MY04 Legacy GT-B: air/fuel ratio sensor needs replacing again after 35,000km

[eddiewould]

Hey guys,

I had the air flow sensor air fuel ratio sensor replaced (CEL diagnosed by Armstrong) on my MY04 GT-B Leggy towards the end of 2010 - at a cost of $626 incl GST. This fixed the CEL then but it\'s started happening again. I\'ve had it diagnosed by Armstrong again and lo and behold, it\'s the same thing again.

The car is only done 35,000 kilometers in that time and has always been run on either 95 or 98.

How long should this part last? Is it possible/likely that they haven\'t found the root cause which is making this part fail? Anything else I should look out for? Or do I just have to stump up $600 every 3 years ???

NB the part is "SENSOR A/F RATIO 20Y - 20X"

Cheers,

Eddie

[KiwiJoe]

Get a can of MAF cleaner and give it a blast first. Less than $20 and definitely worth a shot. If that doesn\'t work maybe try a second hand one from a wrecker. They\'re super easy to replace yourself. I\'ve had some go and there doesn\'t seem to be a pattern, just luck of the draw. Do you have a standard air filter or an after market one?

[eddiewould]

Car is stock-standard (air filter replaced at 100k service, car now has ~120k on it)

Where do I get MAF cleaner from? If I go into Repco, will they know what I want? (Or do I need the Subaru upper engine stuff)?

Any idea what a second-hand one will go for (roughly)? Just trying to get an idea of whether it\'s worth the gamble.

Cheers for the reply!

[Rosssub]

AFR Air Fuel Ratio Sensor, I think KiwiJoe is referring to cleaning an AFM Air Flow Meter? Aftermarket oil type filters can clog AFM\'s

But I\'d do the same for your AFR Sensor, disconnect the battery (ECU reset) pull the sensor out and clean it with carb cleaner. Then refit and reconnect battery, might be good for another year?

MY04GTB has two AFR sensors doesn\'t it?

Edit: MAF and Carb cleaner\'s should be available by name at any auto store.

[Rosssub]

2 A/F Ratio Sensors would explain the $626 bill from Armstrong, maybe they\'ve replaced both in 2010.

It\'s the sensor bolted into your exhaust down pipe, just in front of the Cat. If you have 2 the second will be just after the Cat I think.

Edit: They should also be earthed near the sensor somewhere, might pay to check/clean the earths while under there?

[Marky]

Has the engine had any rebuild or service work done in recent history

I have heard of silicone sealants somehow contaminating 02 sensors to death, just from minute amounts of fumes being sniffed

Option b could be bad fuel, havent run a tank of waimak bp "special" fuel through it have ya? haha

Ahh memories

Just random ideas, its a weird part to die on its own. Theyre pretty "dumb" and generally do their simple job for 100-160ks before needing replacement

[eddiewould]

 Rosssub said:

2 A/F Ratio Sensors would explain the $626 bill from Armstrong, maybe they\'ve replaced both in 2010.

It\'s the sensor bolted into your exhaust down pipe, just in front of the Cat. If you have 2 the second will be just after the Cat I think.

Edit: They should also be earthed near the sensor somewhere, might pay to check/clean the earths while under there?

Pretty sure it was just one sensor they replaced last time. Some of that $626 was labour. I might have recently bottomed out my exhaust, I wonder if I could have damaged it somehow in the process? That would be a likely explanation.

[eddiewould]

 Marky said:

Has the engine had any rebuild or service work done in recent history

I have heard of silicone sealants somehow contaminating 02 sensors to death, just from minute amounts of fumes being sniffed

Option b could be bad fuel, havent run a tank of waimak bp "special" fuel through it have ya? haha

Ahh memories

Just random ideas, its a weird part to die on its own. Theyre pretty "dumb" and generally do their simple job for 100-160ks before needing replacement

No engine work in the 3.5 years I\'ve owned it. I could be imagining things, but I think it first started happening after filling up with BP Ultimate near Te Papa in Wellington. I normally just put 95 in.

[Rosssub]

Bottoming the exhaust shouldn\'t hurt the AFR sensor, it\'s tucked up the front. Probably just scrape your mid pipe.

I would consider 95 bad fuel, which could possibly kill your AFR premature? I only run 98 ever, I\'d reset my ECU after a tank of 95...But I\'m OCD lol

Edit: I cringe putting 95 in my lawnmower

[Marky]

When I say bad fuel I mean contaminated, not the octane level. That has 0 effect on the sensor

[Subirex Automotive]

95 octane wont affect your sensor, and as for cat being faulty, its out of the question. if your cat is faulty the code of p0420 will be logged and not p0031 or p0032, which is a/f ratio .

when you went to armstrongs, did they install the pak file(ecu reflash) for the a/f ratio sensor? subaru japan had released few ecu upgrade for these models where a/f ratio sensor gets buggered up too quickly.

go back to them and ask them if the pak file is available for your car. get that installed first before you change the sensor.

it happened to by bp5 as well, where the new sensor faulted only after 10,000km of driving. installed the file and it has been 2 years and hasnt faulted yet.

the reflash will not cost as much as the sensor. should be around an hour of labor plus the price of file that they have to acquire from subaru nz

[F.F.Sltd]

He has stated airflow sensor is he refering to the maf? And not the o2?

[Marky]

He did but the part description suggests otherwise

Im open to being wrong / subaru naming things backwards mind you

[eddiewould]

 Marky said:

He did but the part description suggests otherwise

Im open to being wrong / subaru naming things backwards mind you

Corrected topic - hopefully! My bad!

[eddiewould]

 subirex said:

when you went to armstrongs, did they install the pak file(ecu reflash) for the a/f ratio sensor? subaru japan had released few ecu upgrade for these models where a/f ratio sensor gets buggered up too quickly.

go back to them and ask them if the pak file is available for your car. get that installed first before you change the sensor.

I don\'t believe they installed any PAK files, no - or at least the invoice from them doesn\'t indicate that they did. The technician said (this time around) that the sensor has a high internal resistance so it\'s buggered - can\'t be cleaned or anything. I\'ve got the part on order with them, will ask them about PAK codes when the new one arrives.

Thanks for the help guys, and sorry for misleading everyone!

[Subirex Automotive]

if you can pm me your ecu number than i can check for the available pak file for your car

[slystiguy]

Probably a bit late to tell you know but you can get denso sensors on ebay for reasonable prices

[GorGasmSpecB]

Not sure why MAF cleaner would help a faulty O2 sensor...

[Rosssub]

 GorGasmSpecB said:

Not sure why MAF cleaner would help a faulty O2 sensor...

Carb cleaner, when they get caked in crud and can\'t read properly.

Edit: Never done it personally, but worth a shot at $250-$300 to replace? Would be the first thing I\'d try.

[drinkie9128]

My O2 (AFR) sensor went bad and I got an OEM one from rockauto.com for $160 NZD delivered. Winger were quoting $600!