Electrical sensor on suspension travel??

[Midnightsun]

Was in the shop today putting on new Bridgestone Serenety tires and finally got a chance to take a good look at the under side of my car. I found a small switch which looks very much like a limit switch on the fron suspension. The suspension would activate the switch as it travels. Anybody have any idea what this is for? All fours have this by the way.

 

[mikec]

I browsed the factory service manual suspension section and there was no mention of limit/detect switches. So I'm curious too. I'll have to eyeball my car one of these days to see exactly what/where you're referring to.

The tire pressure system does have "activator" modules at each wheel to send RF energy to the in-wheel sensors - to power them. The manuals show a small box with ribs and corner attach feet... and one central electrical connection. Any chance that's what you noticed?

mike c.

 

[Mark_888]

Maybe has something to do with the Korean version, which has an air suspension system.

 

[Midnightsun]

Maybe has something to do with the Korean version, which has an air suspension system.

The same thought came to my mind but would make no sense cost wise to leave all this in place. All connectors, wiring, switches, articulating arms are all in place? Will snap a couple of pics if I can get in there with my camera.

 

[Midnightsun]

Pics are not as good as I wanted since I put the camera behind the wheel well and shot. Anyway, you can see both front and rear switch setups here. Notice the vertical arm connected to the suspension, the top portion of this is connected to the switch.

Rear Wheel

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Front Wheel

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[Midnightsun]

I browsed the factory service manual suspension section and there was no mention of limit/detect switches. So I'm curious too. I'll have to eyeball my car one of these days to see exactly what/where you're referring to.

The tire pressure system does have "activator" modules at each wheel to send RF energy to the in-wheel sensors - to power them. The manuals show a small box with ribs and corner attach feet... and one central electrical connection. Any chance that's what you noticed?

mike c.

If you are referring to the tpms, no. We do not get this on the Canadian models and thank god for that. I had this on my Murano and was such a pain in the butt. Problem up here in winter is the monitoring system is frequently telling you you have a flat tire!! When it gets to 20 below and less here in winter the tire pressure is less as we all know. Air pressure increases when heated but also decreases when cooled. If I did not keep my pressure up to 38 or 39 lbs it would give me flat warnings on very cold mornings. Setting the pressure to such a high figure is incorrect as during the day when temps warm up I would now be riding with about 6 lbs too much. Until the day comes when they interconnect exterior temp to correlate info with the tpms to eliminate these false warnings I really do not want this in any vehicle. I am sure it works very well for warmer winter climates.

 

[tjc78]

My best guess for these is something to do with the stability control system.

 

[mikec]

Great pics! From those I was able to match them up with sketches in chapter 13 "Body Electrical system" and verify they're for the auto-leveling headlight system. The system compares readings from front sensors to rear sensors to know what angle to aim the headlights at. They're called "VLS" or Vehicle Load Sensors.

Do the sensors exist on both the driver and passenger sides of the car or not? The manuals imply that there is one sensor on each end of the car, not on each wheel/suspension. The system apparently samples one side of the car only.

mike c.

 

[Midnightsun]

I assumed they were on all fours but double checked and sure enough they are only located front and back on the drivers side. Thanks for the answer. Sounds complicated for a levelling system considering an Iphone can do all that plus a heck of a lot more with 1 sensor and about 40 ft less wiring. Thanks again.

 

[mikec]

By comparing the suspension travel at each end of the car the computer/system can figure the angle regardless of the angle of the road. A single angle/tilt sensor (iPhone) can tell the TOTAL angle = Road + car. Don't want to use that to aim headlights! Sitting in a typical sloped driveway the headlights would either aim down (nose of car uphill in the driveway) or would aim at the stars if you backed into the driveway as I do.

Many older pick-up trucks and vans have a similar "weight sensing" linkage on the rear axle to control the brake proportioning valve: with no load in the truck, the rear brakes can't do much so most brake fluid pressure is directed to the front brakes. When fully loaded (and thus squatting on the suspension) the valve allows a lot more brake pressure to the rear brakes. Folks that add those "lift kits" or otherwise alter their suspensions often screw up the braking system because they don't correct this mechanical sensor's input. On modern vehicles such a sensor is no longer as necessary: with 3 or 4 channel anti-lock brakes the ABS system automatically distributes the brake fluid pressure to the various axles/wheels.

mike c.

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