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Thread: Rough road active, knock detection inactive

  1. 15th January 2016, 05:28 PM #1
    D2lee
    D2lee is offline Master
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    Rough road active, knock detection inactive

    hi all,

    my D2a 4.0 V8 seems to run fine and I'm running it on 95RON. No fault codes.
    However, when I check with NANOCOM, the rough road signal is cycling between 0 and 12v regularly every second and rough road is active, hence knock detection is inactive. This occurs both when the engine is running and engine off (ign2 position).

    It's similar to the issue in the link below, which nobody had heard of and didn't get resolved as far as I can see.

    2000 Disco Rough road mode help - Land Rover Forums : Land Rover and Range Rover Forum

    According to RAVE, this signal is PWM, so that might explain why nanocom see's alternating 0-12v. 25% duty cycle indicates a smooth road, so I need to get my scope on the signal to see what's coming out of the slabs ECU.

    Also from RAVE;

    Off-road detection is achieved by the SLABS ECU by monitoring the signals from the upper and lower accelerometers for varying degrees of body movement. Off-road driving generates differing signals to the accelerometers which in turn produce differing outputs due to their vertical separation and the location of the roll centre of the vehicle. The two signals are passed through a filter to remove any offset caused by the vehicle leaning or the terrain. The ECU then uses this signal to calculate the percentage of road roughness.Below 25 mph (40 km/h) the percentage of road roughness calculated is used by the ECU to limit the operation of the ACE system. The system is completely inoperative at speeds below 2 mph (3 km/h).

    So I wonder why it's still active when the vehicle is stationary

    Confusingly, the rest of RAVE only seems to refer to accelerometers as part of the ACE system (which I don't have and it turned off in NANOCOM) and they seem to only connect to the ACE system, so I can't see how they relate to SLABS.

    Has anyone heard of this issue and how to fix it?
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  2. 16th January 2016, 10:34 PM #2
    schuy1 Guest
    If the car is running fine what is there to fix? Accelerometers are used in both the ACE system and for SRS airbag deployment . It says in your quote why SLABS uses the input. I can only assume maybe the accelerometers you see being used are the airbag 1? Maybe its linked some how the the "rough terrain" as a guard to them deploying prematurely? Some 1 may know.
    Cheers Scott
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  3. 18th January 2016, 09:00 AM #3
    D2lee
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    my main concern was with knock detection being inactive, which could lead to preignition or incorrect advance.

    However, having monitored NANOCOM more closely when driving, I actually saw knock detection becoming active under load, so that side of things seems to be working correctly.

    One interesting thing though; the rough road signal seems to be inverted. This could simply be NANOCOM reading a 0 as active instead of 1 or vice versa.

    Basically, driving a smooth road, rough road is active, but as soon as I go over a bump, it says rough road inactive! But as knock detect seems ok, I think it's just a NANOCOM config issue.
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  4. 19th January 2016, 05:28 PM #4
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    sierrafery
    sierrafery is offline YarnMaster Silver Subscriber
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    Hi, IMO as long as you dont get one of the rough road signal related fault codes(P1590,1591,1592) there's nothing wrong with the rough road input to the ECM

    the vehicle being non ACE from factory maybe the management is set by default to ignore this signal cos the only way the SLABS can get accelerometer inputs is through the ACE ECU as the accelerometers are connected only to this one, i can't see how the SLABS would generate a valid rough road signal without communication with the ACE ECU...

    i presume that the default for this case is a continuous rough road signal as you get with nanocom to override missfire detection... or there's a glitch in the reading

    IMO that's not fixable cos it's not ''considered" a problem by the management being fault code free.

    Unfortunately i know nothing about knock control
    Discovery Td5 (2000), manual, tuned
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