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

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Originally Posted by 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.

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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.

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Originally Posted by 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

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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!!

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.

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

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Originally Posted by tact

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!!

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.

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

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Originally Posted by DiscoMick

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

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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