My check engine light is on again. I just had my pre-cat O2 sensor changed for the second time. Should it be going bad so often? I paid $280 the first time and nothing the second because it was under warrenty. The mechanic cant keep replacing the sensor forever. Can something else be killing the sensor?? any help appreciated.

2003 SLK230 Kompressor with 61K miles.

 

Try checking your MAF sensor.

 

Hi,
O2 sensors are extremely reliable.
They do go defective but the chances of 3 in a row is very unlikely unless they all came from the same batch.
So they could be being damaged in Service, be faulty components or alternatively are not faulty.
Changing an O2 sensor can correct a problem for a short period of time but not actually be the cause of the problem in the first place! New components (with slightly different characteristics) can potentially effectively hide / offset other defects.

Poor fuel can kill O2 sensors just like catalysts.
Here in the UK there has just be a MAJOR problem with the supermarkets selling fuel with Silicon contamination (this is used in diesel fuel to stop foaming) and thousands of cars all had O2 sensor fail at the same time, then there weren't any sensors etc. so is your fuel OK? Will cost the supermarkets multi million pounds!
Poorly maintained or worn engines can also cause problems.

I suspect however that your O2 sensor wasn't faulty although changing it appeared to correct the fault.

Before changing an O2 sensor the Diagnostic codes should be read that caused the CEL Check Engine Light to come on. This should indicate an O2 sensor problem. If not it is unlikely to be the O2 sensor at fault.
The waveform output from the sensor should be observed to confirm incorrect voltage or cycle time characteristics which are obvious to a trained technician.

Bottom line.
It is more than likely that the O2 sensor is not the cause.
What other symptoms did you have other than the CEL light which can illuminate for thousands of reasons including a gas cap not fitted.

It could well be the MAF at fault (but it could also be many other defects) but the key is WHAT WERE THE OBD DTC codes? If this was in line with an O2 sensor failure was the waveform confirmed as incorrect? If so you have got contaminated fuel problems or alternatively your engine is in real bad shape (uses lots of oil?).

Hope this helps.

Stuart

 

Always get the MAF cleaned or substituted 1st esp if its runs poorly.
Gas cap is a good 2nd for cel.

Codes can be spurious after a maf plays up. From plugs to O2
Get codes cleared and see what gives over the next period of time.

Readaption of ME can be useful if have the equipment.

Bazzle