MAF and O2 Sensors
 

Well, I just got a hell of a shock. We sent our '98 ML320 into the shop (indie) for a service which should have been plugs, belts, hoses, and fluid change for $500 and came out with a $1600 bill. Part of this was to change all four O2 sensors and do the frount brakes.

Now the frount brakes and upgrading the fuel filter I can understand but the O2 sensors throw me for a loop.

A couple of month ago, I went in with a CEL and it was diagonised as a bad MAF....OK that makes sense....and it was changed. Since then, I have not had a CEL but when I took it in this time, the mechanic said that when they did the CEL, it also indicated that the O2 sensors were bad but they didn't replace them at that time. (don't know why).

My question is: If the O2 sensors were really bad, shouldn't I have had a CEL even after the MAF was replaced? Is there a way I can verify the sensor condition when they are off the car.

tks for any input.

If the o2 sensors were bad they should have set off the CEL. How much did you drive it in the two months between visits?

Since the MAF was replaced, we probably drove ~1500 miles. Fuel economy seemed OK per the trip computer, averaging 22.1 combo.

I spoke with the shop about this some more and asked if they pulled codes yesterday when I took it in and was told....No, we went by the previous codes with the bad MAF. I think the shop is feeling like they were wrong as I was informed that they cancelled $500+ charge for the O2 sensors.

Don't you just love a shop that does the right thing. I didn't even ask for the charges to be reversed....but it was on my mind.

When the MAF/AMM goes bad it makes the O2 sensors look like they are reading out of range which leaves a fault code. I'd be more concerned that they installed such an expensive component without calling you first for your approval. :eek:

Yes, we did have a conversation about that very point. I doubt this will be a problem in the future.