Check Engine Light
Thread Starter
Joined: Dec 2012
Posts: 10
Check Engine Light
1995 Ford Mustang V6 3.8L engine
I have the famous P0102 code. I have installed a new cold air intake but the code was there before i changed it. The car runs great. No sluggishness, no rough idling, no nothing. It runs great. I have cleaned the MAF with CRC Mass Air Flow Sensor cleaner. Other than the code, the car runs great. Any ideas.
I have the famous P0102 code. I have installed a new cold air intake but the code was there before i changed it. The car runs great. No sluggishness, no rough idling, no nothing. It runs great. I have cleaned the MAF with CRC Mass Air Flow Sensor cleaner. Other than the code, the car runs great. Any ideas.
Joined: Nov 2012
Posts: 27
From: California
1995 Ford Mustang V6 3.8L engine
I have the famous P0102 code. I have installed a new cold air intake but the code was there before i changed it. The car runs great. No sluggishness, no rough idling, no nothing. It runs great. I have cleaned the MAF with CRC Mass Air Flow Sensor cleaner. Other than the code, the car runs great. Any ideas.
I have the famous P0102 code. I have installed a new cold air intake but the code was there before i changed it. The car runs great. No sluggishness, no rough idling, no nothing. It runs great. I have cleaned the MAF with CRC Mass Air Flow Sensor cleaner. Other than the code, the car runs great. Any ideas.
Other than that I would probably try completely replacing the MAF but I'm no auto repair guy, you would think you would see obvious symptoms with the car if there was a problem.
Thread Starter
Joined: Dec 2012
Posts: 10
I cleared the code after i installed the CAI and i also cleared the code after i cleaned the MAF. Both times, the code came back. I even installed a new temp sensor and tried clearing it after that with no luck. Done everything that i know except check the voltage in it and replace the MAF. I just didn't think i would have to if the car was running good. Any suggestions ???
4th Gear Member
Joined: Nov 2006
Posts: 1,669
From: CA
There is some useful info here: http://www.obd-codes.com/p0102
Does your CAI use a K&N style filter (that is oily)? If so, the oil may have gotten onto the MAF and caused this fault.
The CEL means that the sensor is sending a lower then expected signal back to the PCM. A volt-meter or multimeter set to volts is all you need to test the MAF to see if it is bad but an oscilloscope is much better. Either way, there should be 4 wires going into the MAF sensor. According to my ’98 electrical diagnostics manual, the red wire should be a constant 12 volts. The black wire should be ground. Here is a quick way to test the MAF.
Remember this voltage (a.k.a. battery voltage). It should be between 12.4 & 12.8 volts. If not, charge the battery before continuing.
Test the power wire:
You should read within 0.5 volts of battery voltage. So if battery voltage was 12.6, you should read between 12.1 & 12.6 volts. Anything less then that and there is resistance on the power wire causing your problem. If you read 0 volts, wiggle the lead wires. If the reading changes then you are reading "ghost voltage”. Reset the safety pin, making sure it is making god contact inside the connector and try again. If the reading stays at 0 volts then there is a short to ground somewhere on the power wire. If the reading continues to show ghost voltage then there is a break in the power wire somewhere.
Test the ground wire:
You should get the same, or very close, reading as the power wire test. Anything less then that and there is resistance on the ground wire causing your problem. If you read 0 volts, wiggle the lead wires. If the reading changes then you are reading "ghost voltage”. Reset the safety pin, making sure it is making god contact inside the connector and try again. If the reading continues to show ghost voltage then there is a break in the ground wire somewhere.
Now test the MAF signal power & ground wires. They are the tan/light blue (power) & light blue/red (ground) wire. Be careful here and don’t short these two wires together because they are directly connected to the PCM. Shorting them could fry your PCM. To avoid shorting, only back probe one wire at a time. A voltmeter or multi-meter set to volts will not cause a short through its leads.
