How to: MAF Sensor Test Procedure

[2000StreetRod]

Background

A nonfunctional mass air flow (MAF) sensor can significantly degrade engine performance. The PCM utilizes the MAF sensor output voltage to determine engine load which is used to adjust the air/fuel ratio during acceleration. The typical engine performance symptoms caused by a dirty or defective MAF sensor are lack of power and hesitation during acceleration. The MAF sensor element wires become dirty with age and become contaminated from excessively oiled air filters. Cleaning the element with MAF sensor cleaner should be performed frequently and often will cure MAF related engine performance issues.

Testing

With the MAF sensor electrical connector connected backprobe the sensor signal (light blue/red wire) and the sensor return (tan/light blue wire) at the connector.

Connect the positive lead of a voltmeter to the sensor signal and the negative lead to the return.

With the parking brake set and the gear selector in Park start the engine.

Monitor the MAF sensor output voltage while increasing engine speed. The voltage should increase smoothly with no dropouts as the engine speed increases. Listed below are representative values.

RPM Voltage
550 0.8
1000 1.0
1500 1.25
2000 1.4
2500 1.55
3000 1.65
3500 1.9
4000 2.1

 

[flyingpootang]

2000StreetRod, Excellent thread. I've look high and low on the net and couldn't find this info anywhere. Unfortunately my MAF is reading perfectly so my search goes on....

 

[jperez09]

2000StreetRod, Excellent thread. I've look high and low on the net and couldn't find this info anywhere. Unfortunately my MAF is reading perfectly so my search goes on....

@flyingpootang

is your engine misfiring maybe?? buy new plugs and a coil pack.

 

[flyingpootang]

JP, My 5R55w tranny has the common up shift slip and bang into reverse syndrome. I pulled the Int and OD servos and the bore are perfect, the fluid was dark w/ no metal, and all the shift solenoids all ohmed out perfectly. The Sonnax Alphabet stated to check all the grounds and clean the MAF. The reason I suspected the MAF is the problem happens in open loop and I was alos having problems with the truck idling in open loop w/o staying on the gas pedal. Once in closed loop it idled perfectly...

 

[drakesis]

How do I test a MAF if the truck only runs when the MAF is unplugged???

 

[2000StreetRod]

Engine not running MAF sensor test

If your engine runs better with the MAF sensor disconnected that is a fairly good indication the sensor is bad. The PCM is reverting to stored parameters and ignoring what it thinks is bad data from the MAF sensor. Are you using a stock MAF sensor or have you installed a non-standard one?

You can perform some voltage measurements with the ignition On and the engine not running. With the MAF sensor connector disconnected you should read battery voltage between the B+ and PWR GND pins on the connector. As I recall with the MAF sensor connected you should read 0.5 to 1.0 volts between the back probed SIG and GND pins. I suspect the SIG to GND reading will be either almost 0.0 volts or greater than 5.0 volts and that is why the PCM is ignoring the out of range value.

 

[drakesis]

I replaced it with another stock one (same serial ID), and still nada unless the 2nd MAF was junk (from the junkyard) to start with....?

I am getting battery voltage on the Red wire & ground, I'll have to check again for the SIG.

 

[drakesis]

I got from the SIG to GND 0.04volts, so I'll take it back and see if I can get another one..... Hopefully it will be a good one...

 

[drakesis]

I still get 0.04volts with another MAF

 

[gmanpaint]

I have a question about aftermarket MAF sensors and housings.
Does anyone know if there is a 70mm MAF set up for a 2nd gen conical style intake tube and an OVAL plug on the sensor?

I have tried to communicate with a couple places with no luck on any info. Summit has stopped selling the MAF for some reason, I have the new catalog, and have checked the site, Nadda.


Sorry for the thread jack.
Carry on

 

[2000StreetRod]

Backprobing?

I still get 0.04volts with another MAF

Are you measuring with the ignition On, electrical connector connected to the MAF sensor and backprobing the pins? Are you backprobing the light blue/red (SIG) wire/pin and the tan/light blue (GND) wire/pin?

 

[drakesis]

Are you measuring with the ignition On, electrical connector connected to the MAF sensor and backprobing the pins? Are you backprobing the light blue/red (SIG) wire/pin and the tan/light blue (GND) wire/pin?

Yes, I have.... I even replaced the old wires with new ones straight to the PCM and it still hasn't solved my problem.... I've been pulling hair outta my head all week....

 

[2000StreetRod]

Test the returns

Yes, I have.... I even replaced the old wires with new ones straight to the PCM and it still hasn't solved my problem.... I've been pulling hair outta my head all week....

I suggest that you disconnect the electrical connector to the MAF sensor and measure the resistance (ignition Off) from the black wire pin (PWR GND) to chassis ground. It should be a short.

 

[drakesis]

I suggest that you disconnect the electrical connector to the MAF sensor and measure the resistance (ignition Off) from the black wire pin (PWR GND) to chassis ground. It should be a short.

