QuestionI have a 2001 gmc Sierra 1500 4X4 5.3L the gas gauge goes from completely full to completely empty regardless of how much fuel is in the tank. It usually happens when the motor is sitting and idling for 15 seconds or more, and it does it some time while driving too.
AnswerHi
if it does it while siting and or idle, that is a normal condition as per this Official GM bulletin
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
Fuel gauge may be inaccurate or drops to empty (E) and the low fuel light comes on. Further analysis may reveal that this condition is most apparent when the gauge is at or below the quarter (1/4) tank mark.
Recommendation/Instructions:
Try to duplicate the concern by driving the vehicle a short distance in reverse and then stopping (to make fuel slosh), shifting transmission to park or neutral and then shifting to drive. The fuel gauge will have a tendency to read lower than actual. The gauge will take a few minutes to show the actual fuel level. The VCM/PCM is the buffer for the fuel gauge.
On a Automatic Transmission no buffering takes place when the transmission is in park or neutral. This is a NORMAL characteristic & NO repairs are necessary.
On a Manual Transmissions, the fuel gauge is buffered in all gears and neutral. Since the VCM/PCM has no way to know what gear it is in, there is a timer which starts to count up when the clutch is depressed. When this timer reaches its calibrated value (this value will vary), the filtering switches to the "fast" filter (no buffering). When the clutch is releases the filter then switches to the slow filter (system is Buffered). This is a NORMAL characteristic & NO repairs are necessary.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
If it does flucuate from full or while driving steady on smooth road, I would suspect the Fuel level sensor, located inside the tank.
IF you replace the sensor, use a bottle of GM part P/N 88861011 (in Canada, P/N 88861012)
It MAY not be a bad idea to get a bottle of this additive and put it in your tank, as per instructions.
SOMETIMES that will help with the sulphur build up on the sensor circuitry. It does cost between $15.00-$25.00 per bottle, but it would beat the price of the a new tank unit and labor.
Hope this helps
JUST advice from experience
Good luck
Pawl
