Late puma with traction control - brake warning light comes on when descending

[Tote]

Today we were out playing a bit doing a recce for a club trip next month. My November 2015 build 130 was displaying some strange behaviour when descending steep hills.
The scenario- descending a reasonably steep hill, centre diff locked low range 1st gear - the brake warning light would flash when descending the hill and the vehicle appeared to behave as if it was being slowed although there was not the usual symphony associated with HDC in other vehicles
Similar descent in second gear low range the light could not be persuaded to light up under any circumstances so it is not likely to be a short or brake fluid level etc.


Has anyone else with a puma equipped with traction control experienced this feature?


Regards,

Tote

[Tote]

Found some more info:
While descending the brake light in the dash comes on intermittently, I read somewhere that the Puma actually has a type of a HDC but unlike in other vehicles that use ABS to slow the vehicle down, the ECU controls the engine speed, I have also read that if the ECU doesn’t do this the engine braking is so good due to the very low 1st gear that the vehicle would actually slide down the slope as if the brakes are being used incorrectly?

From here:https://www.google.com.au/url'sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja&uact=8&ved=0ahUKEwjpy6_3-OLVAhXEJpQKHcG3ATkQFghcMAk&url=http%3A%2F%2Fwww.4x4community.co.za%2Fforum%2F showthread.php%2F20377-Test-Drove-The-New-Defender%2Fpage2&usg=AFQjCNHj48iOwWuvp89eTnrNrSdRO8nNDw

Regards,
Tote

[jimr1]

This is a good question , I also have a 2015 Defender . We that's my son and I noticed coming down steep hills in the Vic high country that was also in low range 1st and 2nd the engine behaved different , at times it even reved higher . My son is a Land Rover trained mechanic but no longer works on them . He was having a drive and noticed it first , he said look at this I don't like it . It was all good we were safe enough . I questioned Land Rover dealership about it , the guy there said they're suposed to do that ? I don't know have an open mind on this one ? Jim

[tact]

My 2013 Defender doesn't have ABS/TC so cannot comment on that.

All the later model (TDCi) defenders have a feature called "idle jack". This feature is present regardless whether ABS/TC is fitted.

As has been mentioned LR engineers determined that in low first/reverse with engine at idle the wheels of a TDCi turn slower than is deemed optimal for safe descent on a steep hill. (A function of the low gearing, nothing to do with any electronic HDC action).

To correct this the TDCi ECU jacks up the engine idle speed by a few hundred RPM (from around 850 to ~1100 rpm) so long as ALL the following conditions are true:
- low range selected
- first OR reverse gear is selected
- clutch pedal position is close to fully up

[tact]

The TDCi "idle jack" feature can catch you out if unaware how it works.

Imagine you want very careful controlled centimetre precise movement (forward or backward), there may be a small ledge or tree root at your wheel to overcome, and you are in low first/rev. As you carefully allow the clutch pedal off the floor and your vehicle is predictably taking up strain and maybe moving very slowly... comes a time the clutch pedal reaches the level where the ECU decides to ramp up the engine speed a few hundred RPM. It can cause you to lurch forward a bit more than you may have been expecting.

So so do remember it's there.

[Tote]

The experience that I had was at rpms that were higher than those that Idle jack would apply to. Without being able to gauge exactly I would say that I was at 1800-2000 rpm down a steep slope in low first on a closed throttle. My suspicion is that when I lost traction on a wheel and that wheel stopped rotating the engine management kicked in and fed fuel to the engine to prevent a stall. I'll do some further testing next time I'm off road. I like discovering (almost) undocumented features! For what its worth most of the documentation I can find refers to all puma vehicles so it may not just be the late ones.

Regards,
Tote

[The Cone of Silence]

My 2013 Defender doesn't have ABS/TC so cannot comment on that.


I thought all 2007+ vehicles had TC and ABS. Is this not the case with some of them? Which ones?

[tact]

I thought all 2007+ vehicles had TC and ABS. Is this not the case with some of them? Which ones?


(...mine was assembled in Malaysia. Doesn't have the same options available as Oz.)

[Tote]

TC and ABS was a $2500 option on my 130

Regards,
Tote

[vnx205]

I know that you have no reason to believe that the light was activated by a low fluid level, but I was astonished at how little the level needed to be below full to cause the light to come on in my 300Tdi.

