Troubleshooting CEL, I need verification.

[katz]

Hey,
I have a CEL on and it wouldn't communicate with the scanner. So I used an analog voltage meter hooked up to pins #1 and #12 (Positive on #1). I have this process repeating: 1 short voltage sweep and then 3 larger sweeps. According to Haynes manual this is Intake Air Temp. Sensor. This book also said that you test the wiring for that the same way as the actual air flow meter. I hooked up the positive lead to pin#3 on the maf housing connector and it read 12 volts. This means the wiring is good. Now they said that if the wiring is good, then you need to replace the entire maf assembly.

Can anyone verify or correct any of what I'm saying.
Thank you and sorry for the long post.
Katz

 

[95 'clipse RS]

you also need to measure the signal output, measures between 4.5 to 5.25 with the key on. also run the signal voltage measuring all the way back to the ECU to make sure the signal is getting that far.

 

[akdsmer]

Pin# 3 at the MAF is the Battery supply voltage to the MAF which is what you checked. This is not used in the IAT circuit. The signal wire is pin #8 (at MAF). The Intake air temperature sensor pulls the reference voltage toward ground as the temperature rises (negative temperature coefficient). This lowers the voltage and tells the computer the temperature is warmer. The higher the temperature, the lower the voltage. This applies for the CTS (coolant temperature sensor) as well. If you disconnect the connector at the MAF you will see the reference voltage (it should be 5V). As soon as it's plugged in, the voltage will drop. I don't have a waveform for reference, but I'm pretty certain that you should see around 1.7-2.2 Vdc at warm idle. This is typical of MOST all vehicles.
If there is no voltage, then you need to go back to the PCM and check Pin 8 to make sure there is a reference voltage (5V) with MAF disconnected. If there is no voltage drop plugged in then run an ohms test across Pin 8 and 3 of the MAF and make sure there is not an open circuit. Let me know what values you see if you need more help!