MAF Sensor voltage issue 2004 Montero Limited

[jasonsuperb]

Sorry to cross post been trying to figure this out in my build thread but haven't gotten any replies there, figure not many people see it.

Ive been having an issue with my Montero where it won't idle. It threw a MAF low voltage code P0102.

After replacing the air filter and cleaning the MAF it still wouldn't idle, just rev to 1200 and drop to 300, back and forth, and smell like gas, it would act as if the MAF was disconnected. MAF sensor on the scanner reads 0. I got a multi meter and checked the power wire to the MAF and only saw around 6 volts. From what I read online I should see between 10-13 Volts. I decided to charge the Battery and after giving it a full charge, it started up and idled normally, I drove it to work and back no issues. Then a few days later its back to not idling. I check the voltage at the MAF again back at 6V check the battery voltage 12.3 I put it back on the charger, get it back to full charge and check the volts at the MAF again 8.5 Volts, start it up and its running again.

So I can't figure out why the car has enough battery to start the car but not enough battery to run the MAF?

Is there any reason why the voltage at the MAF would be lower than the battery? I should note I put in a brand new battery and terminals in the process to make sure that wasn't the issue.

Thanks for any insight!

 

[jasonsuperb]

Well I was testing some more, it is running now after fully charging battery and I realized that the bolt I was using on the chassis to use as a ground for my test must not have been ideal, when I test the voltage at the MAF now using the negative terminal on the battery I get 12.5 volts. I don't know however what that voltage would have been before I charged the battery when the engine wouldn't run and was throwing codes. Still the bizarre thing is the battery had enough charge to start the car but somehow not enough for the MAF to work, then after charging the Battery fully it works...for now. Any reason why that would happen? I know its gonna happen again and strand me somewhere.

 

[jasonsuperb]

Another thing I noticed while running these tests is the fan is running all the time, even when I start the engine when its cold it starts up immediately and never shuts off until I turn the engine off, not sure if this is possibly related

 

[Salonika]

I’m not familiar with your vehicle or your situation, but remember the positive feed to your starter is a direct line from the battery whereas positive to your MAF comes from the computer, which gets juice from a relay, through a fuse block, etc., back to battery positive. This might explain how it could happen, but I suspect something else is up.....if the MAF wasn’t getting adequate juice because of battery, then other things would also be affected, right?

 

[haolepinoy]

What is your battery voltage with the car running?

 

[Salonika]

Most automotive sensors do not operate at 12v (none I can think of), the computer regulates sensor operating voltages......if they did then a car with a low battery would not run......cars will still run even if you don’t have enough juice to start them and a failed alternator. Think of push starting a manual with « dead » battery and failed alternator. You can drive for a while until you get really low on the battery to the point where it starts to affect spark and sensors. From my experience most automotive sensors input voltage is 5-6 volts max.

 

[haolepinoy]

Most automotive sensors do not operate at 12v (none I can think of), the computer regulates sensor operating voltages......if they did then a car with a low battery would not run......cars will still run even if you don’t have enough juice to start them and a failed alternator. Think of push starting a manual with « dead » battery and failed alternator. You can drive for a while until you get really low on the battery to the point where it starts to affect spark and sensors.

This is exactly where I was going with this. I smell an alternator problem.

 

[Salonika]

I’m confused though since he said he was measuring 12v at the sensor.....I’d have to check the FSM to see if the harness is supposed to deliver 12v to the MAF. I don’t think that is the case generally, but I’d have to check.

 

[haolepinoy]

Here's a mashup of FSM data I put together on the Volume Air Flow Sensor (the MAF) that explains how it works voltage wise:

Volume Airflow Sensor

DTC P0101: Volume Airflow Circuit Range/Performance Problem [FSM 13Ac-2 thru 8]

DTC P0102: Volume Airflow Circuit Low Input [FSM 13Ac-9 thru 17]

Circuit Operation

• The volume airflow sensor power is supplied from the MFI relay (terminal No. 1), and the ground is provided on the PCM (terminal No. 88).
• 5-volt power is applied to the volume airflow sensor output terminal (terminal No. 3) from the PCM (terminal No. 63). The volume airflow sensor generates a pulse signal when the output terminal and ground are opened/closed (opened/short).

Technical Description

• While the engine is running, the volume airflow sensor outputs a pulse signal which corresponds to the volume of air flow.
• The PCM checks whether the frequency of this signal output by the volume airflow sensor while the engine is running is at or above the set value.
• When the throttle position sensor output voltage is low, the PCM causes the power transistor to be "ON" to send an volume airflow sensor reset signal to the volume airflow sensor. In response to the reset signal, the volume airflow sensor resets the filter circuit and improves the ability of the volume airflow sensor to measure the amount of air in a small air intake region.

Connector B-48 Pins

1. Barometric Pressure Sensor Supply Voltage
2. Barometric Pressure Sensor Output Voltage
3. Volume Airflow Sensor Output Voltage
4. Volume Airflow Sensor Supply Voltage
5. Ground
6. Air Intake Sensor Supply Voltage
7. Volume Airflow Sensor Signal Reset

 

[haolepinoy]

This table doesn't translate over well format wise, but this is how to test and interpret the values you get from testing the B-48 connector.

