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C5 Gas Gauge finally died.

B/STOCK

Well-known member
Joined
Oct 24, 2001
Messages
187
Location
RI USA
Corvette
2000 Magnetic Red Vert & 2015 DSOM Coupe Z51-3LT

I bought my 2000 new and started to have the gas gauge problem after a few years. Been doing the Techron thing for years but it just doesn't do it anymore. Any ideas on how much to replace the sending unit in the fuel tank or any other magical fixes? I don't mind filling the tank every 100 miles but the check engine and low fuel lights drive me nuts. Sometimes reset shuts them off for a few minutes but that's it. Any idea if it's a big thing to have these two warning light shut down for low fuel? Thanks, Mike
 

Roloman

New member
Joined
Jun 6, 2020
Messages
3
Location
Englewood, Fl 34223
Corvette
03 hot red conv.
Don't give up yet. Try Sea Foam for 7 or 8 fill ups and u will have a shot at correcting the problem.
I had the same problem in my 03.Textron would not work for me. The sending unit in tank could b gummed up.
If that won't work you
have to put a new sending unit in. Expensive propersiton unless u do yourself. If in the gas tank replace fuel
pump also.
 
Joined
Mar 27, 2003
Messages
3,646
Location
Mustang, OK
Corvette
'13 427 60th vert - CTS V Wagon(4-door Vette)
I had good luck with BG 44K fuel system cleaner with my C5s.
You can find it at most NAPA stores.
 

1BAD80

Well-known member
Joined
May 6, 2003
Messages
107
Location
Lapeer,Mi.
Corvette
80 Burgandy Rad.Custom & 2003 Anniversary vert.
I had the same problem on my 03 Chevron gas has the chemical in their gas or use 2 cans Textron (Made by Chevron) to start with gauges started to work after 1/2 tank only one other gas manufacture has it in their gas I think it was Shell , got Textron from O'rileys
next thing to go mite be the EBM anti lock brake module, easy fix for it.
I always run Marvel Mystery Oil in my gas & oil keeps the motor clean inside and works as octane booster, my 80 has 12:1 compression with 92 octane without any knock

Forgot to say Hib Halverson has some good articles
 
Last edited:

Roloman

New member
Joined
Jun 6, 2020
Messages
3
Location
Englewood, Fl 34223
Corvette
03 hot red conv.
I tried Teatron with no luck. When i switched to Sea Foam it took about 4 or 5 times using it but it did the trick.
It use to happen all the time and wouldn't spend the money to have a new sender put in. For 03 owners the fuel pump and sender is in the tanks. If u decide to replace the sender do the fuel pump at the same time. It will save u a headache down the road.
 

BostonED

New member
Joined
Oct 14, 2015
Messages
2
Location
Vista,CA
Corvette
2003 50th Anniversary red, convertible
I have an '03 50th Ann., and have been keeping an eye on the fuel gauge, as it has happened to me also. I stopped for lunch recently, and when I came back in the car the LOW FUEL chime kicked in! WTH? It previously had shown between a 1/4 tank and a 1/2 tank when I first parked. Luckily, the Chevron station was only a three iron away. (ha!) So, $45.00 later with a top off of 91 octane, as seeing as I live in CA (not much longer I hope), and that's the highest octane you can get here, I drove home and added a bottle of Techron that I had in the garage.
This has worked before, but it seems as others have pointed out, to be a temporary fix.
 

grindereleven

Member
Joined
Aug 24, 2016
Messages
12
Location
Michigan's "THUMB"
There has to be something to the Shell fuel "cure". My 2000 never had an issue when using mostly Shell fuel. This Summer I was able to get fuels that begin with the letters "C" and another starting with "S" for quite a bit less, and they were both several miles closer. Now my gauge is having issues. Tried 1 bottle of Techron, going to try another 2 bottles. If no change, will try Seafoam and will go back to Shell.......
 

1BAD80

Well-known member
Joined
May 6, 2003
Messages
107
Location
Lapeer,Mi.
Corvette
80 Burgandy Rad.Custom & 2003 Anniversary vert.
copied from How the C5 fuel tank system works...

C5 Corvette has two fuel tanks, left and right hand. The left hand tank contains the electric fuel pump that supplies fuel to the engine. The right hand tank has a pump, which transfers fuel from the right tank to the left tank. The pump in the right hand tank has no moving parts and is not really a pump. It is a siphon device that uses fuel pressure from the left hand pump to start a siphon that transfers fuel from the right hand tank to the left hand tank. In order to create this siphon, the fuel line that goes to the engine splits and a small amount of pressure is routed to the right hand tank to start the siphoning. The fuel that is being siphoned is routed through another hose to the left hand tank. If the left hand tank is full, the fuel transfers back to the right hand tank through the large filler tube located at the top of the tanks.

The idea is to always keep the left hand tank full whenever there is fuel in the right hand tank. When the fuel gauge reaches a half tank, the right hand tank is empty and the left hand tank is full. Both tanks have a float and sender that measures the fuel level in the tank. These signals go to the Powertrain Control Module (PCM) which interprets the information and sends a signal to the Body Control Module (BCM) which then sends a signal to the fuel gauge in the Instrument Cluster.

Because of the variation in tanks and sending units, the PCM doesn't always read the actual fuel level in the tank. Above or below preset voltage limits, the fuel level is estimated. The voltage limits for each sending unit, right and left, are set to represent "full" and "empty." When one or both tanks have exceeded the preset limits, either "full" or "empty," the system is estimating the actual fuel level. This happens when both tanks are full, gauge is "full;" when the right tank is empty and the left tank is full, "half" on the gauge, or when both tanks are empty, gauge is at "empty."


