1999 Cadillac Deville fuel gauge

08MUSTANG217

MEMBER
1999 CADILLAC DEVILLE
V8
FWD
AUTOMATIC
119,000 MILES

Fuel gauge reads full almost all the time. Drove it, and it went down to 17, then 16, then back up to full. And stayed on full. ALL DATA said take the trunk liner out to get to access panel for fuel pump. Did that, but no such luck. Even tried taking back seat out. No access panel. Started to jack it up to pull the tank, but I thought I'd ask you guys first since most bad fuel senders will make the gauge go to empty. And this is a caddy with 13 on board computers, instead of 7. I know it goes through the rear integration module and the body control module before it goes to the instrument cluster, and at $300.00 for a pump, I thought I'd get another opinion. I'll be glad to donate $10 for a good and definite answer, but not until then.

1 Reply

FACTORYJACK

MECHANIC
4,159 POSTS

The fuel gauge reading from the sender is sent to what is called the PZM, another term for body conrol module. Without a scan tool o read what data is being read by the PZM you are kind of limited. To access the fuel sender on your 99, you do have to lower the tank. I suppose if you access the fuel pump connector, which I believe is at the rear center of the fuel tank(by the rear crossmember), disconnect it and see what the gauge does. If it stays full, that may indicate that open circuit means full. Short the purple and black wire (pins d and f) together with a fused jumper if you have one, and see what the gauge does. It should go full extreme the opposite direction. If open circuit is full, then short circuit would be empty, and vice-versa.