StreetRod, I just went out and check the Black (PWR GND). I hooked the DVOM red lead to the Black (PWR GND) and to the closest ground on the body. I got 0.00, DVOM was set to 20K...

I check continuity with the buzzer it buzzzzzzzzzz.....

Exact same results when I test the Black (PWR GND) to the negative terminal on the battery.

The ignition was off the entire time.

 

[2000StreetRod]

Running out of ideas

In the past I have simulated my MAF sensor with a variable voltage supply connected between the SIG wire and the SIG GND wire. As I recall the engine would start and run with no DTC when the voltage was between 0.5 and 1.0 volts. For some reason you have only 0.04 volts. If the power to your PCM was bad then the engine would not start and run. It is unlikely that the 3 MAF sensors (original plus two salvage yard replacements) are all totally bad. Maybe the connection to your PCM is bad. Have you tried disconnecting and reconnecting the PCM main connector? Is the bolt that holds the PCM connector snug (but not too tight) in place? Maybe your MAF sensor connector is bad and not mating correctly with the MAF sensor pins.

 

[drakesis]

In the past I have simulated my MAF sensor with a variable voltage supply connected between the SIG wire and the SIG GND wire. As I recall the engine would start and run with no DTC when the voltage was between 0.5 and 1.0 volts. For some reason you have only 0.04 volts. If the power to your PCM was bad then the engine would not start and run. It is unlikely that the 3 MAF sensors (original plus two salvage yard replacements) are all totally bad. Maybe the connection to your PCM is bad. Have you tried disconnecting and reconnecting the PCM main connector? Is the bolt that holds the PCM connector snug (but not too tight) in place? Maybe your MAF sensor connector is bad and not mating correctly with the MAF sensor pins.

I did remove the PCM connector, to test continuity for the SIG & SIG GND, What I found was that the female pin was pushed far back away inside the connector. That was only for the BL/R wire, I tried getting it to stay flush like the rest of the pins, but not sure if it really worked. It kept wanting to slide back, I can particularly pull that wire right out of the connector. I tried putting a paperclip in the back side of the connector to push the female pin into the PCM, it still didn't do a different. But I'm not sure if it really make them make contact......?

 

[2000StreetRod]

Potential problem source

I did remove the PCM connector, to test continuity for the SIG & SIG GND, What I found was that the female pin was pushed far back away inside the connector. That was only for the BL/R wire, I tried getting it to stay flush like the rest of the pins, but not sure if it really worked. It kept wanting to slide back, I can particularly pull that wire right out of the connector. I tried putting a paperclip in the back side of the connector to push the female pin into the PCM, it still didn't do a different. But I'm not sure if it really make them make contact......?

If that pin is not making contact that might be the source of your problem. I'm not familiar with the PCM connector. Normally an extraction tool is required to remove the pin with wire from the housing. If it is easy to pull the wire/pin from the housing then the retaining mechanism is damaged. You may be able to spread the collar with a very small screwdriver enough for it to lock in place when inserted into the housing.

 

[drakesis]

If that pin is not making contact that might be the source of your problem. I'm not familiar with the PCM connector. Normally an extraction tool is required to remove the pin with wire from the housing. If it is easy to pull the wire/pin from the housing then the retaining mechanism is damaged. You may be able to spread the collar with a very small screwdriver enough for it to lock in place when inserted into the housing.

I haven't had the chance to go back out and try the pin again.... I was looking at my notes I wrote when doing various tests...

The CEL gave a code but only from the Continuous Memory and not live.
Both codeds were 122 and 157, my book tells me "low voltage or input" for MAF & TPS. I had check the TPS with ignition on and I got proper voltage when I moved the throttle between 0.5v to 5v. That tells me it's working fine, correct? Or maybe not?

If a ground is shorted on the TPS would it cause problems with the MAF? I'm going to check the ground again on the TPS...

 

[2000StreetRod]

CEL for MAF sensor not TPS

. . . The CEL gave a code but only from the Continuous Memory and not live.
Both codeds were 122 and 157, my book tells me "low voltage or input" for MAF & TPS. I had check the TPS with ignition on and I got proper voltage when I moved the throttle between 0.5v to 5v. That tells me it's working fine, correct? Or maybe not?

If a ground is shorted on the TPS would it cause problems with the MAF? I'm going to check the ground again on the TPS...

The PCM checks the TPS and the MAF sensor for outputs in the correct range. Your TPS readings sound normal so the code was probably for the MAF sensor. The return for the TPS is not common with the return for the MAF sensor. The TPS return is common with some other returns but is not connected to chassis ground.

 

[Doc Hvac]

street rod........thank you........i changed my bad maf with a good clean used one from a salvage yard. i still had prob's i just checked my maf 0.9 at idle 2.1 at 2000 rmps and i was getting a 186 code. changed with new one going to see how it works................