romandian

the fuel gage on my 99 c5 stoped working. how hard is it to replace?

i could live without the gage but the check gages light is on. is there a way to get rid of the light? i assume idd have to find the correct pins on the bcm and maybe put a resistor accross. has anybody done that? maybe its more complicated that that. could it be the bcm itself?

(btw, the in tank sensors are just fine, i can measure the correct voltage and watch the fuel flowing between tanks when the engine is not running.)

CactusCat

The first thing to do is to see what codes have been thrown. After that, you start tracking down the culprit.
Here's how if you didn't know already.

romandian

sorry, i forgot to mention, no codes (im using efilive).

so, where can i go to find the pinout for the bcm?

romandian

so in the meantime i found out the bcm has nothing to do with it. the two signals go to the ecm (where i logg them) and then to the "dash module" (ipc, whatever it means). the gage itself also seems to be fine as it moves when ignition is switched on. so maybe if im lucky its just a bad connection at the module?

where do i look for the module and has anybody replaced it?

edit: i found this http://corvetteforum.shelor.net/Diag...PC_Pinout.html

and strangely enought i cant see a check gauges pin.

romandian

apparently the ipc module is not a brain controlling the dash but the dash itself (instrument panel cluster). i see it can be pulled out and has some connectors, but you have to remove the top panel. maybe there is an easy way to get at the right connector to check and clean it?

i found some threads on the topic in the meantime but they dont help much. i there really nobody who has done this?

foggy

I would try using Techron Concentrate First.
Get your tank(s) down to 1/8 ish..
Add bottle. Fill . Drive for 1/2 tank or so.
It may require more than one application.
I did this years ago when had issues.
Now I just add techron 3 times a year... Never a problem since

grantv

Along the same lines of what foggy posted...
How full is the tank? Mine will always fail if I fill mine up completely. After the gas goes down to 7/8 or so, it fixes itself (maybe you can guess, I never fill my tank anymore!).
FWIW, I use only 94 octane with Techron no ethanol fuel, have never put a dime in of anything else since I've owned the car.

romandian

well, as i said, the sensors seem to be fine, they logg between 0.7v and 2.3v and behave as expected, unless my notes on this are wrong. can somebody maybe confirm these voltages are correct?

motorboater222

This worked for me on my 2003 Vert by resetting all the codes per this youtube video and adding a bottle of Techron. Super easy not to try it. Good Luck

RedBoy504

I've had my car for 4 years. Fuel gauge has never worked properly. I figured it had to be something major. I've run Techron through it several times only use Chevron premium fuel. Thought I had tried everything. Just went outside in the rain and tried this. Now it works fine. Never even had to start the car. I'm pretty excited. I've run out of gas several times. Not anymore!!!!! Thanks.

aaronc7

Yeah that sounds right/reasonable. I have the same issue, so far no luck running techron or other additives in the fuel. I forget the codes that I get.... 2 codes, 1 per tank/side. When things go wonky voltage reading for both pegs at 5v and stays there.

After the car sits shut down for a while it will be fine. Then about 10 mins into driving, it goes nuts, voltage pegs at 5v, and it doesn't work until it sits again.

It did work flawlessly for about one tank once recently. I filled up at the track with pure gas (no ethanol) and that whole tank worked fine.

romandian

i have no codes, thats the weird part, had it checked by the dealer with the tech 2 also.

im finding diverging info on whether the sensor signals go from pcm to ipc directly or pass through the bcm. does anybody know?

also, what is the third wire for on the sensor connector on the right side? one is the 5v signal that gets pulled to ground by the sensor, second is ground (4 ohms to engine). the third wire has 0.2v on it and is around 14 ohms to ground. any ideas?

btw, i found the right sensor putting out 0.1v more than the left and figured, maybe the pcm didnt like it. so i reduced the voltage from 1.6v to 1.3v by pulling it to ground with a resistor (left being 1.5v). didnt help at all.

other threads:

https://www.corvetteforum.com/forums...ding-unit.html

https://www.corvetteforum.com/forums...nder-says.html

Brad Kirby

If you plan on keeping this car for a while, find a set of factory service manuals for it. It has the diagrams and testing procedures you are looking for.

