Fuel Level Indication Problems and Repairs

Introduction

Fuel level indication problems are generally caused by a fault with either the gauge or the sending unit. This procedure covers isolating the cause and the corrective steps for each.

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Checking for Proper Gauge Operation

Tools

• Multimeter
• Test leads
• Variable potentiometer

Sender Resistance vs. Indicated Level

Model years 1977–1985:

Level	Resistance (Ohms)
RESERVE	71.6
1/4	58.7
1/2	34.5
3/4	15.3
FULL (1/1)	3.2

Model years 1985.5–1995:

Level	Resistance (Ohms)
RESERVE	63.2
1/4	42.2
1/2	21.2
3/4	8.6
FULL (1/1)	2.8

Procedure

1. Remove the carpet from the rear hatch area.

2. Remove the fuel sender cover (typically covered by an insulation pad).

3. Disconnect the electrical connector from the top of the fuel level sender.

4. Set the variable potentiometer to one of the resistance values from the table appropriate for your model year.

5. Connect the potentiometer between Terminals 1 and 3 on the disconnected connector. On some cars, Terminal 1 may be labelled "G" and Terminal 3 may be labelled "31" or "T". Ensure no wires contact the body or fuel tank where they could be grounded unintentionally.

6. Turn the ignition to ON.

7. Check the fuel level gauge — it should indicate approximately the level corresponding to the installed resistance.

8. Turn the ignition to OFF.

9. Remove the installed resistance.

10. Repeat steps 4–8 for several resistance values across the full range.

Results

If the gauge indication does not match the expected level, the problem is in the wiring between sender and gauge, or the gauge itself.

If the gauge circuit is suspected, first clean the fuel sender grounds:

• Early 944s (pre-1985.5): Grounding point is in the rear hatch area near the left rear light.
• Late model 944s: Grounding point is on the inside of the firewall, driver's side (LHD).

Also clean the electrical connections at the gauge. On 1985.5 and newer cars with instrument clusters, remove the gauge package per ELECT-07 and clean the ribbon connectors on the back using a pencil eraser. On early cars, remove the gauges per ELECT-06 and clean the contacts for the fuel level gauge.

If problems persist after cleaning, the gauge cluster (or early-model fuel pressure gauge) can be sent to an authorized VDO repair facility for testing.

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Fuel Level Sender

If gauge testing indicates the gauge is operating correctly, the problem is most likely the fuel level sender. Gumming of the sender mechanism is common and cleaning often resolves the problem.

Procedure

1. Disconnect the electrical connector for the sending unit.

2. Disconnect the two fuel lines on top of the tank.

3. On 1985.5 and newer cars: Turn the black plastic locking ring counter-clockwise to release the sender.

4. On pre-1985.5 cars: Remove the five cheesehead screws holding the sender to the top of the fuel tank.

5. Lift the fuel sending unit out of the top of the fuel tank.

6. Thoroughly clean the sender float and slide mechanism using engine degreaser or carburetor/choke cleaner and a brush.

7. Connect an ohmmeter between terminals 1 and 3 on the sender.

8. With the float all the way down, resistance should read approximately the RESERVE value for your model year (see table above).

9. Slowly raise the float while watching the resistance reading. Resistance should decrease smoothly and steadily to approximately 3 Ω at full float-up.

10. The decrease in resistance should be linear and smooth. Erratic resistance changes indicate the sender is faulty or requires additional cleaning.

11. If satisfactory readings cannot be obtained, replace the sender.