Discovery 4 not holding speed in cruise control

[eddielines]

Hi All

Just wanted to check if any one has had similar issue.

I've done a search and can find plenty on cruise control just not working, and causes including break light switch, clock spring, etc however my scenario is a bit different.

On the flat I can set and it will work, but on any sort of incline speed will fall, and it will not drop a gear or accelerate to keep speed. Where I can find cases of this its on older vehicles where the throttle was controlled by vacuum, but on these cars its all electronic. I don't use cruise that often but know it was working better than this before including at least attempting to keep speed on hills (success subject to steepness and load).

I have changed the clock spring anyway as there was some unusual behaviour with buttons on wheel when i pressed quickly, horn was intermittently not working (quit a while back) and I could hear a very slight dry whine when turning steering wheel at times.

Has any one had similar or any ideas on where I should start ?

[Graeme]

Others have had what seems to be the same issue, resolved by recalibrating a sensor that's located under the centre console. I can't recall its name but it could be a longitudinal accelerometer that detects when the vehicle is travelling uphill, used by cruise control.

[DiscoJeffster]

Others have had what seems to be the same issue, resolved by recalibrating a sensor that's located under the centre console. I can't recall its name but it could be a longitudinal accelerometer that detects when the vehicle is travelling uphill, used by cruise control.

Yes! There is a thread on this. OP have a search and you’ll find it

[eddielines]

Thanks Guys

Found it D4 cruise control runs away

And yes, took 2 mins and sorted the issue. Now holding speed to within 1-2 KMs.

Now on to next job.

[LuckyLes]

Does anyone have the problem, when using cruise control, that on a downhill the car will run on, not accellorating just coasting and gain speed with no retardation? I frequently travel a longish decline of about a kilo or thereabouts cruise set at 100 but by the foot of the hill , i wil be at 125 and still in 8th gear. Should it drop back a couple of gears to slow the car? I have had on occasions accelaraion going up hill, so that I have to disengage CC
Cheers
LuckyLes

[Graeme]

Early 3.0 D4s would run away like this because the throttle wasn't closed (instant fuel consumption showed fuel being consumed) then LR released at least 2 updates, the 1st reduced the fuel consumption then eventually shut-off fuel completely on significant over-run which made a big difference to the extent of the over-run.

[LuckyLes]

Are the updates available via Gap IID or do I need to take it to a dealer?

[loanrangie]

Are the updates available via Gap IID or do I need to take it to a dealer?

Likely to be available via their fast lane service and would be cheaper than LR I would expect.

[eddielines]

Those updates are on the Engine ECU ?

Mine is 3010 and I do get the over run.

[Graeme]

Yes, the PCM. However I would expect that those early updates would have been applied at a service many years ago.

Display the current fuel consumption whilst over-running. If it's zero then those updates have been done but not done if anything above zero, even 0.1 L/100.