01pewtervert

Maybe this bulletin will help someone:

Bulletin No.: 02-06-04-010A
Date: June 27, 2003
TECHNICAL
Subject:
Erratic Fuel Gauge Reading (Reprogram the PCM)
Models:
1999-2002 Chevrolet Corvette
Supercede:
This bulletin is being revised to add models and update the Correction and Warranty Information. Please discard Corporate Bulletin Number 02-06-04-010 (Section 06- Engine).

Condition
Some owners may comment about the fuel gauge intermittently indicating an empty reading and then return to the correct fuel level indication.

Cause
This condition may result when fuel blends containing aggressive sulphur compounds react with the fuel sender assembly, which may result in voltage spikes being induced on the fuel level signal to the PCM. Use of another fuel blend may reverse this reaction and return the system to normal operation.

Correction
Reprogram the PCM with the new service calibration which is available in the June 2003, Techline(R) TIS release sent to the dealers on 6/28/03. Use the TIS Version 7 or later data update.

romandian

actually i have copies of the relevant parts of the manual and its pretty useless. it always ends up in telling you to replace the ipc. and i can only repeat, the sensor signals are fine. nothing erratic or intermitent about them.

it would really be interesting to know, if the bcm has anything to do with this.

69

Hello romandian,
Some of the posts that have been linked in this thread for troubleshooting issues are no fully applicable to a 1999 fuel level indication system, (as I was helping/supporting a member with his 1997 model year system which is significantly different than a 1999 system).

I have had reasonable success sorting out CF Members fuel level issues and let’s if we can get your fuel gauge working correctly!
As I review this thread starting from the top, I have the following comments;

Post 3>> “sorry, i forgot to mention, no codes (im using efilive)”.
My comment to post 3> If the car is complete, try to pull the codes from the DIC (do not use EFILIVE) and post up ALL codes logged in the DIC. This step is very important in troubleshooting to ensure there are NO contributing system issues or cascading failure effects impacting the fuel level system. Post up ALL codes to this thread.
NEXT> Clear all codes, and take the car for a 30min drive at various road speeds as we want see if there is a “hard” system failure by pulling the codes from the DIC and post these codes back to this thread for analysis.

Post 8> well, as i said, the sensors seem to be fine, they logg between 0.7v and 2.3v and behave as expected, unless my notes on this are wrong. can somebody maybe confirm these voltages are correct
My comment to post 8> For a model year 1999 fuel level system, the following applies;
Approximate Values
Fuel Level Left Tank voltage Right Tank Voltage
100% 2.5V 2.5V
75% 2.5V 1.5V
50% 2.5V Less than 1V
25% 1.7V Less than 1V
0% Less than 1V Less than 1V

Post 12 My Comment> The info in the first link I posted is only applicable to a 1997/1998 model year car only…The only 1999 data in the thread was the wire schematic labeled in red with “1999”.

Post 15> it would really be interesting to know, if the bcm has anything to do with this.
My Comment Tech Data> Fuel level is read and displayed by the IPC. The IPC obtains fuel level data from the PCM on the serial data line. The IPC only displays the actual fuel level data sent by the PCM; so the PCM is responsible for sending the correct data to the IPC. The IPC will display a LOW FUEL message on the DIC when the IPC receives low fuel data from the PCM. If the IPC cannot receive proper fuel level data from the PCM (due to a communication or sensor malfunction), the IPC will command the fuel gauge to the lowest possible setting.

