MAF or MAP
01-11-2014, 06:35 PM
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MAF or MAP My 03 Silverado with LS1 threw a MAF code. It runs rough occasionally at around 2200 rpm then goes away. I've replaced MAF sensors with reman and with new but still getting code. could bad map sensor cause MAF code and sluggish running
01-11-2014, 08:47 PM
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Which MAF code? It matters.
Pull the MAF connector and run it. If it runs better
then your MAP sensor is good and the MAF is bad.
If it doesn't run or runs terribly then the MAP might
be. Although MAP failures seem pretty uncommon
unless you have a hell of a backfire.
Pull the MAF connector and run it. If it runs better
then your MAP sensor is good and the MAF is bad.
If it doesn't run or runs terribly then the MAP might
be. Although MAP failures seem pretty uncommon
unless you have a hell of a backfire.
01-12-2014, 05:16 AM
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No cats. Had them removed. Sometimes, when I first start it up, it idles ok but when I give it some gas it will miss and pop some but only for a few seconds. It runs fine until I get to around 2200 rpm. it's almost like a dead spot in gas pedal but it goes away at higher rpm's (doesn't always happen) and when I'm cruising at highway speeds occasionally I can feel a slight stall for maybe 1 second then back to normal. Like I've said, I have replaced MAF sensor twice so I do not believe that's the problem but the code is for MAF. Will check code again and see exactly which code and post here.
Last edited by James Pope; 01-12-2014 at 06:18 AM.
01-12-2014, 07:12 AM
#5
First, it matters which MAF code. There are three.
With the engine idleing wiggle the connector on the MAF, and flex the wires while watching the MAF numbers on your scan tool. If the numbers move around much (like 3 or 4 grams/sec) and/or the engine runs differently you may need to buy a MAF pig tail (new connector with a couple inches of wire) to splice into place. The GM parts dept used to sell those. Not an uncommon problem.
Don't ever buy a reman MAF!
With the engine idleing wiggle the connector on the MAF, and flex the wires while watching the MAF numbers on your scan tool. If the numbers move around much (like 3 or 4 grams/sec) and/or the engine runs differently you may need to buy a MAF pig tail (new connector with a couple inches of wire) to splice into place. The GM parts dept used to sell those. Not an uncommon problem.
Don't ever buy a reman MAF!
01-12-2014, 12:00 PM
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Tried disconnecting MAF and could barely get truck started. Going to auto parts store to pull code again and get exact error and also to check for bad connection. Then will try MAP
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01-15-2014, 04:08 PM
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It's back 
Light is back on. Going to pull code tomorrow but I already know. P0171, P0174 and P0101
I've replaced MAF and MAP. I still get a hesitation occasionally. What are chances new MAF bad? This is driving me up the wall. I plan on taking a 1500 mile trip in two weeks.
Light is back on. Going to pull code tomorrow but I already know. P0171, P0174 and P0101
I've replaced MAF and MAP. I still get a hesitation occasionally. What are chances new MAF bad? This is driving me up the wall. I plan on taking a 1500 mile trip in two weeks.
01-16-2014, 11:07 AM
#11
It's back
Light is back on. Going to pull code tomorrow but I already know. P0171, P0174 and P0101
I've replaced MAF and MAP. I still get a hesitation occasionally. What are chances new MAF bad? This is driving me up the wall. I plan on taking a 1500 mile trip in two weeks.
Light is back on. Going to pull code tomorrow but I already know. P0171, P0174 and P0101
I've replaced MAF and MAP. I still get a hesitation occasionally. What are chances new MAF bad? This is driving me up the wall. I plan on taking a 1500 mile trip in two weeks.
I know you have to be getting tired of this. Hope you find it soon.
01-16-2014, 02:18 PM
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P101: "The PCM compares the actual MAF sensor frequency signal to the predicted MAF value. This comparison will determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. DTC P0101 sets if the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value."
This is not necessarily an outright fail, it can come about
from some discrepancy between speed density or alpha-N
air mass models and what the MAF reports. If (say) the
VE table is badly edited, or not edited at all but significant
airflow modes made, this code could pop with a perfectly
fine MAF (as seems to be the case here). A MAP sensor
that reads a crazy voltage could be believed and used to
set the "expectation" against which a good MAF may
fail.
P0171/0174 are bank lean codes driven from the trimming
process. The fueling cannot be enriched enough to make
sensors switch, is the thinking. But these tests can also
be spoofed by bad sensors, or too cold to function.
It seems to me that you do not have enough insight to
the real goings-on. You need to look at things like what
the real MAF output frequency is, whether it responds
to real motor airflow with increasing frequency and
sits somewhere sensible at idle and so on. You need
to look at O2 sensor voltage waveforms and see if
they are pegged low, or just struggling, or pinned to
the fault level (~450mV), or are credibly functioning
and telling you about a true lean condition. That is an
interpretation, to great extent, but critical to debugging.
This is not necessarily an outright fail, it can come about
from some discrepancy between speed density or alpha-N
air mass models and what the MAF reports. If (say) the
VE table is badly edited, or not edited at all but significant
airflow modes made, this code could pop with a perfectly
fine MAF (as seems to be the case here). A MAP sensor
that reads a crazy voltage could be believed and used to
set the "expectation" against which a good MAF may
fail.
P0171/0174 are bank lean codes driven from the trimming
process. The fueling cannot be enriched enough to make
sensors switch, is the thinking. But these tests can also
be spoofed by bad sensors, or too cold to function.
It seems to me that you do not have enough insight to
the real goings-on. You need to look at things like what
the real MAF output frequency is, whether it responds
to real motor airflow with increasing frequency and
sits somewhere sensible at idle and so on. You need
to look at O2 sensor voltage waveforms and see if
they are pegged low, or just struggling, or pinned to
the fault level (~450mV), or are credibly functioning
and telling you about a true lean condition. That is an
interpretation, to great extent, but critical to debugging.
01-16-2014, 03:53 PM
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P101: "The PCM compares the actual MAF sensor frequency signal to the predicted MAF value. This comparison will determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. DTC P0101 sets if the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value." This is not necessarily an outright fail, it can come about from some discrepancy between speed density or alpha-N air mass models and what the MAF reports. If (say) the VE table is badly edited, or not edited at all but significant airflow modes made, this code could pop with a perfectly fine MAF (as seems to be the case here). A MAP sensor that reads a crazy voltage could be believed and used to set the "expectation" against which a good MAF may fail. P0171/0174 are bank lean codes driven from the trimming process. The fueling cannot be enriched enough to make sensors switch, is the thinking. But these tests can also be spoofed by bad sensors, or too cold to function. It seems to me that you do not have enough insight to the real goings-on. You need to look at things like what the real MAF output frequency is, whether it responds to real motor airflow with increasing frequency and sits somewhere sensible at idle and so on. You need to look at O2 sensor voltage waveforms and see if they are pegged low, or just struggling, or pinned to the fault level (~450mV), or are credibly functioning and telling you about a true lean condition. That is an interpretation, to great extent, but critical to debugging.
