel Outback, Forester or Legacy clean, work it hard enough to get the engine and filter hot. Nas’s rule of thumb is a steady run of about half an hour every week, or an hour every fortnight. Short trips and lazy, low-rev driving leave the soot behind. Direct-injection petrol boxers can build carbon on the intake valves instead. The e-Boxer runs gently and rarely gets hot, so a hydrogen carbon clean is prevention, not repair.

If your Subaru shows a DPF warning light or drops into limp mode, book a time at our Kings Park workshop. We scan it free first, tell you what it needs, and quote before any work starts. On the EE20, that may be an on-car DPF clean with an EGR and intake clean alongside, because the two load each other. On a petrol boxer that needs it, it may be walnut blasting.

Thank you so much! The shop owner was very proactive in helping me solve my problem and provided excellent maintenance advice. His craftsmanship is outstanding. He recommended the right cleaning products, which saved me money. I will definitely recommend this place to my friends! The prices are reasonable. Thank you boss.

Yuhao Yang, Subaru Forester 2.5i-S · Google review

Before any engine work on your Subaru, search your VIN on the government vehicle recalls site. Recall repairs are free, so check there first.

Drop a gear and let the diesel rev. Holding a high gear at low revs starves the self-clean (DPF burn) of heat. On the EE20, how you drive it is part of the fix.
Book it in when it goes gutless, not when the light comes on. On the EE20, lost pull can show before any light. The same soot settles on the turbo vanes, and once they bind the car drops into limp mode.
Have the injectors cleaned on an ageing EE20. These cars have had a long time to collect deposits on the injector tips. A poor spray makes more soot, which loads the filter and the turbo vanes faster.
Give a boxer more than a quick suburban run. A boxer engine takes a while to get properly warm. On short runs, the intake, fuel and exhaust sides all get dirty together.

Book your Subaru in

Get a free quote

Tell us the model, the kilometres and what it is doing. We will scan it and tell you which clean it needs, and what it costs, before any work starts.

Get a Free Quote Call Nas — 0455 455 644