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Have a 1998 STS with 104K miles on it. My fuel gauge is pretty much stuck on full after I did some work on the car.

Basically, I filled the tank, drove a few miles, then let the engine cool and changed all 8 plugs to fix an engine misfire I was having. I unscrewed and pushed around the coil pack to get to the back plugs and also changed the air filter while I was at it. That fixed my misfire and the engine is running great.

When I went to drive the car the next few days the fuel gauge needle is stuck on full. My DIC seems to be calculating my range and fuel used accurately. When I accelerate hard or take long sweeping right turns (freeway ramps) the needle will move as much as a quarter tank off full but will then eventually settle back to full. I have driven just over 65 miles now and the needle will settle back to full even after it moves up due to the driving explained above. At engine startup the needle will sweep from empty to full as it should.

I checked my service manuals, but all I could find was sending unit info.

Question: Is there anything in the engine bay that could be dislodged when changing plugs, coil pack removal or air filter change that could cause this? Like a ground wire, fuel rail connection, vacuum line, whatever that has any connection to the fuel gauge?

If not, does this probably mean that my fuel sending unit is cooked and it just coincidentally went haywire after my mini-tuneup? Or is it my float? and if so why is the DIC accurately tracking fuel used and range left?

Any insights/help would be appreciated.

Tom R.

1998 Cadillac STS with 102K Miles

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Would it be unusual for your fuel level to remain on full for the first 65 miles after a fill-up? At freeway speeds my guage stays at or near the full mark for at least 50 to 75 miles depending on how carefully I topped off the tank.

The calculation for fuel used is based on counting fuel injector pulses and pulse width to arrive at the volume of fuel used and therefore fuel remaining.

It might be too soon to condemn the sending unit; see what the guage tells you at the 200 mile mark.

As for dislodging something during a plug change; I doubt it. Pull the codes.


Drive your car.

Use your cell phone.


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Bummer Tomba...

Your fuel sender runs through the Rear Integration Module look for RIM Codes

B0530, B0532 or B0533

BTW whenever the computer triggers one of these codes it sets the gauge to E not F... I guess as an extra encouragement to get the car to the dealer.

Knowing you, you have already done this and you have no codes... this is good

As I read it... Eventually your car will notice that it is using gas and the resistance in the sending unit hasn't changed (amazing cars) and it will trigger a the B0530 code Fuel Sensor Stuck...

This will also set the gauge to the big "E"

You need to test your sender and float.

To do this you need to:

1) Disconnect the fuel level sender connector

2) Connect a 10 watt 40 Ohm resistor (I have one that you can "borrow") to terminals D, CKT 651(BLK/WHT) and terminals A, CKT 30 (PPL).

3) Turn the car on and the tank should read Empty... 250 Ohm = full 40 Ohm = Empty. (if you have a 100 Ohm resistor it will read about 1/2 a tank)

If the gauge reads empty... all of your wiring is OK and you can proceed to replace your sending unit...

PS, and I could be wrong about this, but I believe the car calculated fuel used not from the gauge... but based on the pulse width of the injectors... But don't quote me on that.


Easin' down the highway in a new Cadillac,

I had a fine fox in front, I had three more in the back

ZZTOP, I'm Bad I'm Nationwide


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This is great info Greg. My fuel guage has been acting up lately giving my erratic readings. Where is the fuel level level sensor connect typically located, at the tank? I would like to try this test.

Is it possible to replace the fuel level sensor without replacing the fuel pump?

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I will drive a little further to see if anything changes. Usually at 100km distance I am touching the 1/4 full mark. I don't think that new plugs would have improved my mileage this much. What I find odd is that if the float or sender were toast I would expect the gauge to not move at all - but it does go up to teh 1/4 full mark and back down when I take fast right turns....

I didn't think changing the plugs would have any connection to this, but then again I didn't think my dimming rearview mirror had any connection to the backup lights ground in the trunk - well it did....

Thanks for all the input - I will pull the codes again and see if anything has been trigerred...

Tom R.

1998 Cadillac STS with 102K Miles

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