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2003 Suburban: Autoenginuity is giving me a P1172 - pump has insuffici


calsdad

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This is happening on a 2003 Chevy Suburban 2500 4x4:

 

I just picked up the Autoenginuity scanner to try and figure out some of the problems I have had with this truck.

 

I've been having an issue with the truck for a number of months - which seems to manifest when I drive it on the highway for a while - at speeds around 70mph.

 

The engine light will light on the dash and I'll see it flicker. Sometimes it will go off on it's own after driving around town.

 

So when I scanned the truck for the first time using Autoenginuity - it said that the truck had a misfire code (forgot the number) - and also a " P1172" code which said " fuel pump insufficient flow".

 

I used Autoenginuity to clear the codes - and the misfire code cleared and did not come back (I've only idled the truck in the driveway since - have not driven it).

 

But the P1172 code still comes back - and I've tried to clear it a number of times.

 

I should also add that the truck does have some sort of leak in the gas tank - when I fill it it up I will get a whiff of gas around the area of the truck. I believe the fuel pump/sender unit may have a some rust thru on it. I've been meaning to pull the tank and change that out - but to avoid the gas smell - I've just been restricting myself to only filling the tank halfway.

 

If there was a vacuum leak in the tank - would that potentially be causing the thing to throw this P1172 code?

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Fuel pump insufficient flow may actually be the source of both your codes. If your truck has an external fuel filter, change it. If you have a fuel leak somewhere, you will be able to see it. Suggest you run the tank to near empty, then drop it down so you can see the entire area around the tank. Fuel leak will leave a stain that does not fade away after it drys. Should be easy to tell where the leak is.

 

Insufficient fuel flow is in regards to the fuel flowing to engine, from the pump. Nothing at all to do with how well the fuel tank is sealed. You very likely have one of two issues, either a plugged fuel filter, or a fuel pump on its way out. If you do not have an external fuel filter, then it will be part of the fuel pump assembly, mounted inside the tank.

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I took a look at AllData last night and paid the $26.95 plus taxes for the manual for my truck. From what I have found so far, it is pretty basic in its language(don't need to be a technician to understand).

 

The navigation process could be done a bit better though. For some items it does not follow the logic I use. I found a couple of places where it offers a procedure for something "without OnStar" and does not then list it "with OnStar". That sort of thing just about always pisses me off. It may simply mean that OnStar does not impact it in any way, so they don't add in the "with OnStar" To me, if it does not matter with or without OnStar, then don't give one option "without Onstar". Just remove the word OnStar from the description.

 

I will look more into it later today and should have a more complete opinion after that.

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Thanks - I'm not sure if there is an external fuel filter or not, I'll have to trace out the fuel line tomorrow and see if there's anything inline between the engine and the tank. I pretty much figured I had to drop the tank sooner or later anyway to try and find the source of the fuel leaking. Now that I know I have the code - I'm going to have to get on that.

 

Could the insufficient fuel flow also have been causing a misfire? When I originally ran the Autoenginuity scan - there was a code about a misfire. I cleared it to see if it would come back , and after running the truck for a half hour or so today - it hasn't reappeared yet. But I haven't yet driven the truck at highway speeds either.

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I took a look at AllData last night and paid the $26.95 plus taxes for the manual for my truck. From what I have found so far, it is pretty basic in its language(don't need to be a technician to understand).

 

The navigation process could be done a bit better though. For some items it does not follow the logic I use. I found a couple of places where it offers a procedure for something "without OnStar" and does not then list it "with OnStar". That sort of thing just about always pisses me off. It may simply mean that OnStar does not impact it in any way, so they don't add in the "with OnStar" To me, if it does not matter with or without OnStar, then don't give one option "without Onstar". Just remove the word OnStar from the description.

 

I will look more into it later today and should have a more complete opinion after that.

 

 

 

 

I signed up for the Alldata personal one vehicle option also.

 

For this P1172 code - it seems to be indicating that the second tank's transfer pump is having an issue:

 

----------------------------------------------

 

CIRCUIT DESCRIPTION

The secondary fuel pump is located in the rear fuel tank. The secondary fuel pump is powered by a secondary fuel pump relay. Fuel is transferred from the rear fuel tank to the front fuel tank in order to ensure all of the usable fuel volume is available to the primary fuel pump. The secondary fuel pump relay supply voltage is received from the primary fuel pump relay when the primary fuel pump is energized. The secondary fuel pump relay ground is controlled by the powertrain control module (PCM). The secondary fuel pump diagnostic runs only at idle. If the PCM commands the secondary fuel pump ON and a predetermined change in both the front and rear fuel level sensors does not occur, DTC 1172 sets.

 

CONDITIONS FOR RUNNING THE DTC

  • DTCs P0461, P0462, P0463, P1431, P1432, P1433 are not set.
  • The vehicle speed is 0 km/h (0 mph) .
  • The engine has been idling for more than 2 minutes and 20 seconds .
  • The primary fuel level is less than 60 L (15.8 gal) .
  • The secondary fuel level is more than 3 L (2.6 gal) .

