Hi folks, I've mostly been a lurker here on and off for 15 years. Here are the facts:

'98 F150 4.6L, 143K miles, original owner, all maintenance done on time, truck runs as good today as the day I drove it off the lot. Never had a check engine light before.

Last week, I replaced the engine air filter and hit the IAT and the other sensors in the intake with some MAF sensor cleaner.

100 miles later, Check Engine comes on. There was no obvious change in running or driveability, but was on a road trip and checked the mileage late that night - it was down nearly 4-5mpg from my usual 19 all-highway.

Tonight I finally had time to pull out the code reader. Two identical entries were stored:And I recorded the following data with the engine warm:The only thing I noticed with the O2 sensor voltages is that O2S22 is far more stable and has a very small range of voltages compared to the other 3.

I cleared the codes and drove about 2 miles (not much of a test I know) and no additional codes were logged.

Does anything jump out here? Seems like an odd coincidence that this would happen so quickly after the air filter change/sensor cleaning, but stranger things have happened.

Any help is greatly appreciated!

Mike
Olathe, KS

 

Coincidental.

Probably time for a new downstream O2 sensor on the passenger side.

Depending on the particular fault, it often takes two fresh drive cycles in which an error occurs to set a MIL. Don't base data n short drives, give it several days, if needed.

If the same code comes back and you want to perform further diagnostics, swap the downstream sensors, reset the PCM, and see if, after a sufficient time, you get a P0161 error.

 

Thanks! So you're suspecting O2S12 even though the voltages on it are consistent with the others (in other words the PCM is detecting a problem with it that isn't voltage related)? And if there's a voltage drop on that sensor that is intermittent (i.e., I'm not seeing it with the reader), then I don't get the severe drop in mileage.

 

Heater ckt codes are almost always the sensor .

 

Also another dumb question. How do the O2 PID's map to the actual sensor locations? I would've thought O2S12 would be downstream driver's side?

 

O2S1x is bank 1, O2S2x is bank 2.

Bank 1 is the right hand bank as viewed from the driver's seat, bank 2 is the left.

Downstream sensors will not affect fuel economy, especially heater codes.

 

Bank one is pass side ,cyl 1-4 . Bank 2 is driver side cyl 5-8 .

 

Thank you both. I wonder what happened to my mileage. Guess it's time to turn it over to someone who knows what they're doing.