Cruise - Speed Control Input Voltage

[Skmitchell91]

Hey guys,
Been trying to chase down a cruise control issue for weeks now. Clock spring seems to be working, steering wheel look seems good too.
I've plugged in the IID and noticed I'm getting 0v on the Speed Control Input Voltage. Any idea what sends that voltage signal? Doing my head in

[DiscoJeffster]

Maybe explain what the problem is you’re trying to solve. That will be more helpful to resolving your issue [emoji1360]

[Skmitchell91]

Apologies.
The cruise control doesn't activate anymore. No fault codes.
2010 Disco 4, 2.7 TDV6

[Graeme]

I would replace the brake light switch unless already recently replaced.

[Skmitchell91]

I forgot how fun Land Rover electronics are

Had the cruise able to activate for about 5 seconds before cancelling itself on a drive today, and not reactivate. I took my foot off the accelerator once the cruise activated, wondering if maybe the sensor is having an issue? i don't have any fault codes on my GAP to do with cruise related items

[Graeme]

A faulty brake switch that indicates that the pedal has been pressed will cancel CC with the only indication the momentary message that CC has been cancelled. The brake switch is quite inexpensive and LR can sometimes be the cheapest source but as the switch is a Ford switch it can be purchased from many sources.
The switch has 2 sets of contacts so even though the brake lights aren't on, CC can be cancelled or inhibitted.
I always carried a spare when I had a D4 because they commonly fail and can cause other systems to not operate fully because the brakes are applied.

[Tombie]

I forgot how fun Land Rover electronics are

Had the cruise able to activate for about 5 seconds before cancelling itself on a drive today, and not reactivate. I took my foot off the accelerator once the cruise activated, wondering if maybe the sensor is having an issue? i don't have any fault codes on my GAP to do with cruise related items

Bit of a non-sense flash back there [bigwhistle] No LR electrical in the vehicle what-so-ever....

Welcome to Canbus - something universal....

[BradC]

Bit of a non-sense flash back there [bigwhistle] No LR electrical in the vehicle what-so-ever....

Welcome to Canbus - something universal....

That's not quite correct. "CANBus" is simply a protocol that sits on a bus that's mostly electrically compatible with RS485 (differential pair). So the electrical characteristics are defined, along with the low level protocol. The electrics in the vehicle that aren't made by Ford are mostly still assembled and completely wired by Landrover, as is the configuration. So yeah, it's still "LR" electrics. It's just that most of the modules (the ones that aren't LIN Bus) speak CAN.

[Old Farang]

The ins and outs of CanBus:

"Achtung!
Alle touristen und non-technischen lookenpeepers! Das machine is nicht fur fingerpoken und mittengrabben. Is easy schnappen der springenwerk, blowenfusen und poppencorken mit spitzen sparken. Das machine is diggen by experten only. Is nicht fur gerwerken by das dummkopfen. Das rubbernecken sightseeren keepen das cottenpicken hands in das pockets. Relaxen und watchen das blinkenlights."

Actually, later Land Rovers are using a more modern protocol:

CAN bus is an interesting subject but quite old technology now that JLR are gradually phasing out with the introduction of Flexray and other networks

[Skmitchell91]

I'll throw a new brake switch in and see how it goes. Interesting that it isn't throwing a code and the lights still work fine, but i digress.
I'm not seeing 5V on the Speed Control Input on my GAP which i think i should be seeing? Following the wire diagrams is a PITA to see where this is coming from, but i know i have voltage coming in and out of the clockspring

[Graeme]

I suspect that the Gap tool shows the brake light switch status - it's not something that I recall having checked.

[Old Farang]

I suspect that the Gap tool shows the brake light switch status - it's not something that I recall having checked.
I doubt that it will, even if it is faulty. Should be NC if no brake action, will become open when the brake pedal is moved. If it has failed open, then the system will see it as the brake being activated and stop any further bootup.

[BradC]

Should be NC if no brake action, will become open when the brake pedal is moved.

It is both NC and NO. 2 separate sets of contacts. The car gets awfully confused if they don't actuate at very close to the same time.

[Old Farang]

It is both NC and NO. 2 separate sets of contacts. The car gets awfully confused if they don't actuate at very close to the same time.
Years since I dug into this stuff, but my understanding is that 1 contact is for the brake light, and the other for the cruise control. There is a string of sensors in that loop for the cruise control, but the brake pedal contact "should" not get confused, even allowing for CanBus.

Need to remember that CanBus was used for the very early cruise controls that had a vacuum actuator and a bit of steel wire connected to a thing called a carburetor!

[BradC]

Years since I dug into this stuff, but my understanding is that 1 contact is for the brake light, and the other for the cruise control. There is a string of sensors in that loop for the cruise control, but the brake pedal contact "should" not get confused, even allowing for CanBus.

Need to remember that CanBus was used for the very early cruise controls that had a vacuum actuator and a bit of steel wire connected to a thing called a carburetor!

One contact is for the brake light, but that's also monitored by the CJB, ECM and ABS modules. That connection allows the ABS module to turn on the brake lights when in HDC mode.
The second contact is connected directly to the ABS module as a sensor input. If the ABS module sees an implausible signal because of a dodgy contact then it causes cascading faults across the network.

[PerthDisco]

Driving recently on a long fast graded track at about 80 with CC on when you come into a patch of more serious corrugations the CC would switch off which I imagine was wheel speed sensor related some mismatch outside parameters.

