This one arrived as a 2015 CX-3 1.5 SkyActiv with a list of complaints that looked unrelated: a chuffing noise from the engine, an oil pressure warning light, a burning smell and an oil leak. They are not unrelated. They are four symptoms of one fault, and the same pattern turns up on the 2.2 SkyActiv diesel.
The chain of events starts at the injector seals. They harden and go out of round, combustion gases start blowing past them, and that blow-by carries carbon down into the engine oil. The burning smell and the mess around the top of the engine come from the same leak path, through the seals that sit where each injector passes through the rocker cover.
The part that actually threatens the engine is what that carbon does further down. It ends up in the sump, and it packs solid into the oil pickup strainer. Once that strainer is blocked, the oil pump cannot draw what it needs however much oil is in the sump, and the oil pressure warning you are seeing is completely genuine.
Why an oil change does not fix it
The car in the video had already been to a main dealer, where it got an oil change and was sent on its way. Fresh oil does nothing for a blocked pickup strainer, because the blockage is a physical crust of carbon sitting between the oil and the pump. The warning light comes straight back, and every mile driven with genuinely low oil pressure is wearing the engine out.
What the Job Involves
DIY Car Service Guide
- Full service at home: oil, filters, plugs, fluids
- Which jobs are safe to DIY and which are not
- What a garage charges for each item, so you know the saving
Instant PDF download · works on phone, tablet or PC · 7-day money-back guarantee
How the Diagnosis Goes
Take the symptoms together, not separately
A chuffing or puffing noise, an oil pressure light, a burning smell and oil around the top of the engine are one fault wearing four hats on these engines. Treating them individually is how a car ends up having an oil change and coming back a fortnight later. If a SkyActiv has more than one of these, look straight at the injector seals.
Inspect the top of the engine around the injectors
With the cover off you can usually see the story written in carbon around the base of each injector. On this CX-3 the seal that sits on top of the rocker cover, where the injector passes through, was completely destroyed. The others were not as bad but were clearly on the way. That is the escape route for both the gases and the mess.
Expect all four sets of seals to need doing
There are two seals to think about per cylinder: the copper washer that seals the injector to the head, and the oil seal where the injector passes through the rocker cover. Both get replaced on all four cylinders. Doing only the worst one is a false economy, because the others are the same age and have lived the same life.
Be ready for a stuck injector
Carbon build-up can effectively glue an injector into the head. On this car they had to resort to special extraction tools and a slide hammer to get one out. This is the point where the job stops being DIY for most people, because forcing it wrong can damage the head and turn a large bill into a much larger one.
Drop the sump and look at the pickup
The sump comes off after a ring of 10mm bolts around the outer edge. Prise it carefully rather than levering hard on one spot, because a bent sump flange will not seal again. The oil pickup strainer inside is held by two 8mm bolts.
Confirm the strainer is blocked
On this engine the strainer was blocked solid from both ends. Not partly restricted, completely packed. Hold it up to the light: you should be able to see through the gauze. If you cannot, you have found why the oil pressure light is on, and you have found the thing that would have destroyed the engine if it had been left.
Clean it properly or replace it
The strainer either gets replaced or cleaned until it is genuinely clear, and clear means clear, not better than it was. A partially cleaned strainer puts you back in the workshop. While the sump is off, clean the sump itself out too, because carbon will have settled in the bottom of it.
Reassemble, refill and verify
New injector washers and rocker cover seals, sump back on with the mating faces properly cleaned and sealed, fresh oil to the correct Mazda specification and a new filter. Then a scanner to clear the stored codes, and a road test watching that the oil pressure warning stays away and the chuffing noise has gone. Only then is the job finished.
What the Fault Codes Look Like
The codes that turn up with this fault are typically oil pressure related, with P06DE and P055F being the ones seen on this car. They describe what the engine is measuring rather than what has caused it, which is why chasing the code on its own leads people to sensors and oil pumps.
Treat an oil pressure code on a SkyActiv as a reason to physically look at the injector seals and the sump, not as a reason to replace a pressure sensor. The sensor is usually telling the truth. That is the uncomfortable part of this fault: everything is working correctly and reporting a real problem.
Do Not Keep Driving It
This is one of the few faults where continuing to drive is genuinely likely to destroy the engine rather than merely make things worse. Low oil pressure means bearings are not getting the film of oil they rely on, and bearing damage is measured in minutes of running, not months of driving.
If the oil pressure light is on properly, the sensible move is to stop and get the car recovered rather than drive it to the garage. A recovery fee is a fraction of the cost of an engine, and it is a genuinely difficult thing to explain to an insurer afterwards.
Why This Happens on SkyActiv Engines
The combination that causes it is high injection pressures, a seal design that hardens with heat cycling, and an oil pickup strainer with a fine gauze that is very good at catching exactly the sort of carbon this fault produces. None of those is a defect on its own. Together they give a well-defined failure mode that appears at similar mileages across the range.
The practical lesson for owners is that the early signs matter. A faint chuffing noise or a slight smell of burning after a run is the point at which this is a seal job. Left long enough it becomes a seal job plus a sump job, and left longer than that it becomes an engine.
Common Mistakes
- Accepting an oil change as the fix. It changes nothing if the pickup strainer is blocked.
- Replacing the oil pressure sensor. On this fault the sensor is reporting reality.
- Doing the injector seals but not dropping the sump. The carbon that already went down there does not come back up.
- Cleaning the strainer only partly. Hold it up to the light. If you cannot see through it, it is not clean.
- Forcing a seized injector. Get the right extraction tools, or hand it to somebody who has them.
- Bending the sump while prising it off. A distorted flange will weep oil forever afterwards.
- Driving it while the pressure light is on. This is a recovery-truck fault, not a limp-home one.
