2003 GMC 5.3L check engine codes P0171, P0101, P0102, P1514

I have the following codes: P0171, P0101, P0102 and P1514

2003 GMC 5.3L 219,506 miles, serial number: 2GTEC19T331280635

I have replaced the engine coolant temp sensor at 218,314 miles as per instructions of Autozone. Light did go out for a brief period of time but came back on. Removed and replaced throttle body at 218,506 miles, no change.

Engine runs smooth but is idling a little higher than previous (now 800, before 600).

Also have a hard time starting after sitting overnight, turns over several times, starts but stumbles and dies, restart will usually work second time, will run rough but then settle down after about fifteen seconds. Acts as though it is out of fuel.

Your assistance in this matter is greatly appreciated,

Do you own a scan tool, or have access to one? Clearing the codes and observing the fuel trims at idle and while driving will be the next best step for the P0171 and MAF codes. We're especially interested in the MAP and BARO readings KOEO and at idle.

The hard start after sitting overnight definitely matches a fuel problem. May or may not be related to the other codes. How about a fuel pressure gauge set? The fuel rail on your 5.3 has a Schrader valve for easy pressure testing.

Ignore the P1514 for now. That code doesn't point to a specific problem with the TAC, but a disagreement between the measured airflow of the engine, and the calculated airflow (like in a speed density system). P1514 is not the problem, but a symptom of the problem.

I have just purchased a Autel MX808 scanner and have not had time to set up.

My fuel pressure was 30 psi at idle and once the engine was shut off would bleed down to zero in about three hours.

Checked fuel pressure regulator by disconnecting the vacuum line, not change.

Removed and replaced the fuel filter, no change.

I am in the process right now of changing out the fuel pump. Once that is completed i will share my fuel pressure readings and outcome.

Then i will probably need some help with the scan tool. I am real old school and all this technology has severely humbled me.

Congrats on the Autel! See what MAP/BARO PIDs it gives you, and we can go from there. In short, we want to make sure the MAP sensor reads atmospheric pressure with the key on but engine off. That's the BARO reading. If it's not reading correctly, that can skew the airflow calculation, leading to your P1514.

30 PSI is definitely not enough. If the pressure comes up to spec after pump replacement, then you may end up fixing your P0171. We can verify that with scan data afterwards.

Tyler,

The fuel pump was wrong (needed one with a square connector), will have to wait till Monday morning to resolve the low fuel pressure problem. Will keep you posted.

Bruce

As long as you're waiting, have you verified power and ground at the existing fuel pump connector? Asking mostly because of the low fuel pressure reading, which can be indicative of a voltage drop issue. You could even check for voltage drop using the old pump if you already have it out of the tank.

That way, if there is an issue, you don't have to drop the tank/remove the bed again.

Tyler,

For some reason I am not getting notifications of when someone posts a reply, is there a setting I have to make?

Removed and replaced the fuel pump. Had to settle for the initial pump assembly (which meant I had to cut my harness and slave in a new connection).

Pressure at the manifold is now 52 psi. Do you think I should change out the fuel pressure regulator? The specifications call for 60 psi.

I have learned how to basically navigate with the Autel MX808. I cleared the codes as per your instructions.

I will attached the PDF report file for your review.

Your attention in this matter is greatly appreciated,

Bruce

Have all those codes returned already? Because I see several of them that haven't run. If they have, then you fixed one problem with the fuel pump, but not THE problem.

I think now is the time to look at your scan data at idle and 2500 RPM to get an idea of what the fuel trims are doing. Don't forget to check the MAP and BARO readings with the key on, engine off.

Tyler,

I do not know if they have returned. Have not run since I cleared them, was waiting for further instructions from you.

Not sure how to run the MAP and BARO.

Remember I am new to all of this (old school). Can you step me through?

Bruce

Tyler,

I have just finished a thirty mile trip and the check engine light has not come back on. I have not performed another scan to see if any codes have reappeared.

