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How to read PCM sensor (MAF) voltages (chasing P0171/P0174)
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atkinsonde
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Location: Fairbanks, Alaska, USA I think

PostPosted: Fri Jul 04, 2008 3:17 pm    Post subject: How to read PCM sensor (MAF) voltages (chasing P0171/P0174) Reply with quote

Hi, Does anyone know how one can read the sensor voltages that are coming into the PCM? I have an 02 MPV shop manual that shows them always hooking up SST "Special Service Tool" 49 UN01 130, which from what I can see gives you a pad of numbered pins that is hooked up between the PCM and the wiring harness, that allows you to check voltages on a large number of the sensors to see if they are in range.

My particular interest is the MAF. I have a code reader with live display that shows it at ~11 g/s for 2500 rpm, which is a little low (manual indicates between 12-15). I was wanting to double check MAF functioning using its output voltage.

This is all ultimately in pursuit of the P0171 and P0174... MAF has been cleaned so I'm moving on to vacuum lines, and the whistling noise that develops after the vehicle is warmed up.

Thanks for any help...

02 MPV LX - Green Diamond Icelander tires, block heater, tranny heater, oil pan heater, permanently mounted trickle charger - it'll start at -45 F/C and stop/start on black ice no problemo. Moonlights as a zambonie tower.

oh also have a delightful, tough 86 Subaru GL Sedan
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pweiss
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PostPosted: Fri Jul 04, 2008 6:23 pm    Post subject: Re: How to read PCM sensor (MAF) voltages (chasing P0171/P01 Reply with quote

My 2004 MPV has a mass airflow sensor with three pins in the connector.

The pin on one end is the battery voltage, the one on the other end is ground, and the one in the middle is the MAF readback voltage. If it is below 0.24V you will get a code P0102, and if it is above 4.8V you will get code P0103. On my 2004 MPV, the battery voltage to the MAF comes from main relay terminal D. The output voltage is connected to pin 88 of the PCM, and the ground pin connects to pin 36 of the PCM.

On a side note, my 2001 Nissan Maxima had code P0171 two weeks ago, and replacing the mass air flow sensor took care of the problem. Also, last week my MPV had code P0102, and the dealer replaced the mass air flow sensor and PCV hose under warranty to fix that problem.

I hope this helps; the information comes from my 2004 MPV shop manual.
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atkinsonde
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Location: Fairbanks, Alaska, USA I think

PostPosted: Fri Jul 04, 2008 8:33 pm    Post subject: Re: How to read PCM sensor (MAF) voltages (chasing P0171/P01 Reply with quote

Thanks for the help, pweiss. I'll have another look and see where I can get. My suspicions range beyond the MAF because I think that whistling noise is pretty indicative of something else triggering the codes.
02 MPV LX - Green Diamond Icelander tires, block heater, tranny heater, oil pan heater, permanently mounted trickle charger - it'll start at -45 F/C and stop/start on black ice no problemo. Moonlights as a zambonie tower.

oh also have a delightful, tough 86 Subaru GL Sedan
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mpvinnig
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PostPosted: Fri Apr 01, 2016 4:02 pm    Post subject: Re: How to read PCM sensor (MAF) voltages (chasing P0171/P01 Reply with quote

atkinsonde wrote:
Thanks for the help, pweiss. I'll have another look and see where I can get. My suspicions range beyond the MAF because I think that whistling noise is pretty indicative of something else triggering the codes.


vacuum leak, intake manifold gasket is key culprit

Am happy to announce that I have finally overcome the P0171/P0174 issue.

I have read and commented on nearly all the threads on this issue on this forum.

While there are many solutions, the key problem is a vacuum leak anywhere along the air intake and intake manifold channels.

Mine was solved my sorting out the intake gaskets!
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thzpcs
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PostPosted: Tue Apr 26, 2016 2:03 am    Post subject: Re: How to read PCM sensor (MAF) voltages (chasing P0171/P01 Reply with quote

pweiss wrote:
My 2004 MPV has a mass airflow sensor with three pins in the connector.

The pin on one end is the battery voltage, the one on the other end is ground, and the one in the middle is the MAF readback voltage. If it is below 0.24V you will get a code P0102, and if it is above 4.8V you will get code P0103. On my 2004 MPV, the battery voltage to the MAF comes from main relay terminal D. The output voltage is connected to pin 88 of the PCM, and the ground pin connects to pin 36 of the PCM.

On a side note, my 2001 Nissan Maxima had code P0171 two weeks ago, and replacing the mass air flow sensor took care of the problem. Also, last week my MPV had code P0102, and the dealer replaced the mass air flow sensor and PCV hose under warranty to fix that problem.

I hope this helps; the information comes from my 2004 MPV shop manual.


What do these voltages correspond to?
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mpvinnig
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PostPosted: Tue May 10, 2016 2:36 pm    Post subject: Re: How to read (MAF) voltages (chasing P0171/P0174) Reply with quote

For some reason, Ford vehicles have had a history of MAF sensor problems caused by contamination. In some cases, dirt gets past a leaky air filter and fouls the sensor wire. In other cases, carbon varnish builds up on the sensor from fuel vapors backing up through the intake manifold. Either way, contamination makes the MAF sensor sluggish, and often sets a P0171 or P0174 lean code.

The fix is to clean the sensor element with aerosol electronics cleaner (CRC makes a good product for this). The MAF sensor is located inside the air filter housing on some applications (Windstar, for example) or between the air filter and throttle body. Spray the sensor element with electronics cleaner, let it soak for about 10 minutes, then repeat. DO NOT use any other type of cleaner as this may damage the sensor. Also, DO NOT touch, scrub or attempt to physically clean the sensor element as this too can ruin the sensor.

http://www.aa1car.com/library/maf_sensors.htm

HOW TRUE!

I replaced my MAF Sensor and P0171/P0174 that i thought came from opening the intake manifold has gone and my LTFT is now very close to zero, which has not happened in a long while.


Last edited by mpvinnig on Tue May 10, 2016 3:00 pm; edited 2 times in total
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mpvinnig
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PostPosted: Tue May 10, 2016 2:38 pm    Post subject: Re: How to read (MAF) voltages (chasing P0171/P0174) Reply with quote

A bad mass air flow sensor in a vehicle makes starting difficult and affects the performance of the engine because he engine-control unit uses data from the MAF sensor to balance the fuel ratio the injectors deliver to the engine. A bad sensor returns a significantly different temperature than that of the engine coolant when read using a scan tool set to temperature.

The MAF sensor uses the temperature difference between the coolant and air entering the fuel mix to determine airflow. Under normal circumstances, the temperature of the air is a few degrees cooler than the coolant. If the sensor is bad and displays a temperature higher than the coolant level, the engine-control unit reduces the fuel flow, resulting in a lean operating condition that decreases fuel economy. If the temperature is reading too low, the unit sends too much gasoline, causing a rich operating condition, which also decreases economy.

Sometimes MAF sensors return bad temperatures due to an accumulation of dirt around the sensor. Cleaning the unit involves soaking it in rubbing alcohol in a plastic zipper bag. After cleaning, the unit requires about 20 minutes to dry before reinstallation. Most automobile parts stores carry cleaning kits for these sensors. When cleaning the units, owners should be cautious of the leads, which cannot be repaired if broken, necessitating replacement of the unit.

http://www.ask.com/vehicles/symptoms-bad-mass-air-flow-sensor-92d08b4e43f485b3
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