System Description
There have been past concerns that may result in the PCM commanding the fuel gauge to empty or the vehicle running out of fuel without using all the fuel in the tanks. As solutions have been identified, they have been addressed in service bulletins. Service Manual diagnostics and Service Bulletins should be checked to ensure that the customers concern has been properly diagnosed before any repairs are performed. The vehicle may have a concern of the fuel gauge dropping to empty and DTC P1431 (Fuel Level Sensor 2 Performance) present in Corvette or the vehicle may run out of fuel while still indicating 1/2 tank on the gauge.
The fuel system is designed to use the fuel in the RH (secondary) tank first and then the fuel in the LH (primary) tank. Moving from gage Full to Empty, the RH sender voltage will go from 2.5 volts to 0.7 volts, then the LH sender will go from 2.5 V to 0.7 V. If at any time the RH sender voltage is higher than 0.8 V while the LH is lower than 2.3V, there is probably a jet pump transfer or stuck float issue. The lack of jet transfer could be due to the lack of system pressure or a clogged or inefficient jet pump. This should be determined prior to servicing to avoid replacing the incorrect part. When the fuel gauge is indicating approximately half full/empty or lower, the left hand tank will be full and the right hand tank will be empty under normal operating conditions. When reading the Tech 2 data in the PCM, the sensors must indicate the appropriate fuel level for the PCM to correctly display the actual fuel level accurately.
The following information can be used to diagnose the fuel transfer process which takes place within the fuel system.

Note: The 1997 through 2002 and early built 2003 Corvettes (Starting on November 25, 2002 with vehicle identification number 35111542, all Corvettes use the FFS fuel system) without the FFS system did not have a secondary regulator which prevents the siphoning of fuel (LH to RH) after the vehicle is turned off. The siphoning could balance the fuel such that, at startup, the sender voltages could be similar. That is why there is a 40 minute timer on the P1431 DTC on these vehicles to allow the fuel to transfer to the LH tank after start-up
.
Diagnostic Test Option A:
1. Add enough fuel to ensure fuel gage level is at approximately three quarters (¾) full. 2. With Tech 2, check for and record Diagnostic Trouble Codes (DTCs), and monitor fuel level sensors for both tanks for remainder of procedure. 3. Start vehicle. Run vehicle long enough to confirm RH fuel level decreases while LH remains full (2.5 V).

Diagnostic Test Option B (Draining Fuel):
1. With Tech 2, check for and record Diagnostic Trouble Codes (DTCs) and monitor fuel level sensors for both tanks for remainder of procedure. 2. If RH level is greater than 0.8 V while LH level is less than 2.4 V, there may be a jet transfer issue - continue procedure to confirm issue. 3. Add enough fuel to ensure fuel gage level is approximately three quarters (¾) full. 4. Install Kent-Moore pressure gage/ drain hose to Schrader valve at fuel rail with drain valve closed. 5. Start car and verify pressure is 55-60 psi. If pressure is not at this level correct as necessary. 6. Open drain valve, and drain fuel from rail into empty 5-gallon container. The gage pressure should be @30 psi. 7. Drain fuel. Monitor both level sensors. Drain until RH sensor level drops 0.15V or more. Verify that LH stays at 2.5V while RH decreases. If RH sensor does not move and LH level sensor decreases, increase gage pressure to 55 psi by closing the drain valve. See if RH sensor starts to decrease. If not, there is a jet transfer issue that needs to be resolved. 8. With vehicle/fuel pump still running, close drain valve, and verify system rail pressure returns to 55-60 psi. 9. Shut off vehicle, remove Kent-Moore tool and verify Schrader valve has fully closed. (Key-on vehicle to verify). Replace Schrader cap.
Note: The right side tank sending unit on known good vehicles has shown to be as low as .65 volts while problem vehicles have shown to be above 0.8 volts with the fuel level below a half a tank of fuel (measured).

If the fuel gage is intermittent or dropped to empty due to a fuel system issue, there should be a DTC set.

1997 - 2003 without the FFS system -
1. If the fuel pump does not generate the required pressure (about 52 psi) to run the RH jet pump, the system should be evaluated for internal leaks or faulty regulator(s). The source of an internal leak could be a missing or cut o-ring, a loose connection, or a displaced regulator retaining clip. The fuel feed hose that is installed on the left tank (center hose on the left sending unit) feeds the fuel filter and the orifice hose that goes to the right tank. During assembly the Brown fuel feed hose O-ring may have been cut (this is the 2nd O-ring just inside the hose) and the pieces may have plugged the 0.030 orifice. If this occurs there will be no feed into the right tank and therefore the jet pump will not work and fuel will not return to the left tank.