CONDITIONS FOR SETTING THE DTC

The PCM does not detect a change of 4 L (1.06 gal) in both the primary and secondary fuel level sensors with the secondary pump commanded ON for 120 seconds .

 

-----------------------------------------------------------------------------

 

 

This truck has had some sort of leak from the gas tank for a while. So for probably a couple of years now I've only been filling to about half full to avoid the leaking issue. It's something I've got to fix - it's on the list.

 

Could the second tank's transfer pump have gone bad from not being used for a while?

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To me, yes the insufficient fuel flow could cause the misfire message. I would expect it to happen at higher engine speeds, like in highway driving.

 

I came across something interesting tonight while looking into 302 Ford tunnel port engines. There was a comment by a reader regarding to the newer fuels we have with ethanol will sometimes give off a fuel smell due to the smaller molecules of the new fuels vapours passing through some of the older fuel lines. This will not leak fluid, just fumes. This type of condition will not leave a stain behind. Don't know for sure if this is what you are experiencing, but it is something to consider. This would apply to all non-metal parts of the fuel system near the tank, like the o-ring that seals the sender to the tank, the fuel fill line, etc.

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This is happening on a 2003 Chevy Suburban 2500 4x4:

 

I just picked up the Autoenginuity scanner to try and figure out some of the problems I have had with this truck.

 

I've been having an issue with the truck for a number of months - which seems to manifest when I drive it on the highway for a while - at speeds around 70mph.

 

The engine light will light on the dash and I'll see it flicker. Sometimes it will go off on it's own after driving around town.

 

So when I scanned the truck for the first time using Autoenginuity - it said that the truck had a misfire code (forgot the number) - and also a " P1172" code which said " fuel pump insufficient flow".

 

I used Autoenginuity to clear the codes - and the misfire code cleared and did not come back (I've only idled the truck in the driveway since - have not driven it).

 

But the P1172 code still comes back - and I've tried to clear it a number of times.

 

I should also add that the truck does have some sort of leak in the gas tank - when I fill it it up I will get a whiff of gas around the area of the truck. I believe the fuel pump/sender unit may have a some rust thru on it. I've been meaning to pull the tank and change that out - but to avoid the gas smell - I've just been restricting myself to only filling the tank halfway.

 

If there was a vacuum leak in the tank - would that potentially be causing the thing to throw this P1172 code?

There is a chart to diagnose the code ... When you buy service information from alldata. Com .$30. /yr

 

No brainer ,,,, don't guess at anything .... Do it right

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Since you never mentioned in the first post that you had two fuel tanks, I just assumed you only had one. Have you put fuel into the second tank? What is the level in that tank? Perhaps the leak you have is between the two tanks?

 

Are two tanks treated like they always were? Used to be having two fuel tanks acted just like you had two tanks. They were two independent fuel storage devices that you would switch between with a switch on the dash, or one on the floor. Gas gauge would switch to the tank you selected with the switch, as would the fuel supply. The quoted text above reads like the second tank is more like a spare gas can that will pump its contents into the main tank as needed.

 

From how I read the text, if the rear fuel tank in empty, it will set that code since it cannot possibly pump one gallon of fuel from the rear tank to the front tank in 120 seconds. The misfiring has nothing to do with this issue. That is something different. Fix the fuel issue first though. Perhaps the rear tank is leaking?

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Since you never mentioned in the first post that you had two fuel tanks, I just assumed you only had one. Have you put fuel into the second tank? What is the level in that tank? Perhaps the leak you have is between the two tanks?

 

Are two tanks treated like they always were? Used to be having two fuel tanks acted just like you had two tanks. They were two independent fuel storage devices that you would switch between with a switch on the dash, or one on the floor. Gas gauge would switch to the tank you selected with the switch, as would the fuel supply. The quoted text above reads like the second tank is more like a spare gas can that will pump its contents into the main tank as needed.

 

From how I read the text, if the rear fuel tank in empty, it will set that code since it cannot possibly pump one gallon of fuel from the rear tank to the front tank in 120 seconds. The misfiring has nothing to do with this issue. That is something different. Fix the fuel issue first though. Perhaps the rear tank is leaking?

 

I can't say I completely understand how the dual tank system works - but here is my current understanding:

 

There's a "main" tank that is located on the driver's side alongside the frame rail , it's approximately under the 2nd row seat - in front of the rear axle. That tank holds approximately 25-28 gallons. Then there's a second tank - that is located right under the spare tire (above the spare tire actually). That tank holds the rest - and I believe the total capacity is something like 35 - 37 gallons.

 

There is a hose - looks like a radiator hose - that runs from the main tank to the secondary tank. I believe that hose is so that both tanks can be filled. There is only one fuel fill (located on the side of the truck).

 

My understanding is that there is a pump in each tank - and a fuel level sender. The main tank pump feeds the engine and then the secondary tank's pump basically just feeds the main tank. The computer somehow understands that there are two senders and controls the secondary pump and what the fuel level gauge reads based on those senders.

