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Fuel Level Sender Replacement
 
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Pelican Technical Article:

Fuel Level Sender Replacement

Tom Morr

Time:

1 hour1 hr

Tab:

$500

Talent:

**

Tools:

Flat head screwdriver, 10mm socket, ratchet, extension, pin removal tool

Applicable Models:

Mercedes-Benz SLK230 (1998-04)

Parts Required:

Replacement fuel level sender, O-ring seal

Hot Tip:

Draining the fuel tank minimizes the possibility of dripping fuel in the trunk.

Performance Gain:

Restores accuracy to the fuel gauge.

Complementary Modification:

Replace the fuel filter while the tank is empty.

Inaccurate fuel gauges are annoying at best and if not corrected can leave you stranded at the side of the road.

Unfortunately, the sender's rheostat/potentiometer wears out over time as the float's arm sweeps over it. Mercedes-Benz even issued a TSB on this in 2002. Thereafter, fuel senders were upgraded by adding gold to the contact fingers to improve the signal to the fuel gauge. While there have been many DIY attempts to fix a faulty or wearing fuel level sender most have not had any positive lasting results. If your sender is going bad it is best to just replace the unit.

The good news is that the job isn't tough. The sender is located in the fuel tank and the fuel tank is readily accessible in the trunk. The trunk's vertical liner panel removes easily enough, allowing access to the fuel level sender. Cleaning out the trunk will likely take longer than removing the trim panel.

The main challenge is removing the old sender. It's plastic and uses a bayonet-style mount with two round holes. A special pin tool is made specifically for the job, but DIYers often find their own solutions. Large channel locks is one.

We took a flat bar of steel and drilled two holes to align with the sender's bayonet sockets: about 2-3/8 inches / 60mm apart. Various sized bolts were tried until ones that threaded themselves into the plastic sockets were chosen (6mm bolts borrowed from the trunk-mounted CD changer's mounting bracket). Making the tool was the most time-consuming part of the job and still only took about 45 minutes.

Twisting the sender a few degrees counter-clockwise from its locked 12 o'clock and 6 o'clock position to 11:00/5:00 releases the unit. The amount of force required depends on how bonded the O-ring seal is to the fuel tank.

Some tips; Potential for fire is always a concern when working on fuel systems. Disconnect the battery's negative cable to minimize possibilities of sparks. Work in a well-ventilated area away from open flame. Always keep a Class B fire extinguisher within arm's reach. If possible, drain the fuel tank or siphon out as much fuel as feasible to minimize mess in the trunk. At a minimum, the tank should be at least 2 gallons (8L) below full so fuel won't slosh out. Capture gas in an appropriate container. Relieve pressure from the fuel system at the fuel rail's Schrader valve. Capture any fuel with rags and an appropriate container. Tape off the tank's opening if the new sender isn't installed immediately. This obviously keeps dirt from entering the tank. Lubricating the O-ring seal with a light coat of oil eases installation and future fuel-sender replacement. Make sure the sensor wires are clear of the tank's hole before inserting the new fuel level sender.

Installation is the reverse of removal

The less fuel in the tank, the cleaner the job.
Figure 1

The less fuel in the tank, the cleaner the job. Fuel pressure is released at the fuel rail's Schrader valve, protected by a 15mm gold nut.

The upper trim panel must be removed to access the fuel tank.
Figure 2

The upper trim panel must be removed to access the fuel tank. The panel is secured on top by two 10mm flange nuts: one at the arrow, the second in the nut driver.

The plastic side panels top upper-most push clips (green arrows) are removed by first popping out the center buttons with a flat head screwdriver, then gently lifting the clips' sockets out of the hole in the sheet metal.
Figure 3

The plastic side panels top upper-most push clips (green arrows) are removed by first popping out the center buttons with a flat head screwdriver, then gently lifting the clips' sockets out of the hole in the sheet metal.

The trunk blind come out by removing two 10mm bolts (green arrows).
Figure 4

The trunk blind come out by removing two 10mm bolts (green arrows).

After the trunk blind is removed, the upper trim panel can be shimming out from under the trunk's side panels and set aside.
Figure 5

After the trunk blind is removed, the upper trim panel can be shimming out from under the trunk's side panels and set aside.

The tank and fuel level sender are now accessible.
Figure 6

The tank and fuel level sender are now accessible. Connectors for the fuel gauge sensor and pressure sensor can be unplugged. The sender has gray bayonet sockets at 12 o'clock and 6 o'clock.

Special pin tools are available for removing the sender.
Figure 7

Special pin tools are available for removing the sender. We made a makeshift one by drilling holes in a piece of flat-stock metal and using two 6mm bolts to catch the sockets. Some elbow grease was necessary to break the O-ring seal from the tank.

Turning the sender a few degrees counter-clockwise releases it.
Figure 8

Turning the sender a few degrees counter-clockwise releases it.

New fuel level senders often come with an O-ring.
Figure 9

New fuel level senders often come with an O-ring. The O-rings are available individually from Pelican Parts. Always replace the O-ring even if you replace the original sender.

Applying a light coating of oil to the O-ring eases installation.
Figure 10

Applying a light coating of oil to the O-ring eases installation.

With the O-ring lubed, the new sender could be twisted into its locked position by hand.
Figure 11

With the O-ring lubed, the new sender could be twisted into its locked position by hand. The rest of the job involved reversing the disassembly.

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