Fuel Tank Sending Unit - Diagnosis: Overview
Group: 20Number: 98-01
Date: Sept. 21, 1998
Subject:
Fuel Tank Sending Unit, Diagnosis
Model(s):
A6 Sedan with (All Wheel Drive) 1998-->
A6 Avant with (All Wheel Drive) 1999-->
Condition
Incorrect fuel reading on fuel gauge (erratic).
May be caused by a fault in one of the three fuel tank sending units.
Service
The following overview of the fuel tank sending unit system is provided to gain a better understanding of how the system works.
Determination of fill volume
Within the complex geometry of the fuel tank, three fuel gauge tank sending units are used to signal the fuel level in the tank.
^ One or more of the senders for the fuel gauge operate, depending on how full the fuel tank is.
^ The three senders for the fuel gauge are connected in series. The individual resistances of the senders are added together to get a "total resistance".
^ A microprocessor in the multipurpose instrument panel insert, processes this data.
Electrical Circuit
-G- Sender for fuel gauge
-G1- Fuel gauge
-G169- Sender II for fuel gauge
-G237- Sender III for fuel gauge
Sending unit location
Note:
The lower sending units -0- and -G169- are accessible through openings under the rear bench seat cushion.
The upper sending unit -G237- is accessible through an opening in the luggage compartment.
Note:
^ Due to the various locations of the sending units, checking can only be done when the tank is either empty or full.
^ The sending units are connected in series. Therefore, to ensure correct readings, always remove the harness connectors at all the sending units before performing the following measurements (See Sending Units, Checking).
Diagnosis (includes checking full and empty, does not include Labor Operation 2015712):
When diagnosis procedure applies to vehicles within the New Vehicle Limited Warranty, use the following:
Part Identifier: 2015
Labor Operation: 2015711 115TU
Sending Unit replacement (does not include Labor Operation 2015711):
When procedure applies to vehicles within the New Vehicle Limited Warranty, use the following:
Part Identifier: 2015
Labor Operation 2015712 30TU
Replace one or all