P0102 Mass Air Flow Low Frequency code with good MAF

Good afternoon,

I attached a flow chart for you to follow.

Follow the steps and let me know what you find.

Roy

Circuit Description

The Mass Air Flow (MAF) sensor measures the amount of air which passes through it into the engine during a given time. The PCM uses the mass air flow information to monitor engine operating conditions for fuel delivery calculations. A large quantity of air entering the engine indicates an acceleration or high load situation, while a small quantity of air indicates deceleration or idle.

The MAF sensor produces a frequency signal which can be monitored using a scan tool. The frequency will vary within a range of around 2000 Hertz at idle to near 10,000 Hertz at maximum engine load. DTC P0102 will be set if the signal from the MAF sensor is below the possible range of a normally operating MAF sensor.


Conditions for Setting the DTC

The engine is running.

MAF signal frequency is below 1200 Hertz.

Above conditions present for over 0.5 seconds.

Throttle angle below 75%.


Action Taken When the DTC Sets

The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the first trip in which the diagnostic test has been run and failed.

The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.


Conditions for Clearing the MIL/DTC

The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.

The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

The DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.


Diagnostic Aids

Check for the following conditions:

Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

Misrouted harness. Inspect the MAF sensor harness to ensure that it is not routed too close to high voltage wires such as spark plug leads.

Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving connectors and wiring harnesses related to the MAF sensor. A change in the display will indicate the location of the fault.

Plugged intake air duct or filter element. A wide open throttle acceleration from a stop should cause the Mass Air Flow displayed on a scan tool to increase from about 4-7 gm/s at idle to 100 gm/s or greater at the time of the 1-2 shift. If not, check for a restriction.

If DTC P0102 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set.

Test Description

The numbers below refer to the step numbers on the Diagnostic Table:

2. This step verifies that the problem is present at idle.

5. A voltage reading of less than 4 or over 6 volts at the MAF sensor signal circuit indicates a fault in the wiring or a poor connection.

6. Verifies that ignition feed voltage and a good ground are available at the MAF sensor.

13. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to PCM Replacement and Programming Procedures.

Thanks for the information, this is a long version of what I found on-line about testing the MAF in a GM 3.1.

I originally checked all plugs and connectors and insured they were clean and used dielectric grease when reattaching them. The plenums are clear and clean and the air-box has a new filter. I ran the test for the MAF, but I don't know what range the hertz signals should be, but as I stated, it was smooth and rose and fell with the throttle.

I have a Haynes manual arriving tonight and I hope like hell it helps, as replacing parts and taking it to shops for them to tell me what I already know is getting me no where. Quite frustrating.

With the knowledge I have given, what do you think my next step is?

Did you follow the flow chart and what were your results?

roy

I think I'm tracking with you on my Foxwell having a (g/s) reading for the MAF. It seems it was in the 4-5 during idle and was at the 40-50 range when it was bogging down, but when it cleared and accelerated as expected, it was well into the high 60's and into the 70's. Is this something that assists? Both the original GM MAF and the new replacement AC Delco MAF are performing the exact same way.

Did you replace the connector to the sensor? It is very common for the connector to be faulty.

If all that is good, then a good chance the ECM is the issue.

Roy

Interesting, I never thought the connector could be an issue. I did have the same exact issue with the new MAF sensor, and I got the clear ground, power and signal power at the wiring harness. How exactly would I check that outside of these checks.

Yes, the ECM is my next thought too. I could have the original ECM reprogrammed and/or I can have a replacement unit reprogrammed (I grabbed a $30.00 used ECM with the same model and serial numbers from a recycling yard that was in a 1997 Skylark last Saturday).

Thanks so much BTW, you've been awesome and invaluable!

Since I have an additional ECM, I'm thinking of downloading: http://www.mediafire.com/file/bc92by7ao7fp1la/GM_2000NAO.7z/file
and putting that Skylark ECM in the car and reprogramming it to the most recent GM default upgrade (or "flash" it as they say on line) as my daughter's Lumina VIN number and see if I can resolve the issue. All I understand that I need need is this free program, my computer and a OBDLink SX USB cable. This sound doable for a unpaid mechanic, haha?

I do not think that will work. You can try it but I doubt it.

Roy

If it does work please let us know.

