Parking sensor question

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Martyn_n

Active Member
Joined
Nov 27, 2010
Messages
928
Location
Leicester
Car
W124 E320, W163 ML270 & W166 ML350
I have just bought a W166 ML and I have found that the rear parking sensors are not working correctly. When you engage reverse gear the four red lights light up and the beeper sounds for about a second. The manual states that this is not a failure of the parking sensors as that is followed by the parking sensors turning off and the red light on the parking sensor switch lighting. According to the manual it is dirty sensors (they are not) or interference and you should drive somewhere else (Somewhere else isn't necessarily where I want to park and it doesn't change things anyway).
Has anyone else experienced this, and if so what fixed it? The car is Mercedes "Approved used" so it has a warranty but do you think it will cover this as the manual says it isn't a fault unless the parking sensors turn themselves off.
Any insights would be appreciated.
 
The sensors make a slight noise when they are switched on. Switch the engine off and turn the ignition on and select reverse if you put your ear to the sensors they should all make a slight noise.
 
The sensors make a slight noise when they are switched on. Switch the engine off and turn the ignition on and select reverse if you put your ear to the sensors they should all make a slight noise.
I should give that a go but I have assumed that if it was a faulty sensor the system would shut down as it does on my other car. Frustratingly the parktronic system isn't visible to my diagnostic tool on the 166 for some reason which doesn't help.
 
You'll find they deteriorate at the rubber seal on the side of the sensor. This let's in moisture and shorts them out. When they dry out they begin working again until it rains.
 
You'll find they deteriorate at the rubber seal on the side of the sensor. This let's in moisture and shorts them out. When they dry out they begin working again until it rains.
But would that not result in the system shutting down as faulty rather than indicating a dirty sensor. From experience in the 163 any faulty sensor soon tripped the system out.
Anyone know if the 166 bumper is as easy to remove as the 163? if it is I will drop it off and have a good look at the sensors for any sign of deterioration.
 
But would that not result in the system shutting down as faulty rather than indicating a dirty sensor. From experience in the 163 any faulty sensor soon tripped the system out.
Anyone know if the 166 bumper is as easy to remove as the 163? if it is I will drop it off and have a good look at the sensors for any sign of deterioration.

Sorry , I can only offer possibles not definites.
 
the area i marked in red is rubber sealant , the problems i had with parktronic shutting down was rain/moisture getting in . using wd40 for weeks beforehand seemed to make the rubber soft and gooey .so i did infact make things worse trying to make things better.
 

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the area i marked in red is rubber sealant , the problems i had with parktronic shutting down was rain/moisture getting in . using wd40 for weeks beforehand seemed to make the rubber soft and gooey .so i did infact make things worse trying to make things better.
Thanks for the info, I'll have a look and see if they are deteriorating in that area.
 
An update, I have managed to narrow it down to sensor number ten being faulty (I told my diagnostic tool it was a 212 not a 166) Any idea which sensor is number ten, I'm assuming it is one of the rear outer ones.
 
Ign on in reverse and put your lugs upto each one. The sensor not blipping is at fault.
 
you don't need to remove the bumper to change a sensor. I did mine lying down under the bumper. The old one just unclips and the new one is pushed in. Merc sold me a sensor with a pot of silver paint to match the car
 
you don't need to remove the bumper to change a sensor. I did mine lying down under the bumper. The old one just unclips and the new one is pushed in. Merc sold me a sensor with a pot of silver paint to match the car
Which model was that on Tom?
 
If you get 4 red lights followed by a long beep and then the parktronic button lights up that indicates a fault in the system. Best way I have found d to test the sensors is to put into reverse with the ignition on and park brake on and gently hover your finger over each sensor you should feel a slight pulse effect that means the sensors is working the one that doesn't pulse is defective. Have you put on a diag machine to see if any faults ?
 

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