Active Valve Control System AVCS (similar to Variable Valve Timing, VVT) allows the engine computer to advance or retard the camshaft for performance and emissions benefits. More info here.
Active Valve Lift System AVLS allows the engine computer to control the camshaft to use high lift lobes to allow more air into the engine as required. More info here.
For engine specific info find your engine in the section below. Most Subaru engines are candidates for head gasket failure even Subaru recommends adding the cooling system conditioner as an additive when replacing coolant although some say this was more to prolong engine life beyond the warranted period. It's basically a product to fill small tiny gaps also sold as Holts Radweld. A chemical block test can be performed where the special liquid changes colour in the presence of exhaust gasses but some people find that this generates false positives.
Common reasons for this generation head gasket failures include;
Aluminum engines do not like to overheat where the temperature gauge goes into the red zone. Common reasons for this generation Subaru to overheat include;
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Have a look at the factory service manual via the resource page for the full details, there's no point repeating that here. In a nutshell EJ engines are 4 cylinder, EZ's 6. 2: D-MFI-Non-turbo (SOHC). Common fuel feed systems are described as 3: MFI-Non-turbo (SOHC), 4: MFI-Non-turbo (DOHC), 5: MFI-Turbo, D: MFI-Non-turbo (DOHC, H6), F: MFI-Non-turbo (DOHC, LPG revision base), Z: CDI Turbo. Note that MFI here refers to multipoint fuel injection. A couple examples;
| Example 1 - EJ203 | Example 2 - EZ30D | |||
| Engine Type | E | 4 cylinder | E | 6 cylinder |
| J | Z | |||
| Displacement | 2 | 2 litre | 3 | 3 litre |
| 0 | 0 | |||
| Fuel Feed System | 3 | SOHC, non turbo | D | DOHC, non turbo |
On some models the fuel pressure regulator is in the tank, others under the hood. You can tell if there's 2 lines thru the firewall to the fuel system it's delivery & EVAP so the regulator is in the tank. If there's 3 its delivery, return & EVAP so you'll see the regulator under the hood.
If the engine is flooded the drive by wire (DBW) system will cut fuel if you hold the accelerator pedal 100% to the floor and then turn the key or push button to start the engine.
Check out the links for our pages with further information, enhancements, modification and tuning details.
| Code | Configuration | Notes |
|---|---|---|
| EJ203 | 2.0l single overhead cam | |
| EJ204 | 2.0l dual overhead cam | |
| EJ253 | 2.5l single overhead cam | |
| EJ254 | 2.5l dual overhead cam | |
| EZ30D | 3.0l dual overhead cam | Our EZ30 page |
It's not uncommon for Subaru catalytic converters to fail, typically with or without the P0420 code. The catalytic converter can fail in two ways, physically or chemically.
The honeycomb substrate inside the cat breaks down to clog to airflow, this appears as severe loss of power although low load and idling may seem ok. To test tap the catalytic converter with a rubber mallet ideally out of the vehicle to check for rattling.
Most all of this series vehicle have air fuel ratio sensors upstream of the cat(s) and oxygen sensors downstream. In steady state driving the engine computer manages fueling in a so called closed loop mode. The computer regularly switches the fuel mix very slightly rich and lean for optimum emissions efficiency. The front air fuel ratio sensor will see these variations but the rear oxygen sensor is expected to read rich (0.7+ volts) to demonstrate that the catalytic converter is storing oxygen for later use. If the rear oxygen sensor voltage alternates with the closed loop fuel variations the catalytic converter is not doing it's job. RomRaider can be used to log all of these parameters to diagnose the issue.
This failure doesn't generally affect driveability until the engine computer detects the problem and will raise a diagnostric trouble code and disable other functions such as cruise control. Note also P0420 can also be caused by bad electrical grounding to cause the sensors to work incorrectly.
P0420 Diagnosis thread at subaruoutback.org
Many parts of the exhaust are surrounded by thin metal heat shields, to protect the car from heat or enable components to warm up quickly. If these become rusty, bent or broken they can vibrate against the exhaust or car body to cause loud noises sometimes at certain speeds or engine temperatures.