Computer and fuel gauge difference

I noticed that the last two times I filled up that the computer and the fuel gauge are not agreeing. What I mean is, when I usually fill up the gauge goes all the way to the "F" on the gauge and the distance to travel before empty is around 345 miles give or take. What I am getting now is a lower reading on the gauge and about 280 miles to travel before empty. Yesterday I filled up, the tank was at the full mark, not the "F" and it read 275. Today I got in, the gauge was about the same, but the distance to empty was varying between 302 and 285. I must mention that the gas pump is automatically shutting off as usual when filling it up, no, I do not try and add more fuel at that point.

I got a code last week that is popping up on start up, that relates to the fuel tank pressure. This only happens on start up and never when actually traveling down the road. Any clue?

sounds like the EVAP vent valve is sticking. Fairly common on any GM vehicle.

How do you go about fixing it?

you replace it. I do believe there is updated routing for the vent, so not as much crap gets in it.

I'm not trying to be lazy, but I am currently in the military with not a lot of time on my hands. Can you point me in the right direction to accomplish this? Thanks.

The code that comes up is P0452, Evaporative Emission control System Pressure Sensor Low Input. Now when I look it up, it reads " Key on or engine running, then the PCM detected that the Fuel Tank Pressure Sensor signal was less than 0.1v for 5 seconds" Anyone else with this code, what was the fix?

do you have access to a scan tool? That you can watch the parameters?

No, I am using the Torque app.. From what I have read, the sensor is located on top of the fuel pump/sending unit. Unfortunately, the tank is full, so I will have to wait until it gets low to swap it out. I screwed up my shoulder while in AFG last year and still recovering from surgery. I am going home in Oct, and will be going Reserve then. I have a complete shop at my house (PREDATOR-RACING) so I will be able to do the floor board mod then. It just puzzles me as well as others I am sure why it went now. My buddy down here helped me put in a new pump/sending unit a few months ago. This issue just started last week, only at start up. I thought I had read that the 2003 Av sensor was on the fuel rail, must have been a uninformed posting.
Does anyone know how this will effect the vehicle overall? Gas mileage, performance, possible shut down?

AVArookie said:

No, I am using the Torque app.. From what I have read, the sensor is located on top of the fuel pump/sending unit. Unfortunately, the tank is full, so I will have to wait until it gets low to swap it out. I screwed up my shoulder while in AFG last year and still recovering from surgery. I am going home in Oct, and will be going Reserve then. I have a complete shop at my house (PREDATOR-RACING) so I will be able to do the floor board mod then. It just puzzles me as well as others I am sure why it went now. My buddy down here helped me put in a new pump/sending unit a few months ago. This issue just started last week, only at start up. I thought I had read that the 2003 Av sensor was on the fuel rail, must have been a uninformed posting.
Does anyone know how this will effect the vehicle overall? Gas mileage, performance, possible shut down?

Click to expand...

You may be confusing the Fuel Filter on the Frame Rail for the 02 & at least early build 03 model years, with a Fuel Sensor. I don't know where the Fuel Sensor is you've been describing. A Fuel Sensor of sorts did fail or began to throw codes at about 18K miles and was covered easily and quickly repaired/replaced by my dealer. I was under the impression it was near the filler neck and tank entry area. My fix did not require draining the remaining fuel in the tank. If it did, I was not advised of such.

When my dash lit up, I called OnScare and had them advise me of the problem. The soft spoken girl on the other end was doing just fine until she pulled up the script to go with the codes she was seeing.

To paraphrase for what she was saying was along the line of, "Pull over immediately, turn off the engine. Allow us to call GM and have a tow vehicle deliver your Avalanche to the nearest GM Repair facility!" She even included an "Oh Dear, I've never seen this before." Then the script continued with the possibly of Fire, Explosions, complete loss of vehicle control, etc., etc.

I was not aware of any unusual behavior with the vehicle to that point. I finished running my errands and stopped at the dealer an hour later. It was returned in less than 30 minutes. I priced out the parts they used and it was less than $50 back then.

I'm sure there will be a simple fix once you figure out the precise components involved. I'm not a gear head, but I do know where my Fuel Filter was on the Frame Rail each time I replaced it myself. Fuel Sensor, I have no idea.

Welcome Back and take care of the shoulder(s). I've had both repaired and do as much as possible to not repeat the procedure.

It's the fuel tank pressure sensor, it's mounted as I stated above. It costs roughly $35.00 at O'Reillys. The reason for not having a full tank is because of the weight and it is mounted in a lower spot on the tank than the fuel when it is full. From what I have noticed, it doesn't seem to run any different, but not sure what the possibilities are over time.
Thanks for the welcome back, hope you healed well.

I knew it wasn't a large $ cost, but not a job with a bum shoulder either.

Someone will chime in with suggestions or experience for a fix without more damage to the body.

My shoulders are fine now if I stretch before hitting the golf ball. I do have trouble throwing any kind of pitch though.

Stand by, someone will have an answer.

Thanks for the move mod, wasn't sure where to put it.

Just a thought?

The distance is calculated on the ave mpg.....the worse the mpg, the lower the projected distance. Could be a bum flow meter, check by Resetting the ave. mpg readout and check the actual mpg. for the full tank .....possibly the mpg has been going down due to excessive tank pressure in turn increasing the pump pressure forcing you to use more gas and the leaving emissions system to consume the extra fuel.

There is no "flow meter".  Fuel used is determined by the computer knowing how much it wants to use each stroke, which it then translates into how long to fire each injector.  It is not perfect.

Fuel pressure at the injectors should be regulated by the fuel pressure regulator which is mounted up on the engine on the 03s.  I suppose higher than normal fuel pressures in the tank could impede its proper functioning, but I'd say the tank pressure required to do that is highly unlikely.

**Update**
I forgot about the car shop on post. Yesterday, I went up there, used a 90* cut off wheel at low rpm (just slow enough not to throw hardly any sparks at all) and did the floor pan mod to gain access to the top of the tank. (Yes, I could have used a saw or something else that would have been quicker, but I didn't want sparks, flying on to the top of the tank or in my interior, or risk cutting any wires or hoses) I did try to put a piece of lexan on top of the tank, but couldn't get it to the location needed. So, once I cut the access door, I used my LeatherMan file and smoothed all edges. I'll get some primer today and coat all exposed surfaces for future protection. THANKS, to whoever took the time to get the location figured out, I've done this in the past with other vehicles, so attempting didn't bother me much, just seems "natural" to me.

So, I get to O'Reilys, buy the FTHPS and install it in the parking lot, STANDING UP ON THE GROUND! It was like X-mas, I was working on the fuel tank, standing up, with excellent access, by myself, no hoist, in street cloths. SO, far it seems to have fixed the issue. No more light on the dash. I have just about exactly a half tank of fuel, I will fill it all the way up this week and see how it goes....

$40.00 dollar fix, not even breaking a sweat, no tools required for the install, and permanent access to the tank, got to love it.