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Oil Level Sensor Replacement
 
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Pelican Technical Article:

Oil Level Sensor Replacement

Tom Morr

Time:

1 hour1 hr

Tab:

$32 to $53

Talent:

**

Tools:

10mm socket, ratchet, wobble, extensions, 13mm socket or wrench, 1/4" drive ratchet with a wobble joint and extension(s)

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

Oil level sensor

Hot Tip:

Work on a cold engine

Performance Gain:

Restores proper operation of oil warning light
On paper, replacing the oil level sensor is a two-bolt job. In reality, some preliminary steps and a challenging-to-reach rear-mounting bolt make what seems like 15-minute jobs more like an hour-long project.

The oil-level sensor is basically a switch. Oil enters the sensor's chamber through its vent hole. The sensor uses a float and a magnet to determine oil level. When the oil level is within the minimum and maximum range noted on the dipstick, the contact is closed and the switch is grounded. If the oil level gets too low, the switch's contact opens. This signals the control module to illuminate the oil warning light on the instrument cluster.

If the oil warning light stays on during driving but the oil level is in the proper range on the dipstick (measured on level ground after the engine has cooled for at least 5 minutes), then the sensor might need to be replaced. An Engine Oil Level Service Required message on the instrument cluster is another tip-off that the sensor is bad. 

The oil will need to be drained below the sensor's bore in the oil pan. Many SLK owners might want to combine an oil change with sensor replacement, instead of trying to guess the correct level and attempting to plug the oil flow midstream.
The oil needs to be drained to below-sensor level.
Figure 1

The oil needs to be drained to below-sensor level. This is an opportune time for an oil change. A 13mm wrench or socket fits the oil pan plug.

The oil level sensor is located above the drain plug on the left side of the engine.
Figure 2

The oil level sensor is located above the drain plug on the left side of the engine. Two bolts (arrows) secure it to the oil pan. A wire plugs into a post on the sensor's center.

The outer bolt is easily accessible.
Figure 3

The outer bolt is easily accessible. A ÂÂÂ1/4-inch-drive ratchet and 10mm socket make quick work of it.

The plug pulls off the sensor's contact stud.
Figure 4

The plug pulls off the sensor's contact stud.

The inner bolt is trickier.
Figure 5

The inner bolt is trickier. A/C hoses and the body make access tight, limiting tool options.

The sensor will come out of the pan once its probe is rotated up to approximately the 11:00 position on the hole.
Figure 6

The sensor will come out of the pan once its probe is rotated up to approximately the 11:00 position on the hole. Then the unit can be shimmied out between the body and A/C hoses.

The oil level sensor and 40mm OD O-ring are normally replaced together.
Figure 7

The oil level sensor and 40mm OD O-ring are normally replaced together. However, the O-ring is available separately if the sensor is functional but oil is leaking around it.

After some trial and error, we were able to get the inner bolt off using a ÂÂÂ1/4-inch-drive ratchet with a wobble joint and about four inches of extensions.
Figure 8

After some trial and error, we were able to get the inner bolt off using a ÂÂÂ1/4-inch-drive ratchet with a wobble joint and about four inches of extensions.

The oil level sensor has a 60-second delay so that sloshing oil from spirited acceleration or cornering won't send a false warning.
Figure 9

The oil level sensor has a 60-second delay so that sloshing oil from spirited acceleration or cornering won't send a false warning. If the light remains on but the dipstick indicates proper oil level, the sensor needs replacing (assuming that the wiring and control module aren't faulty).

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Comments and Suggestions:
Rhuby Comments: oil sensor is always lighting in fact the oil level is in maximum
April 15, 2015
  Followup from the Pelican Staff: What vehicle? Could be a faulty sensor. - Nick at Pelican Parts  

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