2010 Mercedes-Benz S400 Engine Oil Level Sensor Replacement Cost

The engine in a car, truck, or SUV contains many metal components that produce friction when they are moving. Oil is used as a lubricant to reduce this friction and to mitigate the heat that is generated in the engine. Over time, the oil will break down, primarily because of the heat. Therefore, oil replacement is an important part of routine vehicle maintenance. When the oil begins to degrade, it loses some of its lubricating and cooling properties. If left for too long, the degraded oil forms a sludge that builds up on engine components and in the bottom of the oil pan. The oil level will also drop. When the oil level decreases, the thermal breakdown (and other forms of oil degradation) is accelerated. This accelerated breakdown of the oil can happen when the engine has an oil leak as well. To alert the driver to a low oil condition in the engine - whether from breakdown or from a leak - an engine oil level sensor located in the oil pan triggers a warning lamp on the dashboard.

An engine oil level sensor uses a float switch inside the oil pan that is normally off when the engine oil level is within an acceptable range. When the level drops, the float drops and the switch turns on, sending a signal to the Powertrain Control Module (PCM) which, in turn, lights up the oil level warning lamp on the dashboard. The PCM monitors the oil level and engine temperature when the engine is in operation.

A bad oil level sensor may cause a false reading of the engine oil level. The oil level warning light may illuminate even when the oil level (checked manually) is within an acceptable range. The warning light may also come on and off intermittently if the sensor is faulty. An error code may be sent to the PCM and a check engine light may come on the dashboard as well if the sensor is bad.

A vehicle with a bad oil level sensor can be driven if it is not causing additional problems because of false signals sent to the PCM. The sensor is not critical to basic engine function, however it is an important safeguard and should be changed as soon as possible.

The engine oil level sensor does not have a scheduled maintenance or replacement schedule and should last the lifetime of the vehicle. However, the sensor is exposed to harsh conditions and may be prone to wear and premature failure.

If the engine oil level warning light is on, or if it intermittently lights up on the dashboard, but the oil level in the engine is normal, a technician will recognize that the oil level sensor is bad. In some cases, a diagnostic scan with a special scan tool connected to the vehicle's computer system may read a trouble code revealing a bad sensor.

To replace a bad engine oil level sensor, a technician will lift and support the vehicle, drain the oil, remove the bad sensor, and install a new one. The oil (and filter) are replaced and the vehicle is lowered to the ground. The technician will start the vehicle to make sure that the sensor is operating properly and that there are no engine oil leaks.

When the engine is first started, the oil level warning light, along with the other warning lights, will illuminate on the dashboard momentarily. This is a normal operation as the vehicle's computers go through a diagnostic check of the vehicle systems. If the oil level warning light remains lit, the oil level should be manually checked with the dipstick. If the oil level is within the acceptable range on the dipstick, but the warning light is on, there may be a problem with the sensor. If the oil level is low, oil should be added to the engine immediately. In either case, the vehicle should be inspected by a qualified technician at a trusted repair facility to determine what the cause of the problem might be, whether a faulty sensor or an oil consumption problem.

A low oil level is no small problem. If caught early, damage to the engine may be prevented. However, low oil is not merely a problem, it is a symptom. A low oil level can be caused by an oil leak in one or more of several places in the engine. Alternately, a low oil level can be caused by oil that has been neglected through infrequent oil changes, leading to engine oil sludge and clogged engine components. If the oil level warning light comes on, the oil level should be checked and topped off if it is found to be low. The cause of the low oil condition should be investigated as soon as possible. If the oil level is considerably low - below the "low" level on the dipstick - the vehicle should not be driven until oil has been added.

Because it is necessary to lift and support a vehicle in order to replace an engine oil level sensor, the repair should only be done by someone with an intermediate level of DIY experience. Otherwise, it is best left to a repair professional.