This estimating strategy and the physical layout of the system results in an unusual fuel gauge characteristic that may be noticeable to some people. When the fuel level is at or near half tank, the right hand tank is empty and the left hand tank is full, so the system is estimating the actual fuel level. Because of the siphoning system, when the car sets without running, the fuel level equalizes in the two tanks. When the car is first started, the system is actually reading the fuel level in both the right and left hand tanks. After running for several minutes, the fuel in the right hand tank has been transferred to the left hand tank, leaving the right hand tank empty and the left hand tank full. The change in the fuel levels results in the system changing from reading the actual fuel level to estimating the fuel level. This change results in the fuel gauge reading actually indicating more fuel than when the car was first started.


One of the common concerns with the Corvette is the fuel gauge goes to "empty" intermittently. First, let's discuss why this happens. As previously mentioned, the system estimates the fuel level at certain times. When the signal from the left hand sender is above the preset voltage limit, the system estimates the left hand tank fuel level to be full. When the signal from the right hand sender is below the preset voltage limit, the computer estimates the right hand tank fuel level to be empty.

In this situation, left tank full and right tank empty, the computer estimates the fuel level and sets that gauge at half tank. Once the fuel level in the left hand tank goes below the preset voltage limit, less than full, the computer begins reading the actual fuel level and setting the gauge accordingly. At this time the computer expects to see the voltage signal from the right hand tank stay below the preset limit that indicates empty. The problem comes from the fact that the signal from the right hand tank does not stay below the preset limit. When the computer sees the right hand signal voltage exceed the preset empty limit, it assumes that there is a problem in the fuel transfer system, which is a possibility. When this condition exists, the computer software turns on the Check Gauges light and commands the fuel gauge to the empty position. The logic for this is, if there were a problem with the fuel transfer system and fuel was not being transferred from the right hand tank into the left hand tank, you could have the gauge indicate half tank, when then the left hand tank would be empty and the right hand tank would be full. In this situation you would run out of gas and be walking.

On some Corvettes the situation that is occurring now is the result of the right hand sending unit being attacked by compounds within reformulated gasoline. This condition manifests itself as an erratic voltage signal from the right hand sending unit. In the above scenario, left tank full and right tank empty, gauge at half, the computer looks for the voltage signal from the right hand tank to stay below a preset level. The erratic voltage signal caused by the reformulated gasoline causes the computer to think there is fuel in the right hand tank when there is not. When this happens the computer software turns on the Check Gauges light and commands the fuel gauge to empty. GM has issued a revised computer software, for 1999 through early 2002 models, that raises the right hand preset voltage empty limit to prevent the erratic voltage signal from causing this situation. While it has proven to be an effective solution, it has not corrected the concern in all instances.

Another possible resolution is to use Techron fuel system cleaner. This has also worked in many, but not all cases.
 

B/STOCK

Well-known member
Joined
Oct 24, 2001
Messages
187
Location
RI USA
Corvette
2000 Magnetic Red Vert & 2015 DSOM Coupe Z51-3LT
There has to be something to the Shell fuel "cure". My 2000 never had an issue when using mostly Shell fuel. This Summer I was able to get fuels that begin with the letters "C" and another starting with "S" for quite a bit less, and they were both several miles closer. Now my gauge is having issues. Tried 1 bottle of Techron, going to try another 2 bottles. If no change, will try Seafoam and will go back to Shell.......
I agree with you on the Shell issue. I had the gague problem 18 years ago and switched to Shell with a bottle of Techron and all was well. One bottle of Techron a year with Shell & all was good till I found myself in the same situation as you, top tier gasoline a little cheaper and closer and the problem came right back. Fixed the problem for now with Techron and Red Line. Nothing else but Shell will ever go in my Corvettes.
 

grindereleven

Member
Joined
Aug 24, 2016
Messages
12
Location
Michigan's "THUMB"
I agree with you on the Shell issue. I had the gague problem 18 years ago and switched to Shell with a bottle of Techron and all was well. One bottle of Techron a year with Shell & all was good till I found myself in the same situation as you, top tier gasoline a little cheaper and closer and the problem came right back. Fixed the problem for now with Techron and Red Line. Nothing else but Shell will ever go in my Corvettes.
Have you ever tried Seafoam? I've used it in other vehicles, but never in my C5, at least not for a gas gauge/sender repair. Reason I ask is I've heard it will often work when Techron will not. Might be worth a try. It is quite a bit pricier, however. What Red Line product did you use with Techron? Inquiring minds want to know!!
 

B/STOCK

Well-known member
Joined
Oct 24, 2001
Messages
187
Location
RI USA
Corvette
2000 Magnetic Red Vert & 2015 DSOM Coupe Z51-3LT
Red Line fuel system cleaner.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19

I bought my 2000 new and started to have the gas gauge problem after a few years. Been doing the Techron thing for years but it just doesn't do it anymore. Any ideas on how much to replace the sending unit in the fuel tank or any other magical fixes? I don't mind filling the tank every 100 miles but the check engine and low fuel lights drive me nuts. Sometimes reset shuts them off for a few minutes but that's it. Any idea if it's a big thing to have these two warning light shut down for low fuel? Thanks, Mike

If you have been using Chevron Techron for a few years, it's unlikely any pour-in additive is going to fix your problem but you can try what I call "the shock treatment".

Buy three bottles of Red Line Complete Fuel System Cleaner and run them though the fuel system one bottler per tankful for three successive fill ups.

If that doesn't fix the issue, you will need to drop one or both of the fuel tanks and replace the sender(s). If the check engine light is on and driving you "nuts", I suggest making the appropriate repairs. That the MIL is on might be because of a fault code relating to the tank sender issue. Fortunately, C5s have on-board capability to display fault codes on the DIC. See the attached .pdf.

Get your codes and post them.
 

Attachments

  • Document ID: 662159.02.pdf
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