Test the signal ground wire
You should read within 0.5 volts of battery voltage. So if battery voltage was 12.6, you should read between 12.1 & 12.6 volts. Anything less then that and there is resistance on the ground wire causing your problem. If you read 0 volts, wiggle the lead wires. If the reading changes then you are reading "ghost voltage”. Reset the safety pin and try again. I would be very surprised if your reading stays 0 volts here.
Test the signal power wire (this is where an oscilloscope comes in handy):
At idle you should get a reading around 1 volt with little fluctuation. Snap the throttle a couple times and make sure the voltage returns to around 1 volt at idle. Now slowly increase the throttle to 2.5k RPMs and back down to idle. The voltage should increase & decrease smoothly from around 1 volt to around 1.8 volts and back down. The exact values don’t matter a whole lot, what you want is the voltage to increase/decrease smoothly. If the voltage suddenly spikes/drops at any point through the RPM range then the sensor is bad and should be replaced.
Since the trouble code is for a low voltage fault, if the sensor is clean, you get around battery voltage on the red wire, and significantly less then 1 volt on the signal power wire then the sensor is bad and is causing your problem.
If all the above check out, follow the signal power & ground wires to the PCM and run the same tests on it to see if the problem is in the wire between the sensor and the PCM . It is very rare for the problem to be the PCM.
Resistance on a wire can be any number of things, including but not limited to corrosion on a wire/connector, a damaged wire/connector, a loose wire/connector. To find the resistance walk up that wire towards the battery until you find a point with the reading you expect. The resistance will be between the first point you get a good reading and the last point you got a bad reading. Avoid poking holes in wires as that just creates a spot for moisture to get in and corrode the wire from the inside out. Back probe connectors whenever possible. If you must poke a whole in a wire apply a little liquid electrical tape or clear nail polish to the whole to seal it up after your done.
Ghost voltage is a tech term. It means that there is a break in the circuit somewhere and the leads are therefor not connected by that circuit. Touch the leads together and wiggle them to make sure that the break is not in the leads or meter itself. The voltage should remain constant while the leads are touching, but fluctuate when they are not. This is normal. If the leads check out, then there is a break in the circuit somewhere resulting in the power & ground sides of the circuit are not connected anymore.
Good luck...
Does your CAI use a K&N style filter (that is oily)? If so, the oil may have gotten onto the MAF and caused this fault.
The CEL means that the sensor is sending a lower then expected signal back to the PCM. A volt-meter or multimeter set to volts is all you need to test the MAF to see if it is bad but an oscilloscope is much better. Either way, there should be 4 wires going into the MAF sensor. According to my ’98 electrical diagnostics manual, the red wire should be a constant 12 volts. The black wire should be ground. Here is a quick way to test the MAF.
- Key ON, Engine OFF
- Set your meter to as close to 12 volts DC as possible without going under
- touch the negative meter lead to the negative battery post
- touch the positive meter lead to the positive battery post
Remember this voltage (a.k.a. battery voltage). It should be between 12.4 & 12.8 volts. If not, charge the battery before continuing.
Test the power wire:
- take a small safety pin and back probe the red wire at the connector
- touch the negative meter lead to the negative battery post
- touch the positive meter lead to the safety pin
You should read within 0.5 volts of battery voltage. So if battery voltage was 12.6, you should read between 12.1 & 12.6 volts. Anything less then that and there is resistance on the power wire causing your problem. If you read 0 volts, wiggle the lead wires. If the reading changes then you are reading "ghost voltage”. Reset the safety pin, making sure it is making god contact inside the connector and try again. If the reading stays at 0 volts then there is a short to ground somewhere on the power wire. If the reading continues to show ghost voltage then there is a break in the power wire somewhere.
Test the ground wire:
- take a small safety pin and back probe the black wire at the connector
- touch the negative meter lead to the safety pin
- touch the positive meter lead to the positive battery post
You should get the same, or very close, reading as the power wire test. Anything less then that and there is resistance on the ground wire causing your problem. If you read 0 volts, wiggle the lead wires. If the reading changes then you are reading "ghost voltage”. Reset the safety pin, making sure it is making god contact inside the connector and try again. If the reading continues to show ghost voltage then there is a break in the ground wire somewhere.