Interesting... it seems like the issue is the CMU not issuing the correct indicators to the engine components based on the MAF info it's seemingly getting. Since I have the bonus CMU, I'll try it, but what do you think is the issue is it's not the MAF even though the code says it is? Quite frustrating I'll admit.

The ECM is not seeing the signal. All your readings look good but the ECM is not processing it so it is coding because it is not seeing it.

Sounds like you need an ECM.

Roy

Lets check the connection between the PCM and MAF. here is a guide and the wiring diagrams so you can see how the system works and which wires to check:

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (below). Please let us know what happens.

Thanks for the advice!

I did ohm out the yellow signal wire from the MAF harness to the PCM harness pin and I got no tone and about 1.87 on the resistance. I then ran a same gauge yellow wire along the existing plastic conduit (wire bundle cover) and skinned back the existing wire just short of each harness and wrapped the new wire for good contact. I then checked the connector to connector and had tone and something like .002. I then put everything back together and drove it.

She went up hills fine but there was a slight hesitation here and there, so I plugged in my Foxwell and saw the MAF (g/s) stayed steady at 1.95 no matter my acceleration. I then thought the old wire still in the circuit might be the issue, or the original MAF sensor that I put back on was bad (I thought not as the new MAF sensor threw the same readings, but it could have been the wire). So I returned home to cut out the old wire and see how she ran back to the auto parts store to get a new MAF.

I cut the old yellow sensor wire free at both ends and wrapped the ends good. Got it to start her and she wouldn't start.

She just spun the starter.

Foxwell was connected and stated there was no error code.

So I checked a few of the fuses, they were good. I'll need to start at fuel pressure, and so one to find out what happened between leaving the old sensor wire and taking it out.

Am I missing something simple???

Frustration sets in. I need a breather for an hour or so before I get back into it.

Thanks guys!

How did you check the resistance?

What tool were you using?

Roy

I use my BKPrecision Test Bench 388-HD.

I checked the wire/solder and it all shows connectivity, and I checked the other pins around the MAF sensor input wire at the lower large PCM plug in case my manipulation of the wires to get to the yellow MAF sensor wire caused any damage.

Another thought: although I always disconnected the battery hot before working with the PCM or other wiring (like soldering in a new sensor wire), I didn’t disconnect the positive side of the battery to disconnect the old sensor wire I theorized might be causing signal issues. I used insulated snips, and didn’t cut any other wires, but I’m wondering about anything that could have occurred.

Just to be clear, did you run the overlay wire without disconnecting the original wire?

Roy

Yes. Then, when it was better, but seemed a little hesitant, I theorized the original wire’s still attached and attempting to carry signal, so removing it from the carrying material might clean up the signal so the info is clearer for the PCM. Or so I thought.

I can’t help but think it’s something that got altered during the getting to and putting back of everything else.

I agree. Are you sure you cut the correct wire? Did you verify the wire from one end to the other?

Roy

I checked fuel pressure at the rail last night and it’s good. I’ll check MAF power and signal at the MAF and at the PCM connector this AM.

All the fuses, connectors, pins and wires at all of my work points checked out visually. I did see in the wiring diagram that the anti-theft and ignition wires were right next to the MAF signal wire, and they weren’t damaged, and when the wires were moved, the female pin connectors inside the harness moved, so they look fine.

I’ll just recheck everything again. Then check for spark.

Are you sure you cut the correct wire? Did you verify the wire from one end to the other?

Roy

As far as cutting the correct wire, I’ll recheck that, but it’s: 1) the same color (wire 492), 2) it aligns with the wiring diagram #52 , 3) it ohm-ed out (with beep and reading), but I’m going to check that again. That’s an obvious one that, if done, would be completely bone-headed and I’d be embarrassed, but it would be the issue. Uggggg.

So I went out and checked: the wiring vs. the diagram again, 2) my wire connections and solder ability, 3) insuring there were no shorts or anything, and 4) disconnected the MAF sensor.
I then tried to crank it and she started up (relief) but she was a bit rough. What I did to "fix" the issue from the night before I have absolutely no idea. I then reconnected the MAF as it was running and it kept running and actually smoothed out a bit. However, my Foxwell still gave me the MAF code " PO102, Mass of Volume Air Flow A, Circuit Low."

