dguy

Rough Road Sensor

20 posts in this topic

Hello,

 

Does anyone happen to know the location of the Rough Road Sensor in a 451?  OBD claims that ours has an intermittent open circuit and I would like to check it out.

 

-d.

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could it be the Yaw/Lateral Movement/G-Force Sensor ?

What Does It Do?
Measures the lateral forces of the car.
What Happens If It Is Faulty?
ESP or Trust warning light will show, you may lose drive or safety systems can shut off.
Where Are They?
600cc - Underneath the undertray on the nearside.



700cc - Underneath the seat, underneath the carpet.

 

 

found online via evilution site https://www.evilution.co.uk/495

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There's no "rough road" sensor on the 451.  What OBD code did you use to get that? :)

 

If it turns out to be the yaw rate/lateral G sensor, it's underneath the driver's seat:

yaw%20ratw%20sensor_zpsvroak763.jpg

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8 hours ago, jwight said:

There's no "rough road" sensor on the 451.  What OBD code did you use to get that? :)

 

P0318, intermittent open circuit. From a scan with Delphi 2015.3 and a DS-100E.

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After some bathroom reading, it would seem that P0318 is set when data from any of a collection of sensors may be interpreted as a rough road contributing to the anomalous reading.  In other words, P0318 is somewhat of a red herring.

 

We also have an intermittent implausible signal from the left rear wheel speed sensor. It won't surprise me if resolving that will clear the "rough road" error as well.

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14 minutes ago, tolsen said:

Perhaps a cracked abs ring?

Damn...beat me to it again...lol....and an easy fix and inexpensive.  I also tell everybody.......check all your grounding locations that are any where near close to the problem you are suffering......open them all up and check each and every eye connector for any corrosion at all then when re-assembling, use a smeer of dilectric grease to help prevent it happening again at that pin.

 

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I'm definitely not discounting a cracked ABS ring, but from my experience they're an "on or off" issue.  Once they crack sufficiently to throw off a sensor reading, the error will persist until resolved.  This really is a sporadic wet weather-only error at the moment.

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30 minutes ago, dguy said:

I'm definitely not discounting a cracked ABS ring, but from my experience they're an "on or off" issue.  Once they crack sufficiently to throw off a sensor reading, the error will persist until resolved.  This really is a sporadic wet weather-only error at the moment.

As it's a wet road only issue the traction control will will trigger with anything over a 2-3% difference in wheel speeds IIRC.

I trigger mine all the time on wet roads and parking lots.

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3 hours ago, BWM said:

As it's a wet road only issue the traction control will will trigger with anything over a 2-3% difference in wheel speeds IIRC.

I trigger mine all the time on wet roads and parking lots.

I can only trigger mine in very wet or snowy conditions as in the dash light lights up but then goes out once it see's things are back to normal.....it basically slows car down until it see's things are safe again. Amazing how well this system works, but annoying to say the least when you want more tire spn.  So I have a switch now to over ride this system on dash!....lol

 

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Posted (edited) · Report post

Following up...

 

Visual inspection of the left rear reluctor ring showed nothing out of the ordinary, so I replaced the sensor.  No change.

Many kms and another visual inspection of the components later, and I opted to run the car out to Troy W.

 

His analysis:

  • The ABS/ESP warning lights came on during a road test, however a live data scan showed a good signal from all speed sensors.
  • No excessive play in the wheel bearing.
  • The rear tires are a hair undersize compared to OE, but not enough to trigger a speed differential code.
  • Wiring from the rear speed sensors up to the ABS module is perfect.

All signs are pointing to the ABS module not appreciating wet conditions. 

I know that Delphi and a DS-100 can perform an ABS module bleed.  Does anyone happen to know if it can also marry a new ABS module to the car, or is that a dealer visit?

Edited by dguy
DS-150 vs DS-100 correction

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Posted (edited) · Report post

FYI, if the ABS sensor gets a bad signal even briefly if the car is over 60 km/h, the ABS light will come on and ABS/ESP will shut off until the car is re-started. (This is what happened with my 450... I'm not sure if the 451 is any different.)

Edited by darren

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I had my car  light up yesterday on my trip down to London to visit Glenn.....We were scooting along around 100kmh in very wet conditions and it hydroplaned enough for me to easily feel the lift and all lights came on in a flash!   The speed was dropped by the car and it settled down and resumed normal operation.......I bet it would have been a completely different story if it wasn't working.....augh...!!!!!    I have tried my switch in the snow and it does allow some wheel spin but it's not like any other normal rear wheel car where it'll spin endlessly it seems.....no whether it max's out too quick or what I don't know but it still didn't spin around as fast as I was expecting...Hmmm....more play time is required...lol

 

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To clarify, since upon review it looks as though I didn't leave much detail of the symptoms... oops.

 

Dry weather - ABS/ESP warning lights will illuminate at random with no rhyme or reason, then reset after one or two ignition on/off cycles. 

 

Wet weather - the ESP system will frequently intervene as though the car is experiencing a skid or wheel spin when in fact everything is normal.  The ESP light does not always flash when this is happening, but throttle cut and/or brake application of individual wheels is painfully obvious.  Eventually it gives up and sets the warning lights.  As with above, the system will eventually reset after a few ignition on/off cycles.

 

A code for implausible signal from the left rear wheel speed sensor is set in all events, along with the "rough road sensor" red herring from my OP.

All inspect-able elements of the system are in good shape - reluctor rings, wheel bearings, wiring harnesses, you name it.  This pretty much leaves the ABS module as suspect.  I know Delphi has the bleed function, but if it can't marry a replacement ABS module to the car I'm stuck with a stealership visit.

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No, Glenn is a minimum 12 hour round trip from here.
My local go-to guy for Smart oddities is Troy Wilson (former MB mechanic at a local dealer).  He has a Mercedes scanner but believes that it may not be sufficiently up-to-date in order to code in a new ABS module.

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Troy has a good reputation in the Ottawa area, so he should be able to solve the issue sooner or later.

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Just a question for my own interest....will a STAR clone be able to the bleed procedure for the ABS module......as my good car was allowed to drain through...Hmmm...?...Damn!

 

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19 hours ago, Leadwing said:

Troy has a good reputation in the Ottawa area, so he should be able to solve the issue sooner or later.

 

Yes the car was in at Troy's on Wednesday, which is where the diagnosis of a likely failing ABS module came from.

 

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