[Graeme]

That should have produced an ABS fault but not if the cause was the brake pedal bouncing a little.

[PerthDisco]

That should have produced an ABS fault but not if the cause was the brake pedal bouncing a little.

Very possible that scenario

[BradC]

From hazy memory the CC drops out if any form of DSC event happens, and even turning the DSC off doesn't completely disable all elements of it, it just stops you getting bogged on the beach.

Just checked. Service manual says "Even if DSC is deselected, driving manoeuvres with extreme yaw or lateral acceleration may trigger DSC activity to assist vehicle stability". I'm pretty sure I triggered it skating across a corrugated gravel road on an off camber corner.

[Skmitchell91]

No go on the new brake switch. Thinking that the reference from the switch isn't working. Anyone know where the reference voltage comes from/to with regards to the ECU?

[BradC]

Check the wiring diagram : Later D3 wiring diagrams (https://www.aulro.com/afvb/l319-discovery-3-and-4-a/285102-later-d3-wiring-diagrams-post3122040.html#post3122040)

On the D3 both sides of the brake switch come from separate fuses. I'd assume the 4 is similar but the wiring diagram is the way to enlightenment.

Edit : And I'd be wrong. S215 on the diagram. Brake light side (NO) goes from Fuse 14P to the BCM (brake light power). The NC side goes from the ECM to ground.

[Graeme]

Can the IIDtool monitor the status of the CC enable and CC cancel buttons?

[BradC]

Can the IIDtool monitor the status of the CC enable and CC cancel buttons?

It must be able to. That's its primary user interface.

Edit : On the D3 under TDV6 ECM it's the "Speed Control Input Voltage". That gives the voltage on the resistor ladder for the 6 CC buttons. Mine idles at about 4.1V.

[Graeme]

My expectations, but my L322 might be different so a check might not be valid for a D4.

[BradC]

Shoulda checked the wiring diagram. The D4 audio side controls are a resistor ladder same as the 3, but it looks like the cruise switches and flappy paddles connect to a LIN module which goes to the BCM. On that note, I'll back away slowly.

[Skmitchell91]

It must be able to. That's its primary user interface.

Edit : On the D3 under TDV6 ECM it's the "Speed Control Input Voltage". That gives the voltage on the resistor ladder for the 6 CC buttons. Mine idles at about 4.1V.

I'm not getting any voltage reading which is where i guess my issue lays. But i'm getting voltage into the clock spring, and i've put a new clockspring in...interesting

[BradC]

I'm not getting any voltage reading which is where i guess my issue lays. But i'm getting voltage into the clock spring, and i've put a new clockspring in...interesting

It looks like the D4 uses a little processor in the steering wheel and a one wire LIN bus to the BCM, so you won't see a voltage in the GAP. It'll be an asynchronous serial connection.

Now, easy test is plug the GAP in and try to use its dashboard interface. It's navigated with the cruise control buttons. If that works the problem is elsewhere.

[Graeme]

The switches have been known to fail.

[Skmitchell91]

The switches have been known to fail.

Guess a new switch pack is on the card then [bawl]

Put on the GAP and it's not showing any of the Set Speed buttons as being pushed, strange that all would fail at once. I'll try to chase down a loom too i guess, do all at once

[Graeme]

I have a recollection of the existance a loom connecting both switches and therefore the right switch bank may have an impact, but I may be confusing the D4 with my L322 to which I retro-fitted ACC which required a different left switch bank.

[Skmitchell91]

So driving home today, held the "set" button in and just had a bit of a tap around the steering area, was able to get a "cruise not available" error pop up, and continue popping up whenever i pressed a cruise button. Showing fault code P0570 which seems to relate to the set button, so the signal is obviously getting through. I'll order and replace the switch pack and loom just to be on the safe side

[Skmitchell91]

So update, new clock spring and steering wheel control, still no cruise. Have a new clock spring to SWC loom coming, see how that goes.
Anyone got any other ideas?

[TonyC]

You haven't responded to posts 25 and 27 from BradC.

Have you looked at your LIN module?

I have no idea what it is, but I'm willing to bet my 95 300Tdi Defender doesn't have one.

Tony

[BradC]

So update, new clock spring and steering wheel control, still no cruise. Have a new clock spring to SWC loom coming, see how that goes.
Anyone got any other ideas?

Does the D4 cruise rely on an accelerometer that might need calibrating? "Longitudinal Accelerometer Sensor calibration."?

[Graeme]

The longitudinal accelerometer is fitted but if out of calibration enough to prevent CC from being enabled then I would expect a DTC, but worth using the Gap tool to reset it while on a very level surface.

[BradC]

I don't have a D4, so I'm clutching at straws.

[Skmitchell91]

So! Thanks for everyones help on this, it's been a whole ordeal.

Turns out it had nothing to do with the cruise at all, and the park brake was SLIGHTLY dragging. Readjustment of the park brake and everything is working as it should.

Go team

[BradC]

Quick question if I may. How much did you spend on "parts canon" parts before you discovered it was a mal-adjusted park brake?

I know these are complex beats, and I'm not doubting your diagnosis, but I'm really, really struggling to understand how a dragging park brake could cause the cruise control to misbehave. Like so badly you can't operate the GAP tool on the dashboard with the cruise control buttons.

I keep adding 1 and 1 and coming up with 3.

[Graeme]

I wonder if the EPB switch with its multiple contacts was the real culprit although I would have expected a DTC if it was both on and off.

How was the slightly dragging park brake discovered?