 

This two tank system is standard I believe on the GMT800 and GMT900 Suburbans. My understanding is that the only other Chevy trucks that have a dual tank system are some of the cab and chassis trucks. The guys who are doing diesel conversion on Suburbans have to deal with this because the diesel Silverados don't come with the dual tanks - so they've got to do custom programming to get the Suburban with the diesel to work with the dual tanks.

 

Once I get thru some of the other issues the truck has - I've got to take a closer look at where exactly the leak is coming from the tank system. It could be coming from the hose - but I just don't know. Normally I only drive the truck locally so I just dealt with it by only filling the tank level to half-way.

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Chances are the manual you just signed up for will tell you how it is setup. Unless there is a pump that runs while you are filling the tank, the only way you can fill both tanks is if the hose between the two tanks is at a level that allows gravity to fill the rear tank from the front tank while at the gas pumps. Otherwise there must be a pump that transfers the fuel to the second tank while filling the truck up. Having it pump after you have left the station would not give your max fuel capacity.

 

The error that is being set means that either the front or the rear tank fuel level sensor is not measuring a change in level. You will need to get a better understanding of how the fuel is transferred when filling the tank at a gas station. The leak may very well be the transfer line or the seal on the fuel pump/level sensor in the rear tank.

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There is a chart to diagnose the code ... When you buy service information from alldata. Com .$30. /yr

 

No brainer ,,,, don't guess at anything .... Do it right

 

Thanks - I'll check out Alldata. For $30.00 a year it might be worth it.

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Chances are the manual you just signed up for will tell you how it is setup. Unless there is a pump that runs while you are filling the tank, the only way you can fill both tanks is if the hose between the two tanks is at a level that allows gravity to fill the rear tank from the front tank while at the gas pumps. Otherwise there must be a pump that transfers the fuel to the second tank while filling the truck up. Having it pump after you have left the station would not give your max fuel capacity.

 

The error that is being set means that either the front or the rear tank fuel level sensor is not measuring a change in level. You will need to get a better understanding of how the fuel is transferred when filling the tank at a gas station. The leak may very well be the transfer line or the seal on the fuel pump/level sensor in the rear tank.

 

 

I'll have to check that out a little more (Alldata).

 

I'm pretty sure the large hose is located near the top of the two tanks - so once the level in the main tank gets high enough, it fills the secondary tank. Then the pump in the secondary tank runs just to put the fuel back into the main tank.

 

Based on your description - I suppose the error message makes sense. I have probably not filled the overall fuel level on the truck past the 1/2 level in a couple of years. The computer may be interpreting the fact that the secondary tank has been empty for so long - as an error.

 

I'll just sit on the error for now and look closer into fixing the leak - and then fill the tanks up to completely full (once I figure out where the leak is coming from) - and see if the error still persists.

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I'm pretty sure the large hose is located near the top of the two tanks - so once the level in the main tank gets high enough, it fills the secondary tank. Then the pump in the secondary tank runs just to put the fuel back into the main tank.

 

That actually sounds like it would be that way. It would use gravity and the gas pump at the station to fill the rear tank, and once you have used up about a quarter tank it would use the pump in the rear tank to equalize the front tank. GM could have saved some money and technology by just putting a line at the bottom of the rear tank and run it into the front tank as well. Would not even need the upper hose. As long as the lower hose on rear tank was higher than the spot it connects to front tank. They would also need to run a vent line from top of rear tank to top of front tank to equalize pressures and prevent an air lock.

 

If you can gather up a bunch of 5 gallon gas cans you can use them to fill the last half of the tank to find the leak, then siphon the fuel out back into the 5 gallon cans to stop the leak. Were it me, I would make this the most important fix, sometimes fuel leaks all of a sudden get worse.

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That actually sounds like it would be that way. It would use gravity and the gas pump at the station to fill the rear tank, and once you have used up about a quarter tank it would use the pump in the rear tank to equalize the front tank. GM could have saved some money and technology by just putting a line at the bottom of the rear tank and run it into the front tank as well. Would not even need the upper hose. As long as the lower hose on rear tank was higher than the spot it connects to front tank. They would also need to run a vent line from top of rear tank to top of front tank to equalize pressures and prevent an air lock.

 

If you can gather up a bunch of 5 gallon gas cans you can use them to fill the last half of the tank to find the leak, then siphon the fuel out back into the 5 gallon cans to stop the leak. Were it me, I would make this the most important fix, sometimes fuel leaks all of a sudden get worse.

 

 

Thats not a bad idea. I already have a bunch of 5 gallon cans. I could fill up the Suburban - wait for the leak to manifest - and then transfer a bunch of gas into my other vehicles.

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So http://www.alldatadiy.com/buy/ lists the one year for one car at $26.95.

 

The Alldata.com site looks like it's for "professionals" - is there any difference in the info you can get out of the different options?

I haven't used alldata for at least 7 yrs so I can't answer your question .

 

It's not meant for just pros , anyone can buy it ,and a second veh for $14 I believe !!

 

It is a no brainer for sure , no guessing , the info is there , if you get to a step that you can't do because of a tool or something then your screwed .

 

It's getting harder and harder for shade tree home repairs and will only get worst I'm afraid ....cuz 10 computers in a vehicle is just not enough lol

 

Have a good day !!

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