94 Explorer New MAF but still showing code 157
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94 Explorer New MAF but still showing code 157
I have a 94 4WD Explorer that started running horrible. I bought a ODB code reader and it threw Codes 157,158, and 159. So I went to Checker and bought a new one but it did no GOOD... I'ts still running horrible and throwing a Code 157 ??? Could I have bought a NEW FAULTY MAF Sensor or is there something more??? I am on the verge of a nevous breakdown? PLEASE HELP !
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From: UT
Remember that codes point to problems in circuits, of which the sensor is only one part. Are the codes KOEO hard fault codes, KOEO soft fault (aka CM codes), and/or KOER codes? Which type of code you get determines which part of the diagnostic tree to start at.
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Ok, The code "157,( C )" Mass Air Flow Sensor fault, low voltage, is the KOEO test. Before I purchased the FORD OBDI Code Reader, I replaced the fuel pump and The fuel injector pressure regulator and I also had the catalytic convertors checked and they were fine.. I attempted to run the KOER test but it read Code "998" Failure Mode and I was told I had to take care of the KOEO problem 1st.. I honestly don't know if that is true or not.
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My information indicates that a 157 can't be a KOEO code, so I will assume it is a CM code (after the separator pulse). A KOER 998 indicates that the 158 and/or 159 were KOEO codes (or at least should have been).
Since you've replaced the MAF, we'll assume it is good for now (though one should never discount the possibility of getting a bad part out of the box). This suggests that the problem is most likely in the wiring between the MAF and the PCM.
This may be over your head, but in electronic terms, the MAF is a basic wheatstone bridge set up. You have a source voltage to the bridge (battery voltage, the red and black wires to the MAF, pins A and B according to my wiring diagram), and you have a meter reading the voltage across the bridge (MAF signal and MAF return leads C and D).
If were devising my own circuit test, I'd start by checking that the MAF was getting power from the EEC relay and had a good source ground. then check the signal wires from the MAF to the PCM for continuity and for shorts to power and/or ground. If that checks out, I'd put a voltmeter across the signal wires (backprobe) and see what I was getting for a signal, and see if it was reasonable.
Since you've replaced the MAF, we'll assume it is good for now (though one should never discount the possibility of getting a bad part out of the box). This suggests that the problem is most likely in the wiring between the MAF and the PCM.
This may be over your head, but in electronic terms, the MAF is a basic wheatstone bridge set up. You have a source voltage to the bridge (battery voltage, the red and black wires to the MAF, pins A and B according to my wiring diagram), and you have a meter reading the voltage across the bridge (MAF signal and MAF return leads C and D).
If were devising my own circuit test, I'd start by checking that the MAF was getting power from the EEC relay and had a good source ground. then check the signal wires from the MAF to the PCM for continuity and for shorts to power and/or ground. If that checks out, I'd put a voltmeter across the signal wires (backprobe) and see what I was getting for a signal, and see if it was reasonable.
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Similar MAF issues
My information indicates that a 157 can't be a KOEO code, so I will assume it is a CM code (after the separator pulse). A KOER 998 indicates that the 158 and/or 159 were KOEO codes (or at least should have been).
Since you've replaced the MAF, we'll assume it is good for now (though one should never discount the possibility of getting a bad part out of the box). This suggests that the problem is most likely in the wiring between the MAF and the PCM.
This may be over your head, but in electronic terms, the MAF is a basic wheatstone bridge set up. You have a source voltage to the bridge (battery voltage, the red and black wires to the MAF, pins A and B according to my wiring diagram), and you have a meter reading the voltage across the bridge (MAF signal and MAF return leads C and D).
If were devising my own circuit test, I'd start by checking that the MAF was getting power from the EEC relay and had a good source ground. then check the signal wires from the MAF to the PCM for continuity and for shorts to power and/or ground. If that checks out, I'd put a voltmeter across the signal wires (backprobe) and see what I was getting for a signal, and see if it was reasonable.
Since you've replaced the MAF, we'll assume it is good for now (though one should never discount the possibility of getting a bad part out of the box). This suggests that the problem is most likely in the wiring between the MAF and the PCM.
This may be over your head, but in electronic terms, the MAF is a basic wheatstone bridge set up. You have a source voltage to the bridge (battery voltage, the red and black wires to the MAF, pins A and B according to my wiring diagram), and you have a meter reading the voltage across the bridge (MAF signal and MAF return leads C and D).
If were devising my own circuit test, I'd start by checking that the MAF was getting power from the EEC relay and had a good source ground. then check the signal wires from the MAF to the PCM for continuity and for shorts to power and/or ground. If that checks out, I'd put a voltmeter across the signal wires (backprobe) and see what I was getting for a signal, and see if it was reasonable.
I’m hoping someone can help with this. I have a similar issue as above on my 1995 F150. I checked the four wires (ABCD) and had voltages of A - 11.8, B 11.8, C 3.05. I was unable to check D because the truck won’t stay running long enough to get to temp (which I read was necessary to have a proper test)
does the C voltage need to be 12V as well? If this is the issue, what would my next step be?
thanks again for ANY insight, I’m learning as I go between these forums and YouTube
thanks
Last edited by Jrod34; Jan 11, 2021 at 11:57 AM. Reason: F150
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