Help, just bought my first C5 Corvette, and on long drive home the "Gage check" warning light came on, fuel gauge went to zero & subsequent "Low Fuel" warning text came up....had covered approx 50miles. Stopped at next services, switched off, used the rest room, came back, started up and all warnings gone & fuel gauge restored to normal...then about another 100miles does the same thing...any help would be appreciated on this...
Gage/Gauge check warning light
- Thread starter Kingqa69
- Start date
Mr. Cricket
Committee Member
Congrats on buying your first Corvette and joining our club. Had 2 C5's back in the day and what great cars they are.
For my money they're the best value Corvette you can get.
Thanks..any ideas whereabouts the sender is fitted in the tank?
teamzr1
Supporting vendor
The 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 an issue 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 Ethanol 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.
Later it was found the GM fixes did not solve the problem but rather the use of Ethanol (E10) gas
Another possible resolution is to use Techron fuel system cleaner. This has also worked in many, but not all cases.
Photos when I repaired this on my 1999 C5
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 an issue 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 Ethanol 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.
Later it was found the GM fixes did not solve the problem but rather the use of Ethanol (E10) gas
Another possible resolution is to use Techron fuel system cleaner. This has also worked in many, but not all cases.
Photos when I repaired this on my 1999 C5
teamzr1
Supporting vendor
Operation of a typical in-tank fuel level sending unit is based on variable resistance. As
the float moves up or down according to fuel level, the resistance in the sending unit varies.
This varying resistance is processed by the engine control module (ECM) and the resulting information is sent to the instrument panel cluster (IPC) for display on the fuel gauge.
In the past, the sending unit was set up so that high resistance indicated high fuel level, and low resistance indicated low fuel level.
Sulfur contaminants found in some of today's gasoline can form deposits on the sending unit, resulting in higher-than-intended resistance.
The high resistance from the deposits could be misinterpreted as a high fuel level, when in fact the fuel level is low.
The driver may run out of fuel, even though the fuel gauge is not indicating low or empty.
To offset this effect, engineering has begun "flipping" fuel senders, reversing the circuitry.
This means that high resistance now indicates low fuel level and low resistance indicates high fuel level.
So, if deposit build-up adds to sender resistance, the gauge will err in the direction of indicating less fuel than is actually in the tank.
The "flipping" process began in the 2004 model year, continued through model years 2005-06.
The remaining vehicles will have their fuel level sending units "flipped" for the 2007 model year.
TIP: When diagnosing fuel sender operation, it's critical to refer to the appropriate model year information in SI, to be sure which resistance specifications apply.
TIP:
GMSPO offers GM Fuel System Treatment PLUS p/n 88861011 (88861012 in Canada) which helps protect fuel sending units from contaminating deposits.
the float moves up or down according to fuel level, the resistance in the sending unit varies.
This varying resistance is processed by the engine control module (ECM) and the resulting information is sent to the instrument panel cluster (IPC) for display on the fuel gauge.
In the past, the sending unit was set up so that high resistance indicated high fuel level, and low resistance indicated low fuel level.
Sulfur contaminants found in some of today's gasoline can form deposits on the sending unit, resulting in higher-than-intended resistance.
The high resistance from the deposits could be misinterpreted as a high fuel level, when in fact the fuel level is low.
The driver may run out of fuel, even though the fuel gauge is not indicating low or empty.
To offset this effect, engineering has begun "flipping" fuel senders, reversing the circuitry.
This means that high resistance now indicates low fuel level and low resistance indicates high fuel level.
So, if deposit build-up adds to sender resistance, the gauge will err in the direction of indicating less fuel than is actually in the tank.
The "flipping" process began in the 2004 model year, continued through model years 2005-06.
The remaining vehicles will have their fuel level sending units "flipped" for the 2007 model year.
TIP: When diagnosing fuel sender operation, it's critical to refer to the appropriate model year information in SI, to be sure which resistance specifications apply.
TIP:
GMSPO offers GM Fuel System Treatment PLUS p/n 88861011 (88861012 in Canada) which helps protect fuel sending units from contaminating deposits.
oelarse
Well-known user
I advice to get someone to view the sender voltage values and DTC codes view a Tech2 or similar scanner .
If the siphron pump in the passenger side is clogged the fuel will not move from passenger to driverside .
The signal on the passenger side shall drop first and when the passenger side is empty the driverside wil start to drop IF everthing is working properly.
This should be done before opening/inspecting any fuel senders
Both senders shall change resistance from 50 to 250 ohm without any drop if the sender slipring is ok when moving the sender arm from empty to full tank
If the siphron pump in the passenger side is clogged the fuel will not move from passenger to driverside .
