2002 S80 Oxygen Sensor

puntmeister · Post by **puntmeister** » 20 Mar 2015, 22:06

I got scan code ECM-290A (Front Driver-side oxygen sensor, as far as I can find).

Using an Icarsoft i906, I can ready the oxygen sensor datastream. However, I can't make sense of the readouts.

For the rear oxygen sensors, they seem to make sense - steady around 0.6 volts. Initiate a vacuum leak, and voltage drops to near 0.0.

However, the front oxygen sensors read steady around 0.90. Initiate a vacuum leak, and read-out goes to as high as 5.0!

My understanding was O2 Sensors data ranged from 0.0 to 1.0 volts. What does a reading of 5.0 mean?!

Perhaps the front 02 sensor data isn't volts. Anybody have an idea what these readouts are?

And what the readouts should ideally be?

I don't want to change sensors/catalytic converter/etc if they aren't truly bad.

draser · Post by **draser** » 21 Mar 2015, 12:56

Front o2 sensor is wide band, and reads 1 lambda for a good running engine. Lambda is the ratio of air to fuel, and 1 lambda is 14.7 parts of air to one of gas, called stoichiometric ratio. Don' t ask how they come up with that name. Anyway, your sensor seem to be working, however the problem is it reads .9 and the range should be +/- 0.02%, thàt is .98 to 1.02. So I'd take another reading and look at all digits, better yet post here. Also post fuel trims to corelate with o2 sensor reading.

puntmeister · Post by **puntmeister** » 22 Mar 2015, 22:17

After exhaustive Googling (without the benefit of having read your response) I found out exactly what you are saying - 02 sensors read 0 - 1 volt, wide-band sensors vary depending upon manufacturer, but European models are typically 1.0, with less than 1.0 being rich, and greater than 1.0 being lean.

I tested again - wife driving, me watching the readouts. The front sensors toggle tightly around 1.0 (0.98 to 1.03 during steady cruise). One rear sensor toggles between 0.1 and about 0.7. The other mostly stays close to 0.7. Guessing the cats are bad (I got codes for bad cats as well). The sensors themselves seem fine - but I suppose the system is checking for very specific tolerances, which I can't catch.

What rear 02 readings would new/good catylitic converters read? Really don't want to be hit with exhorbitant cost of new cats if avoidable.

draser · Post by **draser** » 23 Mar 2015, 05:32

Looks like the problem is with the cat on the one side that switches between .1 and .7. That's where the cat code comes from. Could use a plug anti fouler bushing to remove sensor from stream and code will go away. Front sensors seem fine. The rear sensor that hangs around .7 volts shows the good cat. If cat code is all that's wrong with your car you've found your problem. However, question is why the one cat went bad. It may be just normal wear, or engine runs rich which caused cat to go bad. One way to see that is looking at your fuel trims, if they're double digit negative you're running rich.

puntmeister · Post by **puntmeister** » 23 Mar 2015, 20:39

OK, another test drive:

LTFT, bank 1: +17.2%
LTFT, bank 2: -5.5%

STFT (both banks) - all over the board, but rarely above 5%

Front O2, bank 1: .90
Front O2, bank 2: 1.10

Rear O2 bank 1: .05 v
Rear O2 bank 2: .70 v

Bank 1 is the passenger side?

Some history:

1) Just replaced spark-plugs - had autolites, replaced with Volvo plugs. No blatant signs of fouling/over-fueling/excessive lean on old plugs.

2) Bought car a little over a year ago - idle was bad. Immediately replaced the PCV, which had a ruptured diaghragm, causing vacuum leak/rough idle. Idle was immediately better.

3) Have had various emissions codes before/after PCV change-out. Sensors bad, cats bad, LTFT off.

Unplugging MAF results in immediate rough idle.

Can't find any vacuum leaks. Removing brake-line vacuuum results in immediate rough idle (same as when PCV was bad).

Recently had injectors cleaned (on car). No noticeable change in performance.

Individually pulling distributors results in immediate performance drops (all cylinders firing).

Idle seems fine, acceleration fine - although, I didn't own car from new, so can't tell if it is deteriorated from 'normal'.

Timing belt seems to have a bit more play than I'd think it should - but I don't have a ton of experience to base this on....

175,000 miles....

puntmeister · Post by **puntmeister** » 23 Mar 2015, 21:00

1 thing - during this test, I think the Front Bank 1 sensor was in open loop (scanner shows readings, but car not using data to adjust fueling?).

Front Bank 2 was in closed loop.

draser · Post by **draser** » 24 Mar 2015, 12:30

Fuel trims show bank 1 running lean, and bank 2 okay unless it' trending up. For now I'd focus on bank 1. O2 sensor one being .9 indicates a rich mixture but does not correlate with fuel trim. Two posibilities: wrong sensor or defective sensor. I'd double check make sure it's correct sensor for bank 1, if yes I'd swap sensors to see readings. Why do you think bank 1 is in OL? Not sure which bank is 1.

puntmeister · Post by **puntmeister** » 24 Mar 2015, 13:29

Yeah, I couldn't make sense of rich reading, with lean fuel trim. Perhaps the ECU is smarter than I give it credit for, and the bad sensor codes are accurate.

I went ahead and ordered two new front sensors. Quite possibly changing out perfectly good sensors - but I don't know another sure-fire way to make certain the sensor data itself is accurate. If the sensors/data itself is bad, everything else seems to be a wild-goose chase.

There is a check in my scanner, which shows if open/closed loop for the front 02 sensors. The Bank 2 showed closed, Bank 1 open - but that was at one moment in time.

Will see what kind of data new sensors report....

draser · Post by **draser** » 25 Mar 2015, 07:16

Since there's a doubt on bank one being O/L I'd take another set of readings for trim and sensor. If you create lean/rich conditions and sensor responds chances are it's working.

puntmeister · Post by **puntmeister** » 28 Mar 2015, 17:06

Got the O2 sensors, set about to replace them - but first disconnected battery. I had read its a good idea to zero-out the LTFT when making engine repairs.

Couldn't replace one of the sensors - wrong model (only difference is a tiny piece of plastic on the plug attachment - right side versus left side blip). Happened to be on the side in question, so didn't bother replacing either sensor.

However, ran the car, with no changes other than zero LTFT (disconnecting battery worked). Readings now:

STFT - both waffle slightly negative at idle (-3)

Front O2 sensors - both stay very close to 1. Only vary to around 0.99.
Rear O2 sensors - both steady around 0.50

I never zeroed-out the LTFT back when the car was idling lean due to a bad PCV. Perhaps all this mess has just been due to the LTFT being out of whack?

Will drive/test some more.