Question Re TIB for ABS/HDC/TC troubleshooting

[Blue Meanie]

Hi Guys,

I'm one of the many with the 3 Amigos problem, so I was going through the procedure outlined in the LR tech bulletin (No. 70/07/04/NAS) to try to track down the problem. But it seems to contain a mistake to me so I thought I'd better check with more experienced types.

Steps 11 - 14 describe how to check the resistance at pin 9 of the connecter that plugs into the ABS modulator, and step 14 says if this is out of spec, then the modulator should be replaced.

But isn't it the signal going INTO the modulator from the SLABS that is being measured? Why would you replace the modulator rather than go looking upstream at the SLABS?

[stevo]

no it is correct there is two switches inside that have an enternal resistors fitted the resistance changes with pressure applied by the brake pedal, you can get the switches for around $120 do a saerch on shuttle valve switches and 3 amigoes I have repaired two modulators with different faults, do a search under shuttle valve switch or 3 amigoes. you will get all the info you need plus pictures on repairs.

[Blue Meanie]

Thanks for your reply Stevo,

I've actually done an awful lot of searching on this over the last couple of years, and I have had the shuttle value switch replaced. But to no avail. Hence I thought that I would check all the wires and connections myself, just to eliminate that possibility.

But the reason for my question is this: If we wanted to check those resisters in the modulator, then it would seem to make sense to measure the resistance at the pin on the side of the modulator (male side of the connection). I've done this - no effect when the peddle is pushed. However, the TIB instructions say to measure the resistance at the pin in the connector (ie female side), and here you do get a change in resistance. But that wire isn't connected to the modulator (its unplugged from there), it goes to the SLABS. Hence my question about whether it is really the modulator that is being checked by this test.

[astormsau]

i had the issue with the bad solder joint where the shuttle valve plugs into the abs modulator body. it didnt really show itself with a multimeter and banging the modulator around. i would suggest bypassing the modulators intternal wiring and running the connections from the modulator straight to the factory loom with an inline connector in the middle so the modulator can still be removed.

Andrew

[stevo]

it is the modulator side of the plug that you are testing and Andrew that is also a good way of fixing the problem and easy to do aswell, the problem with most of these faults is they are intermintant so can be a PITA to track down, where do you live some one might be close enough with a nano or rova com to down load faults

[Blue Meanie]

Thanks for the clarification Stevo. I wasn't getting any change in signal on the modulator side so I figured the TIB must be referring to the other side where I was getting a change in resistance (the numbers aren't in spec but that's not surprising).

Regarding reading the faults, I've just got myself a Nanocom - that's really why I've started looking at this again - I was hoping to use it to figure out when the fault occurs.

Andrew, sorry to be dumb, but I don't get "running the connections from the modulator straight to the factory loom with an inline connector in the middle so the modulator can still be removed". Could you explain what you mean? Thanks muchly.

[stevo]

I think what he means is instead of plugging the shuttle valve switch into the plug that is inside the modulator bypass this connection by bringing the plug to the outside of the modulator and connecting one of the wires to the wire that goes to pin nine and the other wire to ground or slice this wire to any of the following pins 3,6,7,8, all these go to earth.

Check out the circuit diagram http://www.wabco.info/intl/drw/5/5080.pdf?PHPSESSID=d44ef7ba5190ce8c316ccebbd2ceced 1.

Follow from pin nine with foot off the brake pedal current flow is through the four resistors,slight brake pressure will activate one of the switches and current flow is through 3 resistors and abit more pressure will close the second switch contacts and current will flow through 2 resistors only.

[Blue Meanie]

Thanks Stevo, that's great.

Any idea what the SLABS ECU is actually monitoring that causes it to post a shuttle valve switch fault? Is it just connectivity through that circuit, or does it actually monitor the resistances? And is it only that circuit?

[stevo]

connectivity for sure but would suspect if the resistance is out of spec's it would also show a fault aswell, I have pulled a switch apart that was full of rust and was giving intermitent readings looked fine on the outside but the inside was rusty, there is pictures on this site somewhere from my previous posts on this subject.

The pins on the inside of the modulator where they are soldered to the circuit board can suffer from a lack of solder mine had this and someone overseas on another site has also had the same fault.

[Blue Meanie]

I think you're right about resistance being monitored too - it would make sense to have that if the correct functioning of the system relies on that being in spec. Probably not any of the other curcuits going through that connector though (controlling the input/output solenoids) as then "shuttle valve switch" would be misleading. Good-Oh, that limits the possibilities.

The fact that I've already had the switches replaced means its more likely a cruddy connection. Had a prang a while ago, and that fixed it for a few months, so again, something a bit loose is indicated. The prang option is a bit extreme (and doesn't last anyway), so I'll have another wiggle of the wires this weekend and perhaps try the by-pass option.

Thanks for your help, Steve.

For others following this, I've put a cross-reference below to the ALRO collated wisdom on the topic (including some of Stevo's earlier emails he referred to):

http://www.aulro.com/afvb/good-oil/34321-electronic-driver-aids-including-3-amigoes.html

[Blue Meanie]

Just an update on this: I performed a double by-pass on the SVS circuit yesterday and it seems to have fixed the problem (to early to be sure but we live in hope). The earth pin on the underside of the modulator that the SVS connector pushes onto lost connectivity if I pushed directly on it. It didn't wobble and I couldn't feel any movement "into" the modulator body when I pushed it, but the resistance went to max every time I did it, so I'm fairly convinced that was the problem. So now the SVS wires are extended out from under the modulator and spiced into the 8 and 9 wires in the loom. Fingers crossed that the 3 amigos are finally beaten.

Thanks for all your help Steve and Andrew.

And of course the Nanocom (or similar) was essential to be able to bleed the modulator after it went back in.

[stevo]

to see you (hopefully) had a win but would be willing to bet that is the problem