Question about Volvo 850
Mechanic changed the rear oxygen sensor and I was told that should never be touched. what is going to happen to my car
The rear oxygen sensor is used to imply catalyst damage has occurred. This is done by having an upstream (front) oxygen sensor and a downstream (rear) oxygen sensor. The front sensor will jump quickly between .1 and .9 VDC generally and the rear will do so much more slowly. If the rear sensor\'s activity closely mirrors that of the front, one could imply that catalyst damage has occurred (such as during a prolonged misfire condition where large amounts of unburned fuel enters the catalyst and overheats it), puts the system out of closed loop operation and turns on the MIL.
The details below do not cover all possibilities here, just the most common ones that I have seen over the years;
Usually, that sensor is replaced when a MIL code is set for \'catalyst inefficiency\' is set. This is the first step to ruling out the catalyst as truly being failed. Unless another code is set and the MIL is turned on, nothing strange should happen to your car.
To check, connect an OBDII scanner to your car and look for P0130 codes (o2 sensor failure), P03xx codes (misfire conditions) and catalyst codes (see your manual for the exact codes). Taken together along with the freeze frame data, have the vehicle smog tested. Smog testing just checks for high VOC output along with CO output (CO is not a VOC). One could then assume that the catalyst or other emission control system could be at fault.
Other things that could cause this are lean/rich codes (generally P0172) indicating the MAF is dirty or faulty. Always check and clean the connector going to the MAF before condemning it and clean the MAF itself with MAF cleaner (not brake or electronic cleaners, they are too hard on the film) and see if the performance improves.
Posted on Jul 16, 2014
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Posted on Jan 02, 2017
SOURCE: oxygen sensor keeps going bad,
It could be the problem or he just wants to make a lot if money. I had a similar problem and it turned out to be electrical. I had another component out that caused an abnormal electrical condition, it could be happening to you. Check to make sure the sensor is within it electrical limits, (volts, amps, and ohms) and then refer to your vehicles electrical schematic to find relative components within the system. Don't go rippin into you motor, yanking off the heads, until you eliminate the problem as being electrical. get a good multimeter and remember, its only a 12v system. good luck
Posted on Aug 15, 2008
fist unclip wire,then unscrew it with a 28mm spanner ,fitting procedure is the reverse .It turns anticlockwise to unscrew and clockwise to screw up ,torque setting is a grunt and two scuffed knuckles and max of 3 swear words
Posted on Jan 01, 2009
The O2 sensors are located in the exhaust piping.
One (bank 1) is on the engine side of the Catalytic convertor.
Second (bank 2) is on the other side (exhaust end).
There are manufacturers that make universal fits that will go in either location. Be sure to specify the rear sensor when you go to the parts store.
It will look like this....
It threads right into the exhaust pipe.
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Posted on Mar 05, 2009
If it was the mass air flow sensor, you will have a check engine light. The small rubber hoses connected to/from the mass air flow connector might have come loose or have a crack, which will cause compression to be too low. Check there before replacing the maf sensor.
Posted on Aug 27, 2009
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