The signal on the passenger side shall drop first and when the passenger side is empty the driverside wil start to drop IF everthing is working properly.
This should be done before opening/inspecting any fuel senders
Both senders shall change resistance from 50 to 250 ohm without any drop if the sender slipring is ok when moving the sender arm from empty to full tank
Thanks for the really good info.I advice to get someone to view the sender voltage values and DTC codes view a Tech2 or similar scanner .
If the siphron pump in the passenger side is clogged the fuel will not move from passenger to driverside .
The signal on the passenger side shall drop first and when the passenger side is empty the driverside wil start to drop IF everthing is working properly.
This should be done before opening/inspecting any fuel senders
Both senders shall change resistance from 50 to 250 ohm without any drop if the sender slipring is ok when moving the sender arm from empty to full tank
View attachment 28682View attachment 28683View attachment 28684
teamzr1
Supporting vendor
The fact is if the car still functions it still is getting gas from the tanks
If the transfer tube between the 2 tanks was the issue and gas gauge reporting no fuel of course than
engine would not run
What I posted above was from GM, and was so bad the recall and TSB changed to all model years of the C5 due to the damage done by the Ethanol
GM TSB is 02-06-04-010A which I attached below to this post as a PDF
OP needs to go to someone that has a GM Tech-II and query the PCM and see if the TSB was done or not
If not have them apply that fix, if it was done than the ethanol has done too much damage and float senders need replacement
The PCM has 8 software code segments as I show below, one is for the fuel system and has a version number I show
The Tech II would show those segments and could see if the TSB for this issue was updated into the PCM
If the OP posts the VIN # of his C5 (who has not posted what year it is)
I could query the GM server, which would report all TSB assigned against that C5s PCM
I suggest if the OP has someone use a Tech-II is to do ALL TSB / code segment updates as other GM issues
they corrected, including the no start issue to the steering column lock failures the updates solves
If the transfer tube between the 2 tanks was the issue and gas gauge reporting no fuel of course than
engine would not run
What I posted above was from GM, and was so bad the recall and TSB changed to all model years of the C5 due to the damage done by the Ethanol
GM TSB is 02-06-04-010A which I attached below to this post as a PDF
OP needs to go to someone that has a GM Tech-II and query the PCM and see if the TSB was done or not
If not have them apply that fix, if it was done than the ethanol has done too much damage and float senders need replacement
The PCM has 8 software code segments as I show below, one is for the fuel system and has a version number I show
The Tech II would show those segments and could see if the TSB for this issue was updated into the PCM
If the OP posts the VIN # of his C5 (who has not posted what year it is)
I could query the GM server, which would report all TSB assigned against that C5s PCM
I suggest if the OP has someone use a Tech-II is to do ALL TSB / code segment updates as other GM issues
they corrected, including the no start issue to the steering column lock failures the updates solves
teamzr1
Supporting vendor
What is the VIN # so I can check GM if your '99 was assigned for this TSB to be done ?
teamzr1
Supporting vendor
Here you go from GM's history for your 1999 C5 as to its VIN #
You notice there are two updates related to fuel system functions
The main OS has a fix for one condition that causes fuel problems
Then you see another fuel system TSB fix, this relates to problems due to use of Ethanol
At this time, you do not know if any or part of these updates were even done in the past
Someone with either a Tech II, a clone one or a PCM tuning tool needs to read the PCM code segments and there part numbers
The newer the update is, the larger the number is
You compare the part numbers of yours and then compare the numbers with this list to determine if the update was done or not
You also then see what they state the update purpose was
I would first do the updates and see if that helps the fuel gauge issues before starting to considering taking fuel tanks repairs
Print this out so you can compare your PCMs part #s to the updates GM has on file for your C5
Again have all the segment updates done as to the reasons GM came up with these updates for the PCM
You notice there are two updates related to fuel system functions
The main OS has a fix for one condition that causes fuel problems
Then you see another fuel system TSB fix, this relates to problems due to use of Ethanol
At this time, you do not know if any or part of these updates were even done in the past
Someone with either a Tech II, a clone one or a PCM tuning tool needs to read the PCM code segments and there part numbers
The newer the update is, the larger the number is
You compare the part numbers of yours and then compare the numbers with this list to determine if the update was done or not
You also then see what they state the update purpose was
I would first do the updates and see if that helps the fuel gauge issues before starting to considering taking fuel tanks repairs
Print this out so you can compare your PCMs part #s to the updates GM has on file for your C5
Again have all the segment updates done as to the reasons GM came up with these updates for the PCM
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