Check engine light, code P0101

Okay, from here on in you are going to need a scan tool to monitor data. it could come down to a wiring issue. I attached a description of the code and possible solutions beyond the obvious.

Roy

CIRCUIT DESCRIPTION
The mass air flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The powertrain control module (PCM) uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has the following circuits:
- An ignition 1 voltage circuit
- A ground circuit
- A signal circuit

The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage to produce a frequency based on the inlet air flow through the sensor bore. The frequency varies within a range of near 2,000 Hertz at idle to near 10,000 Hertz at maximum engine load. The PCM uses the following sensor inputs to calculate a predicted MAF value:
- The manifold absolute pressure (MAP) sensor
- The intake air temperature (IAT) sensor
- The engine coolant temperature (ECT) sensor
- The engine speed (RPM)

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. If the PCM detects the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value DTC P0101 sets.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0102, P0103, P0106, P0107, P0108, P0120, P0220, P0442, P0443, P0446, P0449, P0455, P0496, P2135 are not set.
- The engine is cranking or running.
- The ignition 1 signal is between 11-18 volts.
- The throttle position (TP) indicated angle is less than 95 percent.
- The change in the TP indicated angle is less than 5 percent.
- The MAP sensor is more than 17 kPa.
- The change in the MAP sensor is less than 3 kPa.
- The above conditions are met for 1.5 seconds.

CONDITIONS FOR SETTING THE DTC
The PCM detects that the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value for more than 4 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
- Inspect the harness of the MAF sensor to verify that it is not routed too close to the following components:
- The secondary ignition wires or coils
- Any solenoids
- Any relays
- Any motors
- A low minimum air rate through the sensor bore at idle or during deceleration may cause this DTC to set. Inspect for any vacuum leak downstream of the MAF sensor.
- Inspect for any contamination or debris on the sensing elements of the MAF sensor.
- Inspect the air induction system for any water intrusion. Any water that reaches the MAF sensor will skew the sensor and may cause this DTC to set.
- A wide open throttle acceleration from a stop should cause the MAF sensor parameter on the scan tool to increase rapidly. This increase should be from 3-10 g/s at idle to 170 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system.
- A high resistance of 15 ohms or more on the ignition 1 voltage circuit may cause this DTC to set. A high resistance may cause a driveability concern before this DTC sets.
- The barometric pressure (BARO) that is used to calculate the predicted mass air flow value is initially based on the MAP sensor at key ON. When the engine is running the BARO value is continually updated near wide open throttle. A skewed MAP sensor will cause the calculated mass air flow value to be inaccurate and may result in a no start condition. The value shown for the MAP sensor display varies with the altitude. With the ignition ON and the engine OFF, 101 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 305 meters (1,000 feet) of altitude.
- A high resistance on the 5-volt reference circuit of the MAP sensor may cause this DTC to set.
- A high resistance on the low reference circuit of the MAP sensor may cause this DTC to set.
- If the condition is intermittent, refer to Intermittent Conditions. See: Computers and Control Systems > Initial Inspection and Diagnostic Overview > Intermittent Conditions

TEST DESCRIPTION

Steps 1-4
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Steps 5-6
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Steps 7-9
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Steps 10-15
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The numbers below refer to the step numbers on the diagnostic table.
5. This step will determine if the MAP sensor pressure is within the proper range for a given altitude.
6. This step will determine if the MAP sensor voltage is within the proper range at idle.
7. This step will determine if the MAP sensor responds properly to the change in manifold pressure.
8. This step will determine if the TP sensors are operating properly.
9. This step will determine if any mechanical faults have caused this DTC to set.
10. This voltage drop test will determine if high resistance has caused this DTC to set.

Alright so I went through and tested everything in the description you posted and all looks good. But I have an update as of today, I think I might be leaning towards a fuel delivery problem. I know this is kind of out of no where but let me explain. so right before I bought this truck there was a “new” fuel pump assembly installed. and for the last week or so I have had a code for the fuel tank pressure sensor, after doing a few test I have determined it has failed. Now, most new fuel pump assembly’s come with a new fuel tank pressure sensor correct? So if the assembly that was put in is actually brand new then the chances of it failing this soon are much lower.. where as if they put in a used pump assembly, the chances are obviously much greater.. and that is honestly what I think they did. I also believe this because the pump has been making a high pitched electrical noise.. and six times in the last two weeks it has given me trouble starting and every time it sounded like a fuel delivery problem.. so basically I have all these clues and at this point from what I can see there all pointing to the pump.. any opinions on this?