The hard start issue is resolved. The fuel pump seemed to fix this problem. I still have fuel pressure that is not up to specifications. The pressure is at 50 psi and the specifications call for 60 psi.

Ever since I removed and replaced the throttle body I am having Idle and RPM issues. This change this was one of the recommendations from the AutoZone scan (prior to my purchase of my own scanner).

When you first start the engine, idle is around 700-800 RPM. Idle will come down to about 600 RPM after a few minutes.

When I place the transmission in Drive the idle surges to 1,000 RPM. Sometimes it comes back down to 600-700 at other times no.

While driving in town, cannot maintain speed at 30 MPH, engine will not idle back down, runs at 1,100 RPM. When I shift to neutral, RPM surges to 1,200 - 1,500 RPM, and will then settle down to about 600-700 RPM.

It now requires more braking effort to stop as the engine will not always return to an acceptable idle range.

Your advise in this matter is greatly appreciated,

Bruce

Hey Bruce! I haven't forgotten about this thread, just busy with work. :blush: I'll get back to you on the idle ASAP.

Tyler,

Not to worry, I understand.

I am thinking about reinstalling the old throttle body and see what happens.

Bruce

Did you get the throttle body on and sealed up correctly with no leaks when you installed it?

I'd hook up and see if you have any codes that give you any direction in which way you want to go.

I am guessing the Code scan you posted was a prescan and not a post scan? That's what shops, techs , etc are doing anymore as a way of showing the customer what the vehicle came in with and what it's leaving with.

It's also a good sales tool when used properly to help facilitate explaining things to some customers who may not fully understand what's going in in the vehicle.

IF it was a prescan don't Do the post scan yet but either see if you can do another prescan or a scan of the vehicle to know if at all if it has any current codes whether the lights on or not as there's hard and soft codes. There's also a flashing check engine light and with that you shut the vehicle down and check it over, perform a scan before starting it again as the flashing light means it's critical vs a steady on check engine light or "CEL" as some people call them.

Not trying to be a salesman but if you're old school one thing that will help is to pickup scannerdanner's book over at www.aeswave.com . Yes it's $99 but once you read it cover to cover you'll gain a more appreciative understanding of today's more modern electronically controlled engines and the troubleshooting knowledge you'll gain from it. It's basically the same thing Paul teaches when he teaches his Automotive Tech Class at the local community college where he's a teacher.

Another good way to learn and watch alot....... of videos of case studies on various vehicles is subscribe to the premium side of this website under the dropdown menu. Yes there's a monthly fee but the knowledge you'll gain and be able to reference is worth it and then some.

Anyways back to your vehicle. Being in the reply on mobile I can't recall the year of it but my 04 Chevy Tahoe runs around low to mid 50's for the fuel pressure of the top of my head from what I recall.

I'm going to take a stab at a couoje things and get corrected so please don't be confused by me as Tyler helps my thought process when I screw up and this'll probably be a moment.

Check all connections to the throttle body and see that they're all secure and fastened up as they should be.

Was the throttle body replaced as they suggested as sometimes just cleaning them works wonders.

Don't ever believe the Code readers and their suggesters in the parts stores. If I sold parts based off code scans all the time I'd be getting wealthy and Tyler would've developed a auto part suggester tool that loads the parts cannon and it would fire the parts at you automatically as the parts store did and didn't work initially.

I can't recall if there's a relearn involved with replacing the throttle body but I'm guessing there is.

IF you can watch your fuel trims and 02 sensor readings these may give you a indication. There's plenty of videos on YouTube in regards to fuel trims. Do a google search or search in YouTube and look for ones from Scannerdanner, watch those and take note. Scannerdanner does have some videos on YouTube free yet as he posts some over there because it will drive people to this site I feel. Probably his marketing dept (Tyler, or others who help him with the website.. Lol)

You could also try cleaning you MAF sensor. Don't use a brush or touch with your bare hands. They actually make a spray cleaner for it. Don't use brake parts cleaner unless you want to buy a new one. They're touchy at times.


