What are the symptons of a malfunctioning mass airflow sensor?
2002 Chevy 1500 series pickup
- K RLv 41 decade agoFavorite Answer
An engine with a bad MAF sensor may be hard to start or stall after starting. It may hesitate under load, surge, idle rough or run excessively rich or lean. The engine may
also hiccup when the throttle suddenly changes position.
If you suspect a MAF sensor problem, scan for any fault codes. A MAF problem should (but does not always) set a fault code. Codes that may indicate a problem with
the sensor include: GM: Code 33 (too high frequency) and Code 34 (too low frequency) on engines with multiport fuel injection only, and Code 36 on 5.0L and 5.7L engines that use the Bosch hot-wire MAF, if the burn-off cycle after shut-down fails to occur.
Of course, don’t overlook the basics, such as low engine compression, low vacuum, low fuel pressure, leaky or dirty injectors, ignition misfire, excessive backpressure (plugged converter), etc., since problems in any of these areas can produce similar driveability symptoms.
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 sensor’s 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 sensor’s 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 backprobing the brown-andwhite output wire to terminal B6 on the PCM. The voltage reading should be around 2.5 volts. If out of range, or if the sensor’s 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, it’s time for a new sensor.
On GM hot-film MAFs, you can also use a scan tool to read the sensor’s output in “grams per second” (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 won’t be able to deliver the right air/fuel mixture and driveability and emissions will suffer. So you should also check the ensor’soutput at various speeds to see that its output hanges appropriately. Another way to observe the sensor’s
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. Yet another way to check the MAF sensor is to see what effect it has on injector timing. Using an oscilloscope or multimeter that reads milliseconds, connect the test probe to any injector ground terminal (one injector terminal is the supply voltage and the other is the ground circuit to the computer that controls injector timing). Then look at the duration of the injector pulses at idle (or while cranking the engine if the engine won’t
start). Injector timing varies depending on the application, but if the mass air flow sensor is not producing a signal, injector timing will be about four times longer than normal (possibly making the fuel mixture too rich to start). You can also use millisecond readings to confirm fuel enrichment when the throttle is opened during acceleration, fuel leaning during light load cruising and injector shut-down during deceleration. Under light load cruise, for example, you should see about 2.5 to 2.8 Ms duration.
- MaryLv 44 years ago
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I agree with other answer that there are several symptoms such as poor idle, stalls, or no starts. If the sensor is bad or contaminated bad enough, there is usually a check engine light illuminated. If the sensor is contaminated, I often see vehicles crank and then stall; similar to faulty idle air control valves. Unlike the idle air valves, if the hold the throttle partially open, the vehicle will still stall. I've seen dirt from bad air filters, bugs, and oil from K&N air filters all contaminate the MAF. If the MAF is faulty and creating a no start or start and stall condition, the vehicle should run with the sensor disconnected. The PCM does this as a fail safe. If the sensor is bias, your vehicle may run rich (too much fuel) or lean (not enough fuel) because the MAF is the PCM's primary input for calculating the proper air fuel ratio.
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- Anonymous5 years ago
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What are the symptons of a malfunctioning mass airflow sensor?
2002 Chevy 1500 series pickupSource(s): symptons malfunctioning mass airflow sensor: https://tr.im/qeeBx
- Charles CLv 51 decade ago
I agree with KR above. The tools may not be available though.
The most basic test is to unplug the MAF while the engine is turned off, and then start it. Most of the time it will run better without it if the sensor has failed. This is because the computer can do a better job of assuming what's going on if it is not receiving a misleading signal. The case where this test will produce invalid results is if the MAF is completely dead or not sending any signal at all.
- 5 years ago
I believe the mass sensor on my chevy 2500 is bad. It does feel like the engine is choking or straining off the line. Most notable is a LOW sublime idle. I did have problems starting the truck a few times...
- 5 years ago
The first answer is proper and accurate!!! I am wanting to share what happened on my 2002 ford f150 pickup just to share with others what these maf sensors can cause. It would idle up and down and then in gear would be okay until I accelerated then would stall and die or suddenly lurge the vehicle forward which could cause a wreck like one man in here described happened to his wifes car. Amazing a maf can cause all of this nightmare. Any sensor on vehicles than cause cause a car to go crazy in traffic should be removed by the manufacturer and made to be as pre maf autos that ran without them. My 98 dodge ram doesn t even have a maf sensor and it runs great
- 5 years ago
The MAF on my 3.8L OLDS almost caused a car accident. It caused my unsuspecting wife to almost hit a car in front of her but she had the mind set to turn onto the curb. It did set a code error after that incident. The MAF called for an increase in fuel when the engine stumbled and almost died at idle. If the brake is not being applied at the time the engine surges for only a second but that is enough to send the car suddenly forward and could be catastrophic if in close proximity to something or someone.
Readings using the OBD II scan tool before the error was picked up showed MAF g/s at 5.73 with RPM at 846 RPM. After error code P0102 it showed MAF g/s at 1.75 at 2171 RPM. With new MAF replacement it showed MAF g/s @ 18.77 at 1432 RPM. Tapping on the MAF did nothing for causing engine stumble. You can see that the new MAF has much higher airflow at a lower RPM, which you can use to check your MAF. I don’t want anyone else to experience what my wife did.
- 1 decade ago
the car will feel like its choking
- 3 years ago
where are maf relays