MB-BOB

A couple weeks ago, I changed the oil on my C320, and while at this, I also cleaned out the airbox, and sprayed the Mass Airflow Sensor at the central plenum intake with MAF cleaner spray. I sprayed the MAF while the engine was running, which I think was a mistake. I've sprayed the MAF before (at 42,000 miles) but I guess the engine was off. Can't remember.

Anyhow, the Check Engine light came on. And even though the car performs great, the light wouldn't reset overnight. I took it to a Pep Boys and had the OBDII reader put on it. Code PO170 and PO173 (fuel trim) alerts, which I expected, since I was liberal in spraying the Cleaner on the MAF. We reset the codes, and the car started and ran normally. No codes.

A week and 200 miles later, the Check Engine Light returns... Hmmm...

Although my air filters have only 25,000 miles on them, and they weren't very dirty, I put the leaf blower to the air filters to blow away most of the dust when I cleaned out the airbox. I have done this before as a mid-life air filter maintenance. I reinstalled the filters moving what was the trailing edge of the pleats to the front of the airbox. I think this exposes the clean side of the pleats to the airflow. Again I've done this before without problem.

I can't imagine that spraying the MAF did anything to the O2 sensors, which is also indicated as a possibility with the 170 and 173 codes. My car has only 74,000 miles on the odo.

Car works just fine, but I'd like to figure out how to make these codes go away. Maybe I shouldn't clean the MAF in future... All I needed was an oil change, and I've created a problem trying to be proactive.

Any help appreciated.

Dingleberry

pure coincidence. the o2 sensors showing up as faulty need to be replaced.

edit: just reread your post. apparently you're trying to say that the codes you pulled are not for o2 sensors but you speculate that they are related. therefore i take back what i said. is each code for the left and right banks respectively? if so, then i doubt both o2 sensors went bad at the same time. perhaps you destroyed your MAF sensor. maybe see if anybody nearby you is kind enough to swap maf sensors for a few days...

SeaCoupe

I would reset the light, and try again.

If you need an o2 sensor, it is likely only the first on that is needed.

Ed

MB-BOB

Do the O2 sensors have any effect on driveability? I have noticed no change in engine performance, and my gas mileage has not changed at all.

mleskovar

Both the MAF and the O2 sensors have heaters that keep them at operating temperatures. They both also have thin and precise coatings they rely on to get input for changes in fuel/air mixtures. I'm guessing the cleaner sprayed on a hot MAF could affect it. I doubt the cleaner would hurt the O2 sensors but I've been wrong before.

mleskovar

I was going to ask you these questions.....generally you would notice a change in performance or gas mileage with bad O2 sensors.

MB-BOB

Well, I had the check engine light reset, drove it 140 miles then it reappeared. I have reset it a second time. We'll see.

Lenin

Did you read the codes every time? It is not clear if you are getting the same codes or not.

mleskovar

I've read where you can take voltage measurements at different connections for the MAS and the O2 sensors to determine if they were OK. If the CEL continues and you have a DVM and some patience you might try it before throwing parts at it.

Glyn M Ruck

P0170 = Fuel Trim Malfunction (Bank 1)
P0173 = Fuel Trim Malfunction (Bank 2)

You almost certainly need a new MAF. Hot wire MAF's cannot be sprayed with MAF cleaner while operating. It cools them too quickly which places immense stress on them usually leading to failure. You need to correct fuel trim or you will shorten the life of your O2 sensors. O2 sensors usually go 80-100,000 miles before they cycle too slowly.

I hope you have not sprayed any cleaner or similar containing silicone anywhere near the inlet system? If you have and the engine ingests it you will immediately poisen the O2 sensors. Shot O2 sensors should cause slight engine stumble.

Change the MAF - Good luck