mass air flow question 99 Impreza

[aa8jzdial]

1999 Impreza

CEL and driveabilty issue.

 

Code reader says "Mass air flow sensor input low."

 

Checking the output sig from the MAF (under the hood) shows from 1.4 volts dc at idle about to about 2.5 volts while mildly revving the engine.

My thinking is if the reader is correct the wiring harness must have a break somewhere.

The trouble is I do not have the schematic indicating which pin to check on the ecu to verify if the MAF signal is or is not getting to the ecu.

Can any one help?

thanks

Rick

[Legacy777]

This is for the 98 Impreza, but should be close if not the same.

 

http://main.experiencetherave.com/subaru_manual_scans/FSM_Scans/1998_Impreza_ECU_I-O.pdf

[aa8jzdial]

Thanks for the quick reply Josh and the concise info.

I think there may be a difference between 98 and 99 vintages as I recall seeing 4 wires going to this MAF sensor rather then 3 as referenced on the 98 schematic. Even so I will check these pins.

 

I beleive I will snoop around a bit more by comparing the signal coming out the troubled MAF sensor with the signal coming from the MAF sensor on my 99 Forester.

 

I found that removing the connector on the Impreza MAF sensor the car will cough and die.

That is getting me thinking that maybe there is not a funky connection to the ecu MAF input.

 

More digging.

rick

[Legacy777]

Yeah the car will not run with the MAF sensor disconnected.

 

The maf sensor itself only should have 3 wires going to it, ground, signal, and voltage supply. The newer MAF's may have an additional wire for temperature, but that's just a guess.

 

The older MAF's found on the first gen legacies had all five pins, and that was due to there being two different MAF sensors. The ECU had a trigger that when grounded would tell the ECU that it is the incorrect MAF sensor for that car.