Okay, the fuel pressure sensor can be replaced by itself. most pumps do come with it but there are the cheaper ones that do not and have to change the one from the old one to the new unit.

the fact that the pump makes noise is no good. it should never make any noise except a rumble when it is working.

it does sound like you have a pump issue.

check this at rockauto.com.

https://www.rockauto.com/en/catalog/chevrolet,2003,silverado+1500,5.3l+v8,1412086,fuel+&+air,fuel+pump+&+housing+assembly,10147

Alright hmm. So I am thinking that must be what they did, either a used pump or a cheap one. and I can upload a video of the noise if you would like, it is a really high pitch noise and it really sounds like it is electrical. It makes this sound from the second I turn the key on till the second I turn it off and it is clearly heard from standing beside, or even a distance from the truck. and oh yes I love rock auto they are definitely my number one online parts site. If I do have to get a new pump i will definitely go with either the AC/Delco or the Delphi pump assembly they have on there. I checked a week or two ago but that was before it started giving me trouble starting, so I am going to check the fuel pressure again when I get home, at KOEO and while running/under load and see what I get for numbers.

Okay, give me a video of the noise.

Roy

Alright here is the noise from the pump. I recorded from right under the tank. and towards the end I put my phone against the tank a few times and you can hear a change in pitch, not just in the video I could hear it myself too. like a signal or something from my phone was changing the pitch/frequency of the noise.

Okay, I would replace the pump.

Roy

Alright, I think I am going to keep my fuel pressure gauge hooked up until it gives me trouble starting again witch I imagine will not be any longer then a day or two. But just to be sure just because money is tight right now. I will post either as soon as I have an update or once I replace the pump with the results.

sounds good.

Roy

Well of course now that I have had the gauge hooked up it has not acted up. But I have been looking into something else, the other day I was watching random things on the scanner on hot and cold starts and I noticed what seems to be my TPS malfunctioning, mostly when the engine is hot. It only happens at idle & start up though. and what exactly that is happening is, at start up on a cold start (so this is key on right before starting) the throttle position is 9%. Witch seems normal, I mean it starts normal too at this time. and then from there the throttle position slowly goes down to around 2-3% (engine at operating temperature) this seems low even for idle? But anyways, on start up when the engine is warm, (key on right before starting) the throttle position is at 19.2%? This seems high. and not to mention every time it is this high right before start up, the engine feels like it kicks back literally the second it fires up. Any opinions on this? Any chance you know or have access to the specs for the TPS on this truck? I believe 2003 to 2006 have this same TPS sensor. I know not all do though. This one is the eight wire.(drive by wire) where the others have the three wire sensor. The specs I am looking for though are either throttle position percentage or voltage at idle and at start up.

Okay.

the readings are normal.

the reason you see high percentages is the PCM open the throttle a little when cold for air intake into the system. when it run, it will be low as the plates have to be closed at idle. when warm, the plates open a little more for easier starting.

the spec for idle running is .5 to .75 volts on the TPS. wide open throttle is about 4.9 volts.

Roy

Alright thank you very much. I will check that against what I got for voltage once I get home and post what I had. Also, I was curious because I can give a little throttle and hold it around 700 to 800 rpm's and it will run like a charm at this moment. But once i let off from that it will bog down real low and almost stall. But, if I rev it quickly above that it will come back down to idle like normal.

Okay, one thing you can check is the EGR valve. make sure it is not partially blocked by carbon in the valve itself.

Roy

this truck does not have an EGR luckily. Or an IAC. Being said I bought this specific truck hoping/expecting to have no/little idle issues, lol, but I guess I was wrong. But I guess it is just figuring out where to go from here being that your normal idle causes are out of the question (no EGR, no IAC, no vacuum leaks, throttle body and intake are clean).

I mean as much as it seems like a vacuum leak being that the problem goes away at higher rpm's, I have checked for vacuum leaks at least five times now. using multiple methods too.

Do you have a scan tool that can read live data? if you do, I need the long term trim reading. that will tell us if you have a vacuum leak.

Roy

Yes I do! I actually have it with me right now too. and It can graph up to three live pids at once too so just to keep in mind if anything like that would be helpful I could absolutely upload a video of whatever you would like to see. But the long term fuel trims are, bank 1- 11.7% bank 2 - 7.8% and this is at idle.

Both are high. they should be around 3% to 4%. that does indicated a vacuum leak.

Check the PCV valve and make sure it is not stuck open
Remove the oil fill cap and put your hand over the tube. see if you feel vacuum.


Roy

Alright thank you. I thought they were a bit high but I did not know exactly where they should be. Plus all the times I checked for vacuum leaks but I guess I need to dig a little deeper!

The PCV valve on this truck does not close, it is basically a fitting In between the hose and valve cover that has a small hole in it to limit airflow. Alright I will do so and poke around a bit more once i get home here shortly.

Okay, keep us updated.

