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The Mazda SkyActiv engine is very similar to other modern engines. It had an aluminum block and cylinder head, with a pair of chain-driven overhead cams. There are four pistons, 16 valves and one spark plug per cylinder – nothing out of the ordinary here.
However, the piston is dome-shaped like a performance piston to increase compression and has a small cup at the top similar to a diesel piston. The cups act like miniature combustion chambers and allow the flame front to spread rapidly as fuel is injected directly into these recessed cups at the top of each piston. The cup allows for faster burning and reduces the risk of explosion.
The engine also uses a continuously variable valve timing system to constantly vary the amount of valve overlap as well as intake and exhaust valve timing. This effectively reduces compression during the intake stroke, as well as the pumping loss that normally occurs when the throttle is nearly closed at idle and under light load.
The first SkyActiv applications started in 2013. Over the past seven years, this engine has made its way into nearly every platform and has even replaced some V6 engines. The machine is reliable, but there are four pattern failures you may see in your shop.
Engine or Accessory Mode Will Not Turn Off
There have been complaints from owners reporting that the engine will not turn off or the accessory mode cannot be turned off. The error is usually not in the advanced keyless entry module. Instead, it is data coming from other modules that prevents normal operation. The number one source of trouble is the transmission selector lever module. Source of problem number two is the brake pedal position sensor.
The shift lever and brake pedal inputs are used to determine the operation of the start button. Use a scan tool to verify the operation of the gear lever and brake pedal sensors. If the shifter reads a gear other than park, the button will not exit accessory mode.
If the car has a manual transmission, pay attention to the clutch pedal output.
P0101: Mass Air Flow Sensor
One of the most common fixes on the SkyActiv 2.5L was the mass air flow (MAF) sensor which caused P0101 to range A or P0171 mass airflow series because the system was too streamlined. The sensor may last only 60,000 miles. The main cause of the problem is sensor contamination. The sensor should produce 0.72 volts with the engine off. At idle with a warm engine, the voltage should be 0.86 volts. At 2000 rpm, the output should be 1.07 volts.
Misfire and Ice (Code P0300, P0301, P0302, P0303, P0304)
- Mazda3 2014-2018
- Mazda6 2014-2017
- 2016-2019 CX-3
- 2013-2019 CX-5
*With SkyActiv 2.0L and 2.5L
Machine
When the engine burns air and fuel in the correct proportions, only two by-products come out of the exhaust pipe namely CO2 and H2O. In TSB 01-007/19, Mazda details how water from combustion and condensation can build up in the exhaust system and freeze.
Frozen water can restrict the main damper of the exhaust system when the car is first started. The restriction causes random, specific cylinder misfire codes.
This can be an intermittent problem and depends on the weather. Also, if the shop is pulled to a warm shop, the problem goes away. Mazda has an updated main damper that allows water to flow.
Carbon Buildup
SkyActiv 2.0L and 2.5L engines can have problems with carbon deposits. The cause is usually oil and steam from the positive crankcase ventilation (PCV) system. This engine has a large oil separator under the intake manifold on the side of the block. The PCV valve is serviceable.
If excess steam passes through the PCV valve, carbon deposits on the inlet valve may occur. This vapor can fill with hydrocarbons and stick to the intake valves, causing carbon deposits problems.
One of the main causes of carbon deposits is owners using cheap conventional oil. Most conventional oils have a high volatility number, meaning they will evaporate more quickly when exposed to heat. A high number means the oil can get thicker over time and won’t lubricate as well. This also means that there is a larger volume of oil vapor in the PCV system that must be processed.
Synthetic oils have much lower volatility, reducing the amount of vapor and the possibility of carbon deposits forming on the intake valves, piston crowns or intake ports. Cylinder #4 will have the worst deposits and cylinder #1 will have the least buildup due to placement of the PCV hose.
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