Seeing the light flash a couple of times on quite steep descents, I stopped and checked the fluid level. It could not have been more than a couple of millimetres below the full mark, so I dismissed that as the cause of the problem. Later I added a tiny bit of fluid to get right up to the full mark and I haven't seen the light since.

The drop in the level could only have been caused by the fact that the pads were partially worn, so the pistons had to move further.

In my case it seemed to be a combination of a tiny drop in the level, a quite steep descent and a slight lurch to trigger the warning.

[tact]

I know that you have no reason to believe that the light was activated by a low fluid level, but I was astonished at how little the level needed to be below full to cause the light to come on in my 300Tdi.

Seeing the light flash a couple of times on quite steep descents, I stopped and checked the fluid level. It could not have been more than a couple of millimetres below the full mark, so I dismissed that as the cause of the problem. Later I added a tiny bit of fluid to get right up to the full mark and I haven't seen the light since.

[...]

This is the case with the TDCi models too. Just the slightest drop in fluid level (as pads wear etc) can cause the brake light to come on - on downhills, and even when the vehicle is decelerating on engine compression.

[tact]

The experience that I had was at rpms that were higher than those that Idle jack would apply to. Without being able to gauge exactly I would say that I was at 1800-2000 rpm down a steep slope in low first on a closed throttle. My suspicion is that when I lost traction on a wheel and that wheel stopped rotating the engine management kicked in and fed fuel to the engine to prevent a stall. I'll do some further testing next time I'm off road. I like discovering (almost) undocumented features! For what its worth most of the documentation I can find refers to all puma vehicles so it may not just be the late ones.

Regards,
Tote

Am completely ignorant as to how an ABS/TC equipped Defender will behave on a steep downhill where a wheel loses traction. Were you on the brakes in the scenario you described?

Not sure if this thread on another site addresses your experience? Traction Control completely useless downhill! (http://www.4x4community.co.za/forum/showthread.php/64670-Traction-Control-completely-useless-downhill)!

I typically like to take a "feet off" approach to steep descents. I know that my own vehicle (no ABS/TC) could run away on a steep descent, if one wheel lost its grip on the earth briefly and the centre diff were not locked. So of course locked centre diff is essential. With the centre diff locked then it would require two wheels (one on each axle) to lose contact with the ground before it runs away. And that has happened, being crossaxled on a steep downhill. Just need to cover the brake lightly to keep some weight on the ATBs (front and rear) and not touch the clutch.

[Tote]

Pretty sure it's not the fluid level as it does not happen in second gear on similar descents at the same steepness. The light also did not appear to be randomly flashing or altering with the angle of the vehicle as you would expect if it was a low fluid level warning but appeared to be reflecting an action that the electronics were taking in response to the terrain. I can see I'll have to video the behaviour next time so we can analyse further. I'm surprised that someone on here hasn't noticed it happening though.
Descents were feet off both throttle and brakes with the descents being steep enough to require a little feathering of the brake pedal as revs rose in 2nd gear, not necessary in first due to increased engine braking.
Tact, you are right about the diff lock limiting wheel spin as one wheel comes off the ground so that can't be what its doing. Maybe it's just adding fuel to stop the engine stalling? I haven't noticed it when I have my foot on the throttle so some more experimentation is required.

Regards,
Tote

[DiscoMick]

Am completely ignorant as to how an ABS/TC equipped Defender will behave on a steep downhill where a wheel loses traction. Were you on the brakes in the scenario you described?

Not sure if this thread on another site addresses your experience? Traction Control completely useless downhill! (http://www.4x4community.co.za/forum/showthread.php/64670-Traction-Control-completely-useless-downhill)!

I typically like to take a "feet off" approach to steep descents. I know that my own vehicle (no ABS/TC) could run away on a steep descent, if one wheel lost its grip on the earth briefly and the centre diff were not locked. So of course locked centre diff is essential. With the centre diff locked then it would require two wheels (one on each axle) to lose contact with the ground before it runs away. And that has happened, being crossaxled on a steep downhill. Just need to cover the brake lightly to keep some weight on the ATBs (front and rear) and not touch the clutch.
Low first is so low in my six speed Puma that I have had to accelerate downhill.

[tact]

Low first is so low in my six speed Puma that I have had to accelerate downhill.

Yeah that's true at times - if the hill is such that idling down is sleep inducing, I give it a bit of throttle (or use a taller gear).

Have also been in situations where a bit of throttle is needed on long slippery hills to keep the sharp end pointed downhill