Traction control/dpm switching off

[Gashead1105]

Odd one this. Occasionally over the past few months, my traction control switches off entirely, the TC light come on to show its all off and the DPM switch doesn't turn it back on. This seems to usually happen when I pull up to some traffic lights. It's not every drive, and the indicators, radio etc still work. Switching the car off and on seems to reset things. Has anyone else experienced similar? 

[Dunc1]

Had the same issue for a while and happened again this morning as I pulled in for fuel.  Every time I switch off and on it resets, I too would be interested to know why and how to resolve.

[TonyKL]

My guess is possibly a faulty/loose ABS/wheel sensor

[LotusPilot]

Dis anyone get to the bottom of this issue.  I’m seeing this problem on nearly every journey.

[Hangar 111]

There are a number of sensors which could cause this problem - ideally you need to get the Lotus diagnostics plugged in to work out which one.

Brake pedal switch might be worth a try if you want to start off with a guess.

Dave

[Mark030358]

As Dave says, brake pedal switch. My issue was the aftermarket lights, needed a resistor to "show" a load.

cheers

[LotusPilot]

Thanks guys - your input is much appreciated.  Rapidly falling out of love with my cherished Exige as this fault now occurs on every journey - no matter how short.  I was hoping the OP might have some insight into his resolution of the fault.

Spent today trying to systematically diagnose further - and I can now reliably recreate the problem at will...

Start engine, foot on brake pedal - and within 1 min the DPM drops-out with the TC warning light illuminated.  Same test, but without using the brake pedal, all is well - until the car is driven; the problem, when it occurs, always involves the brake pedal.  This pretty much directly correlates with the anecdotal comments by others, such as “pulling up to traffic lights” - which I see frequently and often when stopped.  Being stationary, this completely rules out any rotational sensors for ABS/wheel speed and steering angle.

The Lotus Service Manual implies that the brake switch is two-stage - one circuit feeds the brake lights and an input to the ABS Control Unit - the other circuit provides a single contact input into the ECU.  No fancy sensors in these circuits other than the brake switch - and the brake lights work just fine.

Edited October 23, 2018 by LotusPilot

[TBD]

You've diagnosed it quite well, change the brake switch.

[Hangar 111]

Agreed.  Assume "the Lotus position" - head down in the footwell

Dave

[LotusPilot]

Thanks again for your input - but I fear that interaction of the brake switch is more symptomatic than likely to be the root cause of the fault.  Testing of switch contacts suggests that the switch is good.

Edited October 24, 2018 by LotusPilot

[GFWilliams]

Have you checked your brake lights are working?

[LotusPilot]

Yes.  It is worth repeating that the circuit diagram shows the brake lights are fed from (on the same circuit as) the switched circuit providing an input to the ABS Controller.  The other switched circuit goes solely to the ECU.

[LotusPilot]

Brake Light Switch now replaced.  It’s now a wait-and-see if I have a solid remedy - or a simply a £65 “spare” switch 😐

For those that may be interested, the switch that came out has three GM part numbers molded into its casing: 09 132 299 / 09 175 172 / 09 175 185.

Further research shows that the first-stage contact signals the ECU to disengage cruise control (and, presumably, is used as a logic-input to the “brake throttle override” function now present in all EU homologated cars).  The second-stage contact directly feeds the brake lights - and provides the logic input to the ABS Controller (triggering the ABS pump to high pressure - so as to support the many available ESP interventions should they be required).

Many thanks for your combined input and suggestions.

Edited October 24, 2018 by LotusPilot

[LotusPilot]

Update on my TC warning - following change of the Brake Light Switch, the DPM drop-out issue has not recurred!

I’ve tested the old switch and cannot electrically or mechanically find fault with it.  My only conclusion (speculation) is that whilst there is nothing obviously wrong, something odd is occuring with phasing of the two pairs of contacts.

[ramjet]

Is it possible that the first pair of contacts on the switch, which are presumably meant to stay 'made', go 'unmade' as pressure increases on the contacts as the switch moves along to 'make' the second set of contacts?

Is it possible that could be happening and so confusing all the electric whizgidgery?

[vd9]

I had the same issue, which seems like it was resolved in B&C recently. In my case stated reason was that steering wheel position sensor calibration was off by 12° (a bit of a mystery to me how could that happen in first place) 

Edited November 4, 2018 by vd9

[LotusPilot]

“Is it possible that the first pair of contacts on the switch, which are presumably meant to stay 'made', go 'unmade' as pressure increases on the contacts as the switch moves along to 'make' the second set of contacts?“

 

Actually, it is more likely that its the other way around with the second set of switch contacts becoming make before break - instead of break before make.

The first pair of contacts (that directly feed the ECU and nothing else) are normally-closed - and open upon first pressure of the brake pedal.  The first pair contacts ensure that Cruise Control is signalled to disengage - prior to closure of the second set of contacts that (a) illuminate the brake lights and (b) provides a trigger input to the ABS control module.

Either way, behaviour would suggest that timing is causing an error condition with inputs to the ECU/ABS modules.

Now several months on from changing the switch, I have seen no recurrence of the fault.  Result!

 

Edited December 30, 2018 by LotusPilot