MAF sensor Bad?

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  #1  
Old 05-10-04, 10:24 AM
colmac
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MAF sensor Bad?

I am geting a P0101 which means Mass Air Flow circuit/performace problem. I removed the sensor and cleaned it. All was fine for a few days then the check engine light came on again. Any ideas how to test this sensor. The price of a new one is 192.00 dollars. Btw, I had a K&N cleaner in. But after reading that the oil may be causing the sensor to fail I replaced it with an OEM filter cleaned the sensor and still the MIL comes on. Please post any ideas you may have, thanks in advance -cm
oh and the truck is a 2500HD 8.1L Gas
 

Last edited by colmac; 05-10-04 at 10:29 AM. Reason: need more detail
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Old 05-10-04, 02:42 PM
WeldGod's Avatar
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Maf

There are quite a few potential problems as well as ways to test the MAF. What year is the truck? I am not sure of the current MAF sensors used today. Injector timing should always vary, if your MAF is sending a signal. If your MAF is not sending a signal the pulses to the injector will about 5 times longer than they should be. With a multi-meter (that reads milliseconds) or oscilloscope, test the current time for an injector, just as a basic guide under a normal cursing speed (RPMS) you should see about 2.7ms length.
 
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Old 05-11-04, 04:10 AM
colmac
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2002 2500HD 8.1L gas

It is a 2002 2500HD with 8.1L gas. The MAF is just off the air box. It has about 4 small wire wound resisters/thermisters. The truck runs fine. If I clear the codes they come back in a few days. The sensor "looks" fine. Here is the freeze frame when the last time this occurred. I am not sure how to read this data or if it is giving any clues to the problem.

FREEZE FRAME DATA: Trouble Code which triggered Freeze Frame P0101
FREEZE FRAME DATA: Fuel System Feedback Status CLOSED LOOP
CLOSED LOOP
FREEZE FRAME DATA: Calculated Engine Load, % 57.7
FREEZE FRAME DATA: Coolant Temperature 196
FREEZE FRAME DATA: Short Term Fuel Trim % (Bank 1) -0.8
FREEZE FRAME DATA: Long Term Fuel Trim % (Bank 1) 5.5
FREEZE FRAME DATA: Short Fuel Trim % (Bank 2) -2.4
FREEZE FRAME DATA: Long Term Fuel Trim % (Bank 2) -0.8
FREEZE FRAME DATA: Intake Manifold Pressure 25.4
FREEZE FRAME DATA: Engine Speed RPM 3736
FREEZE FRAME DATA: Vehicle Speed 54

As I stated before everything runs fine and seems to get the same gas milage.

Is there a voltage test? Like at idle what should the voltage on the sensor be vs at a higher RPM.

Is there a total resistance test across the sensor?

Thanks for any help/information
-colin
 
  #4  
Old 05-11-04, 09:05 AM
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This should give you quite a few tests. I hope you find the sanswer your are looking for.

TESTING
MAF sensors can be tested either on or off
the vehicle in a variety of ways.
You can use a MAF Sensor Tester and
tachometer to check the sensorís response.
If testing on the vehicle, unplug the wiring
harness connector from the sensor and
connect the tester and tachometer. Start the
engine and watch the readings. They should
change as the throttle is opened and
closed. No change would indicate a
bad sensor. The same hookup can be
used to test the MAF sensor off the
vehicle. When you blow through the sensor,
the readings should change if the sensor is
detecting the change in air flow.
Another check is to read the sensorís voltage
or frequency output on the vehicle. With
Bosch hot-wire MAF sensors, the output
voltage can be read directly with a digital
voltmeter by back probing the brown-and white
output wire to terminal B6 on the
PCM. The voltage reading should be around
2.5 volts. If out of range, or if the sensorís
voltage output fails to increase when the
throttle is opened with the engine running,
the sensor may be defective. Check the orange
and black feed wire for 12 volts, and the
black wire for a good ground. Power to the
MAF sensor is provided through a pair of
relays (one for power, one for the burn-off
cleaning cycle), so check the relays too, if the
MAF sensor appears to be dead or sluggish.
If the sensor works but is slow to respond to
changes in air flow, the problem may be a
contaminated sensing element caused by a
failure in the self-cleaning circuit or relay.
With GM Delco MAF sensors, attach a
digital voltmeter to the appropriate MAF
sensor output terminal. With the engine
idling, the sensor should output a steady 2.5
volts. Tap lightly on the sensor and note the
meter reading. A good sensor should show
no change. If the meter reading jumps and/or
the engine momentarily misfires, the sensor
is bad and needs to be replaced. You can
also check for heat-related problems by
heating the sensor with a hair dryer and
repeating the test.
This same test can also be done using a
meter that reads frequency. The older AC
Delco MAF sensors (like a 2.8L V6) should
show a steady reading of 32 Hz at idle to
about 75 Hz at 3,500 rpm. The later model
units (like those on a 3800 V6 with the
Hitachi MAF sensor) should read about
2.9 kHz at idle and 5.0 kHz at 3,500 rpm.
If tapping on the MAF sensor produces a
sudden change in the frequency signal,
itís time for a new sensor.
On GM hot-film MAFs, you can also use
a scan tool to read the sensorís output in
ďgrams per secondĒ (gps), which corresponds
to frequency. The reading should go from
4 to 8 gps at idle up to 100 to 240 gps at
wide-open throttle.
Like throttle position sensors, there should
be smooth linear transition in sensor output
as engine speed and load change. If the
readings jump all over the place, the computer
wonít be able to deliver the right air/fuel
mixture and driveability and emissions will
suffer. So you should also check the sensorís
output at various speeds to see that its
output changes appropriately.
Another way to observe the sensorís
output is to look at its waveform on an
oscilloscope. The waveform should be square
and show a gradual increase in frequency as
engine speed and load increase. Any skips
or sudden jumps or excessive noise in the
pattern would tell you the sensor needs to
be replaced.





From:Wells Point Diagnosis and Drivability Resource
 
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