Best advice is to do a Youtube search on "how to clean your MAF". It's not difficult at all and only takes minutes to accomplish. IF it's been awhile once you get things running right I'd check your air filter, spark plugs, spark plug wires, etc....

Hope some of this helps you until Tyler slows down. It's Fri though so if he don't work weekends he'll probably be back before we know it.

Sent from my SM-N960U using Tapatalk

Dtnel,

After I had replaced the fuel pump, I cleared all the codes.

As I had previously indicated, I did not have a check engine light once the codes were cleared.

I took a thirty mile trip and then performed a new scan, no codes, system clean except for one body code B2355, driver seat module.

There were no installation issues with the throttle body. Removed the new throttle body and reinstalled the old throttle body. RPM issues are resolved. This was a brand new OEM throttle body, wish I had some recourse with regards to the part. I was told the throttle body was causing DTC P1514, throttle body performance.

The throttle body was replaced per instructions.

You had touched on the subject if there was a relearn for the throttle body. Some of the articles I pulled up suggested that, but then some others discounted it. So I am not really sure if there is a relearn. The old throttle body did not need any teaching.

I also RR the fuel pressure regulator as my pressure was out of specification. 50 psi versus the 60 recommended. The pressure is still not within specifications, which is frustrating. Pressure is still at 50 psi.

It seems that all of my check engine light issues was the result of a low fuel pressure condition. With all that the ECM monitors, I am surprised that it does not monitor rail pressure. I was surprised to learn from Tyler that it monitors barometric pressure, that fact blew me away.

I will probably purchase the book you recommended to me. I am not doing this as a business, just trying to keep all of my equipment serviceable and operational. Most (90%) of my repairs are scheduled maintenance. I do not like being left in the dark and guessing so I will probably invest some more and get the book.

If you could pass this along to Tyler, I would appreciate it.

Bruce

Catching up with the thread. :blush:

bkreft, so you reinstalled the old throttle body and all is well now? If so, glad to hear it! Did your MX808 offer a throttle relearn procedure anywhere? Might be hidden under 'Hot Functions', if you feel like looking.

About the fuel pressure, what you're seeing may be normal function of the regulator. Have you tried checking fuel pressure with the regulator vacuum hose disconnected? That should cause the regulator to close and indicate a higher pressure. Hopefully, closer to 60 PSI. :silly:

You can also look at the fuel trims to see if the engine is still running lean or not. Pull up the short term and long term trims on both banks from the scan data and see what you have at idle and 2500 RPM.

The classic rule with fuel trims is that we like to see the total trim on one bank within 10% of zero. Zero represents no trim (excellent), positive numbers are adding fuel, negative are subtracting. So, if your short term trim on bank one was 6%, and the long term was -8%, that'd be a total of -2%.

With your fuel pump and low fuel pressure, you'd likely see total fuel trims 25% or higher. That's where the P0171 came from.

If you have the time, this SD Premium video (for free on YouTube) is excellent study material:

Tyler,

Will check for relearn on the MX808.

Will check for fuel pressure increase with vacuum tube removed.

As I think about all the events that have transpired since that check engine light came on a few weeks ago there are two issues that continue to haunt me. I have been highly trained to do comparison analysis and the use of logic and most of this does not make sense to me.

The RPM issue does not make sense to me for the following reasons:

Why were there no codes thrown during this time? With all the other points the ECM monitors I would reason that the foot throttle angle (sending signal), the throttle body angle (receiver of foot throttle angle) and the actual RPM of the engine would be basically easy to monitor. If the foot throttle was not calling for any increase of engine RPM over idle setting and the throttle body was at an angle that would call for an increase in RPM, this should have sent a code. Based upon the assumption that cruise control was not engaged.

How, why would engaging the transmission into a gear (forward or reverse) cause the idle to increase by two to three hundred RPM?

