Mass Airflow Sensor bad?
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Mountain Pass
Joined: Dec 2002
Posts: 168
Likes: 1
From: Rochester
Mass Airflow Sensor bad?
Greetings all. I have a '94 Explorer Automatic Trans, 105,300 miles. All of a sudden it started running terrible. The check engine light came on, the exhaust smells awful and it's spewing carbon out the tailpipe. I'm getting a code 157 - "Mass Air Flow signal low or grounded" I've tried cleaning the filaments with no help. Anyody got any ideas other than changing the Mass Airflow Sensor?
Thanks all.
Thanks all.
Postmaster
Joined: Dec 2001
Posts: 3,742
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From: UT
Computer codes point to problems in a circuit, not necessarily at any individual parts in that circuit. Problem might be a bad sensor, but it could just as easily be a bad connection between the computer and the MAF, a bad reference voltage, a bad excitation voltage to the MAF, Air getting in through another route other than the MAF (such as if the intake tube were disconnected).
1st question: Is this a continuous memory code? If so, did you get pass codes for both the KOEO hard faults and the KOER test?
If this is the only code, then start by carefully inspecting the wiring. Make sure there are no obvious breaks/bad connections/etc.
Then, get a wiring diagram (so you know what wire is what) and make sure the MAF is getting battery voltage at the appropriate leads. Make sure the Vref has ~5 volts. This is where a good pinpoint or circuit test comes in handy.
1st question: Is this a continuous memory code? If so, did you get pass codes for both the KOEO hard faults and the KOER test?
If this is the only code, then start by carefully inspecting the wiring. Make sure there are no obvious breaks/bad connections/etc.
Then, get a wiring diagram (so you know what wire is what) and make sure the MAF is getting battery voltage at the appropriate leads. Make sure the Vref has ~5 volts. This is where a good pinpoint or circuit test comes in handy.
Thread Starter
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Mountain Pass
Joined: Dec 2002
Posts: 168
Likes: 1
From: Rochester
Thanks Mr. Shorty. The 157 code comes in from both the key on engine off and engine running test. I'm also getting a "998 Did not pass KOEO Test."
Thanks for the tip on voltages, I will check them tomorrow.
Thanks for the tip on voltages, I will check them tomorrow.
Thread Starter
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Mountain Pass
Joined: Dec 2002
Posts: 168
Likes: 1
From: Rochester
157 Comes in as a hard fault and with the engine running.
I checked the wires at the connector......
heres what i get....
A Red 12 Volts
B Black / White stripe Ground (checked with ohms to neg. battery post, also measured 12 V between A & B)
C Tan / Light Blue stripe 5.97 Volts (Exciter?)
D Light Blue / Red Stripe O Volts
Thanks alot for your help...
I checked the wires at the connector......
heres what i get....
A Red 12 Volts
B Black / White stripe Ground (checked with ohms to neg. battery post, also measured 12 V between A & B)
C Tan / Light Blue stripe 5.97 Volts (Exciter?)
D Light Blue / Red Stripe O Volts
Thanks alot for your help...
Postmaster
Joined: Dec 2001
Posts: 3,742
Likes: 2
From: UT
I can't remember for sure, but C and D don't look right. As I recall, the voltage between the MAF return pin and ground should be ~0.6 V at idle, and should increase with increased throttle opening/engine speed. Could indicate a bad MAF, but I'd get a hold of a proper circuit test before coming to that conclusion. They can often be had in Mitchell manuals in the reference section of many libraries.
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Mountain Pass
Joined: Dec 2002
Posts: 168
Likes: 1
From: Rochester
I tried tapping on it when I got to work this morning, on my way home it actually ran OK (no check engine light) for a few miles. The voltage readings I got where with the key on , engine off, and the connector unplugged so I think they make sense. I will try later to get them with everything running.
Thanks again for the help!!!
Thanks again for the help!!!
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