Parameter.....Test Conditions.....Standard Values
Live Data.....Engine On, Warmed Up, Idling.....10 Hz. at idle, increasing with engine speed.

B-48 #3 Sensor Supply Voltage.....B-48 Disconnected, Ignition On, Harness Side to Ground.....4.8 - 5.2v

B-48 #4 Power Supply Voltage.....Ignition On, Backprobe to Ground.....Battery + Voltage

B-48 #5 Continuity Check.....B-48 Disconnected, Ignition Off, Harness Side to Ground.....< 2.0 ohms

B-48 #7 Reset Signal Voltage.....1) Ignition On, Backprobe to Ground; 2) Engine On, Warmed Up, Idling, Backprobe to Ground.....1) 6.0 - 9.0v; 2) < 1.0v at idle, 6.0 - 9.0v at > 3,000 rpm

 

[haolepinoy]

I’m confused though since he said he was measuring 12v at the sensor.....I’d have to check the FSM to see if the harness is supposed to deliver 12v to the MAF. I don’t think that is the case generally, but I’d have to check.

I'm not sure either, unless he is backprobing the #4 pin on the connector, but that should read the same as the battery voltage at the positive terminal. If he's only seeing 12.5 volts he's got a bad alternator. That's why I asked what the voltage was at the battery with the car running.

Regarding the OP's readings of 6 and 8.5 volts mentioned earlier...we need more info on how he's testing (which pin?, backprobing or disconnected?, engine running or just ignition on?, open or closed loop idle?) to figure out what's going on. Those voltages could be completely normal depending on which pin is being tested. They're likely just signal voltage that are supposed to change with air flow volume.

 

[jasonsuperb]

What is your battery voltage with the car running?

Just checked this and got 14.4 volts so it appears the alternator is functioning.


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[haolepinoy]

Just checked this and got 14.4 volts so it appears the alternator is functioning.


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Good. I'd keep an eye on it, just to make sure that it doesn't randomly drop voltage while driving...maybe a bad ground or loose terminal or worst case, a failing voltage regulator that's in an out (due to an oil leak...common issue). Unfortunately our Gen3's do not come with a voltage meter in the dash, but since you have a scanner you could monitor it with that. I have a little plug voltmeter that I used to leave in the 12v outlet by the ashtray. I've since gotten an Ultra-gauge. Either or anything like that will help. You'll see @ 14.4v at startup with the system dropping back down to @ 13.8 once the battery has been topped up. Under heavy load the voltage can drop down further, but if you're seeing anything south of 12.7v (with the engine running) you've got a problem.

If you want to press in on your MAF, here's the places to look for testing it: FSM 13Ac-2 thru 17. If you need a copy of the FSM I think you can still find a copy on mitsubishilinks.com or .net (can't remember the exact hyperlink....ask Normal Dave, it's his site I think). Those pages will walk you through how to test the signal and supply voltages under different circumstances to determine if you have a problem with either the sensor, the connector, a wire, or (God-forbid) the PCM. If you're testing your MAF with a OBD-II scanner you shouldn't be seeing voltage, but rather some sort of frequency reading since our MAFs are Karmen Vortex units. But you can backprobe at the connector with a multimeter on the different pins in order to interpret the voltages there (all spelled out in the FSM).

Another thing to note is that if your MAF does fail, the PCM will revert to a fixed map in order to stay running. A dead (or disconnected) MAF will not normally cause your engine to die on a Gen3. It will just cause it to regulate fuel trims based on predetermined data rather than real time inputs from your sensor.

I hope yours is easy to figure out. These things are a real pain once they start getting wonky. It's hard to diagnose right without diving in head first. And they are very often misdiagnosed, with people slinging expensive parts at them. These electrical gremlins...

 

[jasonsuperb]

I was testing the connector with it disconnected and with the key turned to on but the car not running. I was testing connector 4 from the picture attached to see if it was getting power because the car was acting the same with the connector connected and disconnected. It will basically not run, it will rev then drop and if you give it gas it will stall. At the moment it is running normally, but ever since I have had it (about 1 month now) it gets horrible gas mileage, about 13-14 mpg, which is mostly highway. I tested the battery for parasitic loss and found about -2 amps. I disconnected what I think was the dome light fuse and it dropped down to about .05 amps. however with that fuse out the stereo, display above stereo, dome lights, and power locks stopped working as well, maybe other things I didn't even notice, so I am not exactly sure what on that fuse is causing the loss, and if it is related to the main issue I'm having.

No one mentioned anything about the fact that the fan runs the whole time the car is on, does anyone think that could be related or a separate issue?

I accidentally fried my multimeter by forgetting to put it back to volts after checking amps so I need to get another one before I can do more diagnostics.

 

[Salonika]

No one mentioned anything about the fact that the fan runs the whole time the car is on, does anyone think that could be related or a separate issue?

I accidentally fried my multimeter by forgetting to put it back to volts after checking amps so I need to get another one before I can do more diagnostics.[/QUOTE]
On that fan.....this is just a guess, but given idle issues, gas smell (mixture off?), and the fan running....maybe coolant temp sensor? I’m surprised that out of all this, you are only getting a trouble code for the MAF. The procedure for checking coolant temp sensor is pretty basic with a meter.