What condition would cause the throttle body to function properly from time to time?

If you can help me to understand this, it would be greatly appreciated.

Thank you and this site for all of your help.

Bruce

bkreft wrote: Will check for relearn on the MX808

Thanks! I'd also welcome your thoughts on the MX808 as a tool overall. There are some newer technicians I know that are weighing options for an entry level scan tool.

Why were there no codes thrown during this time? With all the other points the ECM monitors I would reason that the foot throttle angle (sending signal), the throttle body angle (receiver of foot throttle angle) and the actual RPM of the engine would be basically easy to monitor...

...

What condition would cause the throttle body to function properly from time to time?

Oh man. :silly: There's no way I can account for all the silly/goofy/backwards reasons OE's do what they do. But I can take a guess!

The best answer I can give you is that your truck has one of the earlier drive-by-wire throttle systems, and it shows. Earlier systems had a different (simpler) throttle body, or just a standard throttle cable. Like the system, the diagnostics and code set criteria are new, and not perfect. I've run into this on GM and other makes. They're slow to set codes. The codes they do set aren't very helpful (as you found out).

Newer systems have had years of refinement on the engineering side, largely driven by OEM's trying to keep warranty times down, IMO. Generalized fault codes can lead to long diagnostic times and parts changing. More specific codes can control that, and thus cost.

How, why would engaging the transmission into a gear (forward or reverse) cause the idle to increase by two to three hundred RPM?

This part isn't that unusual, by itself. The PCM has to open the throttle more when a gear is engaged, to compensate for the additional load on the engine. But in your, it seems like the amount of compensation was off. Like I said, these early systems weren't the best.

Tyler,

You asked for my thoughts on the MX808:

While I am brand new to the Scan world and the art of chasing check engine codes, I am not new to the selection of purchasing of tools. Throughout my career in various trades I have always lived by the creed that good tools are necessary when seeking to do a good job.

Once I had been pushed over the edge and realized that I needed to purchase my own scan tool I began my search by reading comments from other users of various manufacturers. One common theme started to emerge almost immediately and that was Autel. Once I came to this initial conclusion I started to review the various models offered. My focus finally narrowed to the MK808 or the MX808, but I was confused by the similar model numbers and needed some additional information.

I contacted Autel and the person who took my call was very professional and honest, two traits I always admire and look for. The best product in the world is totally useless if you cannot get good support. It was explained to me that the MK model was a Chinese model, whereas the MX model was a USA model. Once I learned this, there was no choice, I ordered the MX808.

Once it arrived and I started the learning curve I was impressed with all the features. What really impressed me was that when I called Autel for some technical support the person who answered the phone not only answered my questions but walked me through some additional features showing me how powerful this tool really was. I am even old school when it came to computers, as I depend solely on workstation computers so using an Android based device was also new to me.

In my opinion this tool will assist the serious technician in performing and delivering a high quality finished product. I highly recommend this scanner for those who do not have a large budget but still want to have a quality tool. The only feature I would like to see would be the ability to attach a keyboard when filling out the forms and other information. My hands and fingers are large and it means I have to use a stylist to enter data which is very slow and tedious from my perspective.

Bruce

Tyler,

Performed a fuel pressure check with vacuum removed as per your request:

Fuel pressure is 54-60 psi with the vacuum line removed.

I feel better about replacing the fuel pressure regulator as previously there was no change with the old regulator.

Bruce

bkreft wrote: Fuel pressure is 54-60 psi with the vacuum line removed.

Nice. Looks good to me.

It was explained to me that the MK model was a Chinese model, whereas the MX model was a USA model. Once I learned this, there was no choice, I ordered the MX808.

Wow. :ohmy: I did NOT know that. Definitely good information for anyone out there considering an Autel.

The only feature I would like to see would be the ability to attach a keyboard when filling out the forms and other information.

I wonder if it'd accept a USB keyboard? :huh: You may have tried this already...