I'm going to get a replacement MAF sensor and put it in and see how she runs and if the code comes back.

Sound correct?

Correct.

Roy

So I put it all back together, with the new MAF sensor, and it started (had to pump the gas once) and drove it and it drove great; just like yesterday with the new sensor wire and the old MAF. My Foxwell still pulled the code, "PO102, Mass of Volume Air Flow A, Circuit Low" even though I erased it before starting it and again during the drive.

What do you guys think?

Should I try "flashing" the PCM/VCM to factory original with just the two calibration history's included or is it something else?

Closer, ever so much closer.

Again, thanks!

Start with flashing with the most current update.

Roy

I'm tracking down an older XP laptop as the free GM program requires XP Sp3 to run and we don't have one anymore. I'm not sure an emulator would work well as it will have issues connecting to the ports (I have read).

I'll let you know when I have it (hopefully today) and do the "flash."

I have the laptop, and I am installing a new clean version of XP Professional with SP3, and just takes some time (waiting) on these older computers.

Does this look like the most up to date GM program for my use: http://www.mediafire.com/file/bc92by7ao7fp1la/GM_2000NAO.7z/file

I cannot tell from that.

Did you go to the GM tech site for the most updated version?

Roy

It seems the PCM has the most updated software, and I cannot flash it without a Tech 2 scanner (which I don't have), but all I can do is check its values, and if I want, I could modify them like a fool, if I wish. Not gonna do it.

I drove her again and found these three details quite illuminating:
1) In order to start it, you must push the pedal (open the air valve), or it will simply spin the starter/engine; which I don't think is how this car is supposed to start, ie. it should be simply to turn the key. Correct? Why do you guys think this little detail occurring?
2) But once it starts, it idles well and drives with all the power one would expect.
3) The "service engine soon" light is on and my Foxwell tells me the same old code, "PO102, Mass of Volume Air Flow A, Circuit Low" even if I erase it, and then drive it again. This is a new sensor wire as well as a new MAF. As an aside, something keeps telling me the original MAF is still good.

As an aside, I had a friend tell me to disconnect the battery for a while, then reconnect it as this would allow the flash memory to be erased and the code might go away. Ever heard of that?

Forget about disconnecting the battery. That does nothing.

I think you have a bad PCM. Just because it has the most recent program does not mean it is working correctly.

Roy

Is the only way to test a PCM is to have it checked/reprogrammed the dealership?

It has to be done with the car, not off the car.

Unless you have the Tech 2, then no, you cannot peek inside.

Roy

Finished (though I had to go to a shop with a Tech 2 and basically rent it with the mechanic).

Everything is factory spec, and it idles and revs without issue. No trouble codes. Everything is within spec. when we looked over all the info in his Tech 2 readings.

When driving (though markedly better and gets up to highway speed great), still it seems the engine, as it is accelerating: feels that it either adjusts the fuel/spark a bit, or the transmission shifts prematurely into a higher gear or something (that's the only way I can describe it). It's weird to feel the car do something without driver input. Whatever it is is keeps the car from continuing its acceleration for a few seconds. If I give it throttle during the event, it downshifts and accelerates great through the issue. If I don't alter the accelerator, and keep it steady during the event, it waits a few seconds and then shifts to overdrive and feels normal.

Since I changed the fluid and filter when I first was alerted of the issue by my daughter during my maintenance work, and the old fluid was discolored (aged) and there was no metal dust or filings on the magnet, I'm wondering if I just need to allow her to drive it and change the fluid again in a few days and see if it flushes more of the old fluid that was trapped inside the torque converter?

You can try, yes. I would change it a couple times.

I doubt it has anything to do with the code at all.

Did he check for updates from the GM web site?

Roy

Yes, it was the most updated. The last update was:

I would try another PCM.

Roy

Really... interesting. So what's your thought process?

It may not be processing the information internally.

Roy

Also, I was wondering; what if the PCM and the engine is working as designed? There is the vacuum powered transmission modulator that might be a issue. Now I have read up a bit on issues this failure causes, and therefore realize hard shifting and lack of shifting at all seems to be the main complaints, but what if it has a vacuum leak in the hose or a sticky spot in the moving component within the unit?

(rabbit trail perhaps, but car issues always have lots of those)