Thread: MAF problem - need diagnostic help...

My 96 3.1 is running well, but it threw two codes today:

P0102 - MAF Circuit Low Input

P1655 - Evap Solenoid Control Circuit

As usual, the Gates manual is useless.

My scanner can log real time data. The MAF signal is .26 and doesn't change while driving. All the other obvious signals seem reasonable - MAP, TPS, RPM, Temps. etc. and change with speed and acceleration. However MAF signal doesn't change.

Is this what the computer does (assume a constant value) if the MAF doesn't send a signal or sends a signal out of tolerance?

Is there any way to tell if my MAF is bad or my wiring is bad?

Anyone know if the Evap Solenoid code means the evap solenoid is actually bad, or is it an accumulated error code? If it's bad, where is it?

Thanks to all...

Boatman.

Put in a new MAF from Auto Zone, but the computer still throws the same codes and my scanner still reads a constant MAF output value of .26 while driving. The car does not start correctly dies once or twice and hunts at idle for about a couple of minutes. Drives OK after that.

It still throws the Evap solenoid circuit too.

Is there another problem that could be causing the car to incorrectly read the MAF or substitute a constant value for it?

This is getting confusing.

Thanks...Boatman.

Usually when sensors go bad (or unpluged) they read 99 on the scanner.

I know this for a fact that the iac and the map does.

On a thread from another forum, I learned that there should be 12 V plus going to the MAF:

Pink = Batt +
White/Black = Ground
Yellow = voltage out

Well, the white/black is a good ground, but I'm getting no voltage to the pink wire. I'm thinking this is the root of my problem.

Anyone know why that 12 V source would all of a sudden go bad?
Anyone know if anything else is on that 12 V circuit?
Anyone know if the computer supplies voltage or the key/ignition circuit does?

Any help greatly appreciated.

Thanks...Boatman.

This is starting to become clearer. Went through the wiring diagram and found that the MAF and Evap purge solenoid both share the same "pink wire" 12 V source. And my car is throwing both MAF and Evap codes. It's got to be the 12 V source.

Wiring diagram says that the source is the "Underhood Electrical Center 1". But is does not show that the source from the PCM is fused, just that is passes through this box.

Anyone know if it's fused?

Anyone know where the Underhood Electrical Center 1 is?

Thanks...Boatman.

could it be a bad pcm?

Turns out that the two codes I got - one for low freq for the MAF and one for the Evap purge solenoid - were both caused by a blown fuse 12 (in the fuse box on the front passenger side under the front brace). Once I saw that both were on the same circuit, I know that was the problem...and it was.

Why the fuse blew is another matter. It was a self inflicted wound. I didn't like the fact that the radiator fan doesn't come on until 230 so I wired in a Flexalite adjustable thermal switch from the radiator into the fuse box to the fan relay. My problem arose when I misread the wiring diagram. I know that the two-wire thermal switch feeds the PCM, which in turn powers the relay. However, I mistakenly thought that the two wire switch was a positive fed resistor, like most two-wire thermal switches are. You know, positive voltage in and increasingly positive voltage out as temp increases. Well, it's not. It's a negative in and out.

With this wiring mistake, every time the fan went on I shorted fuse 12 and the car ran poorly - hard to start and hunting idle. Once I figured this out, I ran ground-in to the adjustable switch and then onto the fan relay (brown wire) and everything works great. I cleared all the codes and the car runs just fine. I used my scanner to set the fan to come on when the engine coolant hits 200. Now I can sit in traffic on a hot day forever (tried this out today in some Memorial Day traffic) and the engine never gets above 200.

Thanks to everyone who posted and all the helpful advice.

This is a great board.

Boatman.