I finally got it! You are exactly right, vacuum leak. I do not know how I did not find it the first five times, probably because of dirt etc. Because this time I took my shop vacuum and air gun and loosened up/sucked up most of the dirt around the intake manifold and then I used brake clean to check for vacuum leaks. Right by cylinder number one there is what must be a good size leak. Once I sprayed in that area a few times the truck started stuttering (for lack of a better word) pretty good. I think that is what did it, the brake clean cleaned away the rest of the dirt that must have been partially blocking the leak. But now that I sprayed brake clean in that area a good five or so times you can clearly hear a vacuum leak. So as soon as I find a set of the updated gaskets that will not cost an arm I will order them. put them on soon as they come and see how it idles, then I will call the rough idle a confirmed fix. Thank you for everything you have helped me with to get me to this point I appreciate it very much!

You are welcome. let me know how it works after the repair.

Roy

Alright, so I installed the new gaskets. The old ones were leaking bad, on the old gaskets I can see where dirt was partially blocking the vacuum leaks and I mean really only a few of the gaskets were not leaking. There was tons of dirt around the gasket surfaces. So I got the gasket surfaces and all under the manifold all cleaned up, cleaned up the intake ports too along with the ports and everything on the manifold itself. First start up after replacing the gaskets it was still idling rough but it got better and today it has went to basically an intermittent rough idle. I had a couple times today where it took a few tries to start. Also, I still have the engine kickback on hot starts. Looking at what I know, i I know it is getting air. So it has got to be either spark or fuel right? The readings from the O2’s at idle get up to 0.800 volts so as far as I know this means it is getting plenty of fuel? So if this is true, and if the rough idle and hard starts have the same cause, then it would be spark? Oh also, I forgot to mention earlier in the post, the long term fuel trims at idle are now as follows, bank 1, 4.7% bank 2, 0.8%.

Trims look good now. that is where they belong.

With those readings, I do not see an issue with spark. I think it may be injectors. They may be dirty and have carbon build up from the fuel. additives have no effect on cleaning. they must be cleaned in direct injection of the cleaner. shops have the tool to do this. that is when they disable the fuel pump and run the engine off the cleaner. works very well.

Roy

Oh alright, thank you. I will look into this!

Okay, keep me updated.

You are getting there.

Alright so sometime in the next few days I am going to go down to my buddy’s shop and we are going to clean the fuel injectors. he has one of those tools you were talking about. Also, I was wondering if there was a chance you knew what the spark timing advance is supposed to be around at idle on this truck?

That is controlled by the PCM. It will vary. There is no specific figure.

Roy

Alright thank you. I had to kind of pause on this for a few days to get some stuff done for state inspection. But I will post an update once I get the injectors cleaned. I think before I get the injectors cleaned tho I might take the fuel rails off at the shop just to take a peek inside the rails because I read on a few forums about people having a rough idle due to rust/corrosion in the fuel rails on these trucks. I am going to look into that more in the meantime. Have you heard of such a thing happening?

Yes, clogged fuel injectors will cause this issue. if there is rust or debris, that came from the tank. you will need to start at the tank and drain and flush along with all the lines and fuel filter.

Roy

Alright thank you. I will make sure we closely inspect everything, planning on getting that done tomorrow. I will let you know the results.

Good, keep us updated.

Roy

Absolutely. on my way down to get that done now. so I will post results later or first thing in the morning. But I have a question before I forget, so the radiator fan in this truck as far as I have noticed basically has two speeds (it will turn on low when the engine is running and speed up about twice as fast or so, for example when idling for a while) well once in a while lately once I start the engine cold it will kick on at the higher speed. any idea of what could be causing this?

The coolant sensor is what controls the fans. The ECM commands speeds based on the input from the coolant sensor. Check that sensor to be sure it is reading correctly.

Roy

Alright so it has happened just about every day since I posted that, sometimes once a day sometimes two to three times. I checked the temperature every time with the scanner and half of the time it was around 115 degrees and the other half it was cold start and at outside ambient temperature witch has been around seventy degrees lately. When this happens I will start it, the fan will immediately be on high and it will stay on high until I have driven for a minute or two at at least thirty five mph. Also I got the injectors cleaned and for the most part is has been running better, but once in a while maybe a few times a day If that (I drive a lot) I will still get an Intermittent rough idle at normal operating temperature. It is not quite as rough as it was before though. But it is always with the engine hot. It runs like a charm when it is cold.

Okay.

This is sounding more and more like the PCM is commanding this fan on for the wrong reason.
Have you had a shop check this for you? The PCM is what controls the fans on and off based on the coolant temperature.

Roy

No I have not. I usually do everything myself with help from people like yourself when needed, but for a couple reasons one being I have loved working on vehicles since I was a kid and two money has been tight. I am currently trying to save up money to go to UTI. I think I might start poking around with it before I jump into anything. Maybe start by hooking my multi-meter to the output from the PCM to the fan and see what I get when it is on low and high. Then start plugging into different inputs to try and figure out where the “high on” signal is coming from.

Keep me updated.