Discovery td5 SLABS Earthingpoint

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Been left foot breaking the second you just tap pedal it kills the TC instantly but light remains for a couple of seconds

It is not unusual for the TC light to stay on for 1 or 2 seconds after TC deactivation. Sometimes it's hard to say for sure when you'er not doing the testing yourself but from what you say, I'm confident that the SLABS ECU is working as it should, i.e. break pedal down and TC off.

At this stage, I would check the brakes and make sure they're not binding and slowing a wheel down.
 
I strip the brakes down once a year did it a few mths back
Plus checked them when had wheels off over last few days
So brakes spot on
Just done about a mile had about 8 Tc activations light only came on once right at end explain that one 1-7 no light number 8 light on home I more
 
Just done about a mile had about 8 Tc activations light only came on once right at end explain that one 1-7 no light number 8 light on home I more

Sorry I did not realise TC was engaging without TC light coming on. Hard to explain what's happening except that it looks like the ABS modulator is acting without command input from SLABS until one or more wheels slow down to a point when SLABS realises (from the speed sensors) that there's a difference in wheel spin, at which point it activates TC. This is when the TC light comes on since it is controlled directly by the SLABS ECU.

Does it always happen on the same wheel or set of wheels ? Can you do a live data capture on all wheel speed sensors and compare the output ?
 
For NPG
All I can tell is what it does is very random no particular wheel sets it off
Drive down ruff farm drive it don’t react
Tc light mainly comes on but not all the time
For everyone
Unplug sensor given up for now
Going on holiday Wednesday don’t want it putting brakes on while I am towing
 
Could I pull fuse FL11 sooner than unplug sensor and not be causing further issues
Located under bonnet engine compartment
 
If you want to kill the TC remove relay R10 just be aware that what ever you do to bring on the 3 amigos the ABS will be disabled too then when you reactivate the system erase the fault codes
 
For NPG
All I can tell is what it does is very random no particular wheel sets it off
Drive down ruff farm drive it don’t react
Tc light mainly comes on but not all the time
For everyone
Unplug sensor given up for now
Going on holiday Wednesday don’t want it putting brakes on while I am towing

Very odd and I personally never came across something like this before. But given that you have the skills and the tools, I don't think you should rush and start replacing components without understanding what's going on. I would take live captures of the relevant parameters and correlate the data with the symptoms you observe at any particular instance. I would also ensure that connectivity between the SLABS ECU, the ABS modulator and the ECM are 100%, including the terminations to ground. Also, here's some additional info re. the operation of the TC light. Have a good holiday.

TC Lamp.JPG
 

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Unfortunately that document is too generic without enough clarifications so if you dont know how the system works in reality you might overcomplicate things, for example in that "summary table" they should have mentioned when the TC comes on alone and when together with ABS or part of 3 amigos cos the only case when it comes on alone is the last line also it's not mentioned that it doesnt come on with CDL on facelifts. The statement with the pressure build-up is the strangest cos there is no sensor to monitor the system's pressure.
 
Unfortunately that document is too generic without enough clarifications so if you dont know how the system works in reality you might overcomplicate things, for example in that "summary table" they should have mentioned when the TC comes on alone and when together with ABS or part of 3 amigos cos the only case when it comes on alone is the last line also it's not mentioned that it doesnt come on with CDL on facelifts. The statement with the pressure build-up is the strangest cos there is no sensor to monitor the system's pressure.

The info only shows the events when SLABS activates the TC lamp, as this was the topic of the conversation. Of course, drill down on specific faults would require decoding lamp status combinations involving ABS, HDC, EBD & TC and this I believe is clearly shown in RAVE. As for CDL, the article is from a pre-2002 document, hence why the TC lamp behaviour for the facelift model is not covered.

Good point on the lack of pressure sensor and thus how SLABS could possibly monitor the pressure build up. I can only surmise that SLABS is doing this by monitoring the voltage or current variations supplied on pin 8 C0504, which is directly connected to the ABS pump positive terminal. Increased fluid pressure = increased load and therefore more power supplied to the pump.
 
The info only shows the events when SLABS activates the TC lamp, as this was the topic of the conversation.
What i meant was that IMO it's exagerated to say that the SLABS activates the TC lamp in other than the last line cos all the other cases are 3 amigos so the ECU activates all the ABS related lamps not just the TC and once ABS/TC with CDL... and afaik the topic of the conversation was about the erratic TC behaviour not about why the ECU activates the lamp:cool:
I can only surmise that SLABS is doing this by monitoring the voltage or current variations supplied on pin 8 C0504, which is directly connected to the ABS pump positive terminal.
IMO the correct way to put that is that C0504-8 is connected to FL11(30A) through the ABS relay's contact to monitor if the pump gets feed or not, it cant pick up current or voltage variations on that path as the pump is in parallel to earth on that wire. If you look to "electrical data" table in RAVE the only monitored part on that path is the relay's coil resistance, the pump's resistance is not mentioned
 
.. and afaik the topic of the conversation was about the erratic TC behaviour not about why the ECU activates the lamp:cool:

When I said this was the topic of the conversation, I was referring to the conversation I was having with Mark at that particular moment (posts #45 & #49) and was not a reference to the core topic of this thread.

IMO the correct way to put that is that C0504-8 is connected to FL11(30A) through the ABS relay's contact to monitor if the pump gets feed or not, it cant pick up current or voltage variations on that path as the pump is in parallel to earth on that wire. If you look to "electrical data" table in RAVE the only monitored part on that path is the relay's coil resistance, the pump's resistance is not mentioned

It is true that the pump and SLABS are wired in parallel on a shared positive rail and a common ground and in theory, SLABS can operate the pump without ever activating the pump relay (although I'll be surprised if this was the case but it's possible). The point here is that if this was a pure resistive circuit, I would agree with you but the pump is an inductive load and there are ways how it could be monitored and variables such as load and speed deduced from the current and voltage characteristics on the circuit. For instance, if Pin 8 C0504 is connected internally to a capacitor and a resistor, SLABS can monitor the variations in the charging & discharge current across the capacitor, which are influenced by the current going through the pump and therefore torque. Likewise, the fly-back voltage or back EMF released on the parallel circuit once the pump is stopped gives a good indication of the load on the pump just prior to being disengaged (back EMF decreases as load increases).

Like I said earlier, I can only surmise that this is what could be happening, thanks to the lack of any direct means for the SLABS to measure fluid pressure. So unless confirmed somehow, it remains a theory. Alternatively this could be one of those rare slips in LR's documentation. There are WABCO ABS units with internal pressure sensors and IIRC, the P38 is equipped with one of them. So maybe wires got crossed at some point in the authorship of the technical literature, who knows ?
 
Sorry if this has already been suggested, but have the sensor wires been traced back all the way to the SLABS ecu? If one of them is intermittently grounding out then I expect that might cause the TC to kick in. Just a thought.
 
If its driving you mad, replacing a few components may be worth a stab. A used 03 slabs ecu is cheap second hand and at the same time you can clean all contacts and check the wiring under the glovebox.
 
Sorry if this has already been suggested, but have the sensor wires been traced back all the way to the SLABS ecu? If one of them is intermittently grounding out then I expect that might cause the TC to kick in. Just a thought.
No Ben, that would bring on 3 amigos right away.
 
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