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I have a 1998 Mustang GT that is getting a map air sensor low voltage code oh, p0102. When I hook the scanner up there is no voltage reading on the mass aircoming but if I hook up a voltmeter to the two signal wires at the sensor, I get a voltage reading. I also get a voltage reading if I check those sensor wires at the computer. The wires check out ok for continuity so I can only assume the the computer is bad because I have data, voltage, going back to the computer but it's just not seeing it. Am I correct in that assumption or am I missing something?
The sensor has 4 wires. Key on engine running I got red wire 12v. Black was ground. Voltage reading across the LB/R and T/LB was right around 1v at idle. If I rotate the throttle I would see the voltage go up on the meter. The scan tool showed 0v
Just a MAF then. 12v power and ground. Signal and signal ground. There is only one signal wire, but two grounds.
I would test again. With meter black lead to ground, check voltage on each wire at sensor and ecm.
ECM's are pretty hardy, so unless someone or something shorted the 12v into the signal wire the problem should be an open signal wire. Make sure the ecm pins are good, no corrosion and securely connected. WOT voltage on MAF signal should be 4v.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
I replaced the MAF from a running car and no change. I'll double check tomorrow but both signal wires ohm out fine back to the PCM. Does the PCM look at the voltage across those two wires or just one to ground?
Its only one signal wire for the MAF and that is what the ECM looks at voltage wise. It wants to see .09v 1v at idle and up to 4v at WOT on that signal wire. If you're getting voltage at the sensor but not the ECM that's where you have to concentrate, the wire between the two. You mentioned 0v at the ECM make sure you are looking at the MAF signal not the MAF signal ground. The scantool not showing MAF signal voltage is the problem. ECM's are expensive and really no way to test them so everyone hates calling an ECM as bad. Consider if you put in a new ECM and the problem is wiring, you could blow out the new ECM. Voltage testing is more reliable than Ohm testing. The voltages you want to see are 12v on power, .100mv on grounds and 1 to 4v on the signal at the sensor and the ECM.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
With the car running, I back probed the ECM connector and measured the voltage the voltage across the LB/R and T/LB and got 1.0V at idle.
I had the Forscan software running at the same time and the MAF V_V was showing 0.0V. eventually the software will show a MAF fault, check engine light will come on (p0102) and engine will die.
A little back story......This ECM is a replacement ECM because the original one had no control signal to the coils and car would not start. Purchased a "remanufactured" one, car started and ran but ran terrible and this is where I'm at.
A little back story......This ECM is a replacement ECM because the original one had no control signal to the coils and car would not start. Purchased a "remanufactured" one, car started and ran but ran terrible and this is where I'm at.
Remanufactured. You got a bad one. Return it.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
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