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p0140 rear sensor no activity detected

Started by cameron, Feb 21 2014 10:34 AM

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#1 cameron

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Posted 21 February 2014 - 10:34 AM

Had this fault code come up twice this week very intermittent but seemed to be off throttle after giving it a bit of a boot and just coasting both times.

Basic diagnosis i have done is:

checking for voltage and its there and constant.

checked the sensor wiring for any defects and all seems good.

Sensor is filthy and the car does run a little rich so assuming sensor is gone.

 

Gave the local subaru dealer a call and $477 for a new one no thanks.

Already got a quote from subaru genuine parts and its $126us + post so ill be buying it from there.

 

Is there any benefit in doing the front one aswell. e.g both the same age and same KMs?


Have you put any more thought into squeezing some more power out of the engine. Like strapping on one of those intake fans

#2 allpaw4

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Posted 21 February 2014 - 11:20 AM

Front one is a wide band and is just under 1000 bucks from Subaru. If it isn't faulty, why replace it.

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#3 cameron

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Posted 21 February 2014 - 11:25 AM

assuming i have the correct part number

front is 22641AA211 its $146.36us from subaru genuine parts.

rear is 22690AA520 its $124.40 from subaru genuine parts or $477 from subaru aus


Have you put any more thought into squeezing some more power out of the engine. Like strapping on one of those intake fans

#4 allpaw4

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Posted 21 February 2014 - 01:32 PM

Wow, why not then. Cheap!

MY00 Red RX, a nice daily that was sold off once the B4 became reliable...
MY02 Blue B4, aka 'The Project' - v8 JDM STi engine package and assorted other 'goodies' - Sold, then bought back for parts. Stripped and crushed.
MY03 Blue RX, the newer old daily, pretty well more B4 than RX now... In the process of being converted to the track toy... Watch this space!
MY02 Silver Wagon, H6 conversion, full blue/black leather and almost full black interior to go with it.
MY03 White/Silver H6 Outback, donor car for silver waghoon.
MY97 Silver RX, acquired to become track car, but plans changed. To be stripped and scrapped in time.

#5 cameron

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Posted 01 March 2014 - 07:25 PM

so cel has been on for 2 weeks. reset ecu and code keeps coming back within 10 minutes so just left it on. tonight hit the limiter cells gone. drove another hour and cel hasnt come back :/ im confused

Have you put any more thought into squeezing some more power out of the engine. Like strapping on one of those intake fans

#6 RX25SE

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Posted 01 March 2014 - 08:53 PM

What model Subaru are we talking about?

 

The rear sensor is only used to monitor catalyst efficiency and it not used for fuel control.

 

You can test it with digital multimeter. It is a switching type sensor and would normally produce a cycling voltage between 0.1v and 0.9v when upstream of the cat. Downstream it would probably go from about 0.35v to about 0.55v.

 

 

When testing the rear sensor, give the throttle several decent sharp stabs to WOT to cause the overall mixture to go rich. This will use up the oxygen stored in the cat and cause the rear sensor to cycle over a greater voltage range (this might be why the code disappeared when you nailed it) as the catalyst efficiency has dropped off due to the rich mixture and no stored oxygen. If the engine has an air pump, this probably won't work.

 

 

My guess is a lazy/buggered sensor.

 

Out of curiosity, how many wires on the front O2 sensor?


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#7 Cam.

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Posted 01 March 2014 - 09:48 PM

Front O2 sensor is a 4 wire.


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#8 RX25SE

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Posted 02 March 2014 - 08:17 AM

That's what I would have thought.


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#9 cameron

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Posted 02 March 2014 - 02:15 PM

cars an 07xt lights back rear 02 sensor was ordered last week anyway so should be fixed this week

Have you put any more thought into squeezing some more power out of the engine. Like strapping on one of those intake fans

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