O2 Sensor
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Joined: Jul 2006
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O2 Sensor
I posted this thread a few days ago, but got no reponses. Any suggestions would help!
Malfunction Indicator Lamp (MIL) came in a few days ago, and I realized a definite decrease in MPG and engine performance.
I had Autozone run the OBDII test on my A6 2.8 and the diagnostic gave me the following result.
<Troubleshooting P0056>
HO2S22 Heater control circuit
explanation: open or short circuit condition
probable cause: 1) poor electrical connection, 2) failed HO2S
message: 'PCM has determined that a malfunction exists in the heater control circuit for O2 sensor 2 in bank'
I read the tech article 'diagnosing O2 sensor heater code', but my error code (P0056) doesn't seem to be in the code table. But googling shows that P0056 represents 'DTC P0056 HO2S Heater Circuit Bank 2 Sensor 2'
So, am I certain that B2 S2 sensor IS the problem? Could the problem be coming from elsewhere?
a_o_smith's 'O2 sensor replacement' posting shows good picture of the location of the sensors and the plugs, but is there any tech article on replacing the O2 sensor?
I would definitely like to DIY this problem since the dealer seems to want 800+ for this job. Is this job doable with minimum hardware and no lifting tool? Any source/brand of reliable O2 sensor would be appreciated. Thanks in advance.
Malfunction Indicator Lamp (MIL) came in a few days ago, and I realized a definite decrease in MPG and engine performance.
I had Autozone run the OBDII test on my A6 2.8 and the diagnostic gave me the following result.
<Troubleshooting P0056>
HO2S22 Heater control circuit
explanation: open or short circuit condition
probable cause: 1) poor electrical connection, 2) failed HO2S
message: 'PCM has determined that a malfunction exists in the heater control circuit for O2 sensor 2 in bank'
I read the tech article 'diagnosing O2 sensor heater code', but my error code (P0056) doesn't seem to be in the code table. But googling shows that P0056 represents 'DTC P0056 HO2S Heater Circuit Bank 2 Sensor 2'
So, am I certain that B2 S2 sensor IS the problem? Could the problem be coming from elsewhere?
a_o_smith's 'O2 sensor replacement' posting shows good picture of the location of the sensors and the plugs, but is there any tech article on replacing the O2 sensor?
I would definitely like to DIY this problem since the dealer seems to want 800+ for this job. Is this job doable with minimum hardware and no lifting tool? Any source/brand of reliable O2 sensor would be appreciated. Thanks in advance.
AudiWorld Super User
Joined: Aug 2002
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From: Warwickshire
I do not think you will need a "lifting tool", o2 sensors only weight about.....
the same a dohnut!
No, really, it seems strange that sensor 2 has caused a fuel economy issue as it is only there to monitor the efficiency of the cat and plays not part on mixture control.
No, really, it seems strange that sensor 2 has caused a fuel economy issue as it is only there to monitor the efficiency of the cat and plays not part on mixture control.
Tech Guru
Joined: Oct 2002
Posts: 34,430
Likes: 130
You will need to jack the car up to get to the secondary O2 sensors.
As Edd says, don't expect any change in performance; these sensors have nothing to do with performance.
Remember, the codes are not to be taken at face value. The ECU knows that there is an issue with a particular value that it sees from B2 02; the problem could be a bad sensor, but there could be something else causing the problem. I'd also check the cat to make sure it isn't deteriorating internally.
Remember, the codes are not to be taken at face value. The ECU knows that there is an issue with a particular value that it sees from B2 02; the problem could be a bad sensor, but there could be something else causing the problem. I'd also check the cat to make sure it isn't deteriorating internally.
AudiWorld Super User
Joined: Mar 2005
Posts: 6,134
Likes: 1
I thought that myself, but we looked it up in the Audi Motronic book & 2ndary can
affect fuel mixture. I guess if they see a constant, but high voltage from the rear o2 they will lean out the fuel trim.
AudiWorld Super User
Joined: Mar 2005
Posts: 6,134
Likes: 1
Unless the wiring is damaged or the connection poor, replace the O2 sensor
you may have to jack it up to disconnect the sensor from the exhuast, the hardest part is all the clips & zip ties holding the harnesses together that run on top of the transmission. It may be easier to take them both out together.
Thread Starter
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Joined: Jul 2006
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my city MPG seems to have dropped to about 14.1..
and I could definitely see a drop in MPG by looking at the 'instantaenous MPG reading' on the panel.
Also, when I step on the gas for quick acceleration, the revving doesn't seem to be as strong or reponsive as before.
Also, when I step on the gas for quick acceleration, the revving doesn't seem to be as strong or reponsive as before.
Thread Starter
Audiworld Junior Member
Joined: Jul 2006
Posts: 198
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tracking the B2 S2 sensor...
i see that one end of the B2 S2 sensor is located below the coolant reservoir (connected to the plug) and the other end is connected to the CAT.
i tried to track where the B2 S2 wire is leading down to, but couldn't reach it with my hand due to many wires/rubber pipes blocking the way.
how do you actually replace and route this thing?
i tried to track where the B2 S2 wire is leading down to, but couldn't reach it with my hand due to many wires/rubber pipes blocking the way.
how do you actually replace and route this thing?
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