Ugh, P0101 again. Rich this time.

J

Jonas

Joined
Jul 13, 2020
Messages
625
Hey gang. I just got a CEL and the only code was P0101. I had this happen about 4-5 months ago and replacing the MAF sensor fixed it (after cleaning the old one and other things didn't work.) However, back then I also got a lean code (P0171) and my LTFT was high double digit positive. This time it's the opposite-trims are double digit (as high as 25%) negative. I find it hard to believe my new Denso OEM MAF sensor would only last a few months. I'm going to try cleaning it again, but I don't hold out much hope that it will help. Any advice? Ideas?
Thanks in advance,
Jonas
 
That code by itself, to me, points to a MAF issue.

If you view scan data, does the manifold pressure seem in line (high vacuum at idle, near zero under load, etc.)? How about throttle position?

If the LTFT is -25%, it should be throwing a rich code. In that case, I'd suspect O2 sensor or faulty injector perhaps.
 
92saturnsl2 said:
That code by itself, to me, points to a MAF issue.

If you view scan data, does the manifold pressure seem in line (high vacuum at idle, near zero under load, etc.)? How about throttle position?

If the LTFT is -25%, it should be throwing a rich code. In that case, I'd suspect O2 sensor or faulty injector perhaps.
Click to expand...
Thanks. I didn't check manifold pressure or throttle posistion, but I will. Fortunately there was no rich code. It does seem like a MAF malfunction since the grams-per-second reading were going haywaire, like 25gps at about 1200 rpm. I'll try cleaning it in the morning. I had recently run a few tanks with fuel injector cleaner around the same time this started, but I highly doubt that's related. I also doubt a 5 month old MAF would malfunction out of the blue, so here\s hoping it's just dirty.
 
Last edited:
Can you access MAF Grams Per Second data? Normal idle is usually around 2.5gps.....If it reads much higher like 3.5-5gps, The MAF is over reporting air flow.

Where did you purchase the MAF?
 
clinebarger said:
Can you access MAF Grams Per Second data? Normal idle is usually around 2.5gps.....If it reads much higher like 3.5-5gps, The MAF is over reporting air flow.

Where did you purchase the MAF?
Click to expand...
Yes, the MAF is over-reporting for sure. IIRC, the prvious one was under-reporting when I got the lean code. I bought the MAF sensor at Advance Auto. It was a Denso and other than the slightly different logo print, it looked identical the the 12 year old one it replaced.
It could just be dirty this time. I did clean the throttle body and otherwise disturb the air box and snorkel some recently, so I'll spray it down in the morning and report back.
 
Just read this review on the AAP website:

(1 star)
Would not recommend. Not OEM Quality
Submitted 2 years ago
Bought this after my OE Maf sensor went bad. The first one lasted about 1 months before the mpg dropped. Replacement was not much better, uneven rpm and bad mpg. Even though Denso is OEM for toyota,I returned and bought from a dealer. Works much better, WOULD NOT RECOMMEND

Bottom Line No, I would not recommend to a friend


Sounds familiar.
Also, it was listed as a fit for the matrix, but not the vibe. The Vibe/GM one is a Delphi brand.
 
This thread is why I like coming to this forum! Hopefully a $50 investment will render a positive fix for you.
 
Per mk378's suggestion, I checked the MAF with car on, engine off and it read steady at 0.81 grams per second. Apparently it is supposed to be zero.
LTFT was at -21%
 
Also, I'd have to order the correct sensor. How bad would it be to drive around until arrives? I'm guessing not good.
 
Kokopelli34179 said:
I had that code on my Nissan. It wasn't the MAF at all, in my case. It ended up being a cracked air intake hose. Also, there was a Nissan TSB saying that the ECU needed reflashing, as well.
Click to expand...
Sounds like that would cause you to run lean. Were the fuel trims high positive? Mine are high negative which I've never seen before on my car.
 
*update*
I Cleaned the MAF with CRC cleaner. I Didn't think it would help, but the wire that faces the airflow was a tad darker/duller than the others.
Drove around for 30 minutes; all the sensors were "ready."
Now at idle:
STFT: -0.8
LTFT: 0.0
Success!
 
Jonas said:
Sounds like that would cause you to run lean. Were the fuel trims high positive? Mine are high negative which I've never seen before on my car.
Click to expand...
I'm not really sure. I don't have a sophisticated tool for that. All I know is I had that code, and it was due to something else, not the MAF sensor itself.

I'm glad you got your issue fixed. Those hot wires, or whatever they are called, can be a real pain to deal with.
 
Kokopelli34179 said:
I'm not really sure. I don't have a sophisticated tool for that. All I know is I had that code, and it was due to something else, not the MAF sensor itself.

I'm glad you got your issue fixed. Those hot wires, or whatever they are called, can be a real pain to deal with.
Click to expand...
So i have discovered :) I couldn't even tell it was dirty at first, looking very closely under a bright light. However, when I sprayed it down, I noticed one of the wires became ever so slightly lighter in color and matched the others. The car also started quickly and had more zip. Before it felt like I had a stuck caliper or something. It seems like the air filter really is the most important filter as many have said here.
 
Kokopelli34179 said:
I'm not really sure. I don't have a sophisticated tool for that. All I know is I had that code, and it was due to something else, not the MAF sensor itself.

I'm glad you got your issue fixed. Those hot wires, or whatever they are called, can be a real pain to deal with.
Click to expand...
It's not unusual to get a code for something (MAF, MAP, O2 sensor, etc.) and have the problem lie with a different, usually related component.

Sometimes the ECU determines some sensor's values are not in range, but it doesn't know why, so it might trust another faulty sensor's data, and put the blame on a good component. Scan data is incredibly valuable as opposed to just swapping parts. I always try to eliminate possibilities as much as possible using scan data. MAF codes along with positive fuel trims (the O2 sensor providing feedback that the mixture is lean) is often a vacuum leak, as in your case. The air that gets introduced that isn't metered by the MAF makes the mixture lean. The OP has MAF code with negative fuel trims (ECU having to subtract fuel in response to O2 input) which, for me, rules out a vacuum leak.
 
92saturnsl2 said:
It's not unusual to get a code for something (MAF, MAP, O2 sensor, etc.) and have the problem lie with a different, usually related component.

Sometimes the ECU determines some sensor's values are not in range, but it doesn't know why, so it might trust another faulty sensor's data, and put the blame on a good component. Scan data is incredibly valuable as opposed to just swapping parts. I always try to eliminate possibilities as much as possible using scan data. MAF codes along with positive fuel trims (the O2 sensor providing feedback that the mixture is lean) is often a vacuum leak, as in your case. The air that gets introduced that isn't metered by the MAF makes the mixture lean. The OP has MAF code with negative fuel trims (ECU having to subtract fuel in response to O2 input) which, for me, rules out a vacuum leak.
Click to expand...
Indeed. If I wasn't able to see that my Airflow grams per second reading was too high and going haywire, I would have bet on a leaky injector. When I got a lean code months ago, I would have sworn I had a vacuum leak. It was the MAF sensor both times.
 
@Jonas - did you have any drivability issues with the dirty MAF or was the only reason you noticed was from the CEL? All the GM 3800's I have/had get a bit of hesitation when they start getting dirty, long before the CEL comes on.
 
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