Can anyone provide some insight into the possible causes of a mass air flow sensor DTC 48? I'm running a stock LT1 in my Caprice with an F-Body MAF sensor. I've modified the stock tune by copying over the MAF table values from a stock F-Body tune. I've tried two different MAF sensors, as well as verified the correct voltage at the harness. Are there any other potential causes of this code? The car runs and drives alright in speed density mode, but in Datamaster the AFGS remains pegged at 343.

 

Check the voltage between the pink wire and the black/white (ground) wire in the MAF harness connector. Should be 12V. If you have 12V on the pink wire then measure the frequency across the yellow (signal) wire and the black/white wire. Should be about 2,800 Hz at idle, and increase exponentially as air flow rises.

 

What specifically is the PCM looking for when tripping this code? If I clear it, it returns immediately. Does this indicate the problem is definitely with the MAF? I can't find any vacuum leaks, and the MAP at idle is 30 kPA. The LT trims after idling for 10 minutes are in the mid 140's.

 

Its looking for any kind a signal that varies, and does not stay constant. If the MAF sensor isn't working the signal doesn't move, and the code sets for a static frequency. They didn't add a "rationality" check (MAF measurement within a fixed percentage of the speed-density calculated flow) until 96 with OBD-II.

If there is no MAF activity, the PCM defaults to speed-density mode, and calcualates the mass air flow rate from the RPM, displacement, absolute inlet air temp, MAP and a value picked off the volumetric efficiency table based on engine load and RPM.

 

So I finally tracked down the problem. The wires in the MAF extension harness were backwards. The signal and power wires did not match up between the engine harness connector and the MAF connector. I previously had this extension harness on another car and never had an issue, so I'm not sure what was happening there.

 

I had the same problem this spring.I replaced the pigtail connector but had the wires in their wrong places.I now have them correct & the code hasn,t reappeared since.