Now test the MAF signal power & ground wires. They are the tan/light blue (power) & light blue/red (ground) wire. Be careful here and don’t short these two wires together because they are directly connected to the PCM. Shorting them could fry your PCM. To avoid shorting, only back probe one wire at a time. A voltmeter or multi-meter set to volts will not cause a short through its leads.
Test the signal ground wire
- take a small safety pin and back probe the light blue/red wire at the connector
- touch the negative meter lead to the safety pin
- touch the positive meter lead to the positive battery post
You should read within 0.5 volts of battery voltage. So if battery voltage was 12.6, you should read between 12.1 & 12.6 volts. Anything less then that and there is resistance on the ground wire causing your problem. If you read 0 volts, wiggle the lead wires. If the reading changes then you are reading "ghost voltage”. Reset the safety pin and try again. I would be very surprised if your reading stays 0 volts here.
Test the signal power wire (this is where an oscilloscope comes in handy):
- Turn the car on and let it get to normal operating temp
- take a small safety pin and back probe the tan/light blue wire at the connector
- touch the positive meter lead to the safety pin
- touch the negative meter lead to the negative battery post
At idle you should get a reading around 1 volt with little fluctuation. Snap the throttle a couple times and make sure the voltage returns to around 1 volt at idle. Now slowly increase the throttle to 2.5k RPMs and back down to idle. The voltage should increase & decrease smoothly from around 1 volt to around 1.8 volts and back down. The exact values don’t matter a whole lot, what you want is the voltage to increase/decrease smoothly. If the voltage suddenly spikes/drops at any point through the RPM range then the sensor is bad and should be replaced.
Since the trouble code is for a low voltage fault, if the sensor is clean, you get around battery voltage on the red wire, and significantly less then 1 volt on the signal power wire then the sensor is bad and is causing your problem.
If all the above check out, follow the signal power & ground wires to the PCM and run the same tests on it to see if the problem is in the wire between the sensor and the PCM . It is very rare for the problem to be the PCM.
Resistance on a wire can be any number of things, including but not limited to corrosion on a wire/connector, a damaged wire/connector, a loose wire/connector. To find the resistance walk up that wire towards the battery until you find a point with the reading you expect. The resistance will be between the first point you get a good reading and the last point you got a bad reading. Avoid poking holes in wires as that just creates a spot for moisture to get in and corrode the wire from the inside out. Back probe connectors whenever possible. If you must poke a whole in a wire apply a little liquid electrical tape or clear nail polish to the whole to seal it up after your done.
Ghost voltage is a tech term. It means that there is a break in the circuit somewhere and the leads are therefor not connected by that circuit. Touch the leads together and wiggle them to make sure that the break is not in the leads or meter itself. The voltage should remain constant while the leads are touching, but fluctuate when they are not. This is normal. If the leads check out, then there is a break in the circuit somewhere resulting in the power & ground sides of the circuit are not connected anymore.
Good luck...
Last edited by petrock; Dec 11, 2012 at 07:06 AM.
Thread Starter
Joined: Dec 2012
Posts: 10
Well, i just want to say thank you very much everyone. I got the multimeter and tested the wires and sure enough the signal power wire was giving me a low reading like 0.10. I purchased the new MAF sensor, installed it, and rechecked with OBD II and it found no codes. I must say, i thought the car ran good when i got it but now that this is fixed, it REALLY runs good. Thanks again and be blessed :-)
4th Gear Member
Joined: Nov 2006
Posts: 1,669
From: CA
Well, i just want to say thank you very much everyone. I got the multimeter and tested the wires and sure enough the signal power wire was giving me a low reading like 0.10. I purchased the new MAF sensor, installed it, and rechecked with OBD II and it found no codes. I must say, i thought the car ran good when i got it but now that this is fixed, it REALLY runs good. Thanks again and be blessed :-)
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