I would speculate it is the sender, it is more probable than the PZM(body control module), although that is another player in the game. What was his diagnosis to determine it is the BCM? There is this bulletin on the sender, pasted for your review;
#83-83-10A: FUEL GAUGE FLUCTUATES BETWEEN FULL AND EMPTY - (Sep 17, 1998)
REVISION: 09/16/98 DIVS INVL 3 4 6 7
THIS BULLETIN IS BEING REVISED TO CHANGE MODEL INFORMATION, REPAIR PROCEDURE AND ADD PART AND LABOR TIME INFORMATION. PLEASE DISCARD CORPORATE BULLETIN NUMBER 83-83-10 (SECTION 8 - CHASSIS/BODY ELECTRICAL) ______________________________________________________________________
SUBJECT: FUEL GAUGE FLUCTUATES BETWEEN FULL AND EMPTY WHEN TANK IS FULL (INSTALL FUEL LEVEL SENSOR KIT)
MODELS: 1998 BUICK PARK AVENUE 1998 CADILLAC DEVILLE, ELDORADO, SEVILLE 1998 OLDSMOBILE AURORA
SOME CUSTOMERS MAY COMMENT ABOUT THE FOLLOWING -
1. THE FUEL GAUGE READS EMPTY WHEN TANK IS FULL; AND/OR
2. THE FUEL GAUGE FLUCTUATES BETWEEN FULL AND EMPTY WHEN TANK IS FULL.
THIS CONDITION MAY BE DUE TO CONTAMINATION BUILD UP IN THE RESISTIVE INK OF THE FUEL SENDER ASSEMBLY'S FUEL LEVEL SENSOR CERAMIC CARD.
REPLACE THE FUEL LEVEL SENSOR IN THE FUEL SENDER ASSEMBLY.
Friday, March 12th, 2010 AT 11:43 PM