2. The right side tank fuel sending unit is hanging up for some reason. The float and/or arm may be in contact with something within the tank. This is much less likely on the FFS system. 3. The newest concern relates to the use of reformulated fuels. Many of these fuels have been formulated to reduce their sulfur content. Occasionally, some fuels may contain a small amount of reactive sulfur that attacks the silver tipped sender wiper arm contacts. The silver is being transferred to the card itself resulting in irregular/erratic voltages. While both senders are affected by this concern, it is most likely the right hand sender that sends the incorrect voltage. This occurs because the PCM is expecting to see the voltage signal from the right hand sender remain below 0.7 volts in the empty position. Signals greater than 0.7 volts are not what the PCM expects to see, causing the PCM to command the fuel gauge to the empty position. Replacing the right hand sender will correct this condition until the reactive sulfur attacks the new sender wiper. The time that it takes for this to reoccur can vary anywhere from several days to much longer. The time frame depends on the amount of reactive sulfur in the fuel along with how long the particular tank full of fuel is in the tank. Changing to a different brand of fuel may provide a solution.
Cheers,
Mongoose

romandian

thank you, 69. i pmed chris a few days ago, if he had any insights, as i didnt know the year of his car, but he didnt get back.

in the meantime im aware of everything you wrote. so i can forget about the bcm, cleaning the connector etc. what i still dont get is the third wire on the right sensor connector. third wire from the top looking at the yellow socket. the diagram for year 99 just doesnt make sense:

https://www.corvetteforum.com/forums...ding-unit.html

the voltage splitter with one leg being the sensor. why would that be and how does it work? as mentioned in post #12, i messed around with the sensor. if i pull the signal to ground (top wire) it works as expected, i can adjust it and logg it. i tried to do the same with the third wire, using it as ground (where i get 0.2v and 15 ohms to ground) and weirdly enough the voltage increased. where does that voltage come from? maybe if i understood whats going on there it would help to get rid of the problem.

as mentioned, i had the dealer pull codes with the tech2, all he found was the failed maf (it lives on the shelf). i will indeed try and pull the codes from the dic in a few days, i gave the car away to get inspected in another state.

stingray76l82

I have a 2002 ZO6 that had the same problem. I did the Techron additive work for 1 or 2 fill ups and goes back to empty when I knew I had gas. All the replies you have seen on the board are really good . I took mine to a shop and found out it was the instrument cluster panel. Replaced it have not had a problem since. Just a thought.

69

[QUOTE=
what i still dont get is the third wire on the right sensor connector. third wire from the top looking at the yellow socket. the diagram for year 99 just doesnt make sense:
the voltage splitter with one leg being the sensor. why would that be and how does it work? as mentioned in post #12, i messed around with the sensor. if i pull the signal to ground (top wire) it works as expected, i can adjust it and logg it. i tried to do the same with the third wire, using it as ground (where i get 0.2v and 15 ohms to ground) and weirdly enough the voltage increased. where does that voltage come from? maybe if i understood whats going on there it would help to get rid of the problem.=QUOTE]

Not sure what you mean by the 3rd wire…? Maybe this will clarify.
For a 99’ the Right fuel level sensor plug (wire pin locations) is marked B, C, & D.
For a 99’ wire color codes corresponding to wire pin locations are as follows;
Pin B> Gray Wire Color> Fuel Level Sensor Ground @ PCM
Pin C> Blue Wire Color > 5 Volt Line From PCM
Pin D> Black Wire Color> Fuel Level Sensor “case” ground to Chassis.

Cheers,
Goose

69

More helpful troubleshooting tips,
specifically my post number 18 at this thread.
https://www.corvetteforum.com/forums...h-sensors.html
Cheers,
Goose