Subaru Exhaust Sensors, P0420, A/F, O2 etc.

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Subaru Exhaust Sensors, P0420, A/F, O2 etc.

Postby bigBADbenny » Mon Oct 05, 2020 1:52 pm

Exhaust sensors


Consider that the cel/dtc fault might be caused by the sensor, plug or loom being faulty or worn out, or from an issue upstream of the sensor, eg an inlet or exhaust leak, fuel supply, injector or spark issue.

For this reason it’s a good idea to note the cel code and lookup the diagnostics in your cars FSM workshop mannual, before firing the parts cannon.

Performing basic health checks on the car, including logging and learning view, long term fuel corrections (eg with a shop scanner), inlet and exhaust pressure testing for leaks, fuelling and ignition inspection and tests are essential for proper exhaust sensor operation.

FSM & parts faq:
viewtopic.php?f=6&t=34980

Download your year/market FSM, and search your CEL/DTC code and lookup the diagnostic info within the context/section of your particular engine, eg H4DO, H4SO, H4DOTC, H6DO being respectively: 4 cylinder dual cam, single cam, dual cam turbo, 6 cyl dual cam.


Its generally accepted that genuine oem exhaust sensors are the only viable option. Or see below for Denso equivalent parts.

Try a trusted local vendor, eg Bennys Custom Works (Australia)

The best price internationally for genuine oem items is usually Partsouq in UAE, or JapanParts, Amayama or other Japanese vendors online, but check your local options first.

If budget or availability is an issue try Denso equivalent part numbers from Cooldrive or Global EFI (Australian EFI specialists).
Best to contact their customer service before committing.

Its also possible to hack or fool the system in the case or persistent CELs, eg P0420.
Google the P0420 $5 fix, which involves drilling out a spark plug extender, installing it between the rear 02 sensor and exhaust.

Eg:
Mad Hornets cel eliminator:
https://www.walmart.com/ip/Mad-Hornets- ... /311489075
Or:
Universal M18x1.6 o2 Oxygen Sensor EXTENSION Spacer Stainless Steel
https://www.ebay.com.au/itm/30351157152 ... Track=true
Extenders are also commonly used to defeat the p0420 cel when using aftermarket headers, especially on untuneable n/a models:
viewtopic.php?f=15&t=36485#p448789

At your own risk and research of course.

Some people with fouled A/F and 02 sensors (running too rich) have had success cleaning the sensors with solvents, or burn off the soot with a torch. Once again at your own risk and research.

Denso exhaust sensor diagnostic FAQ, (thanks Cory)

https://densoautoparts.com/Portals/Dens ... MprHMtrV7w

If you suspect a damaged catalytic converter, its advisable to make a visual inspection using a probe camera, usually from the bung of the most adjacent exhaust sensor.
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