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post #1 of 5 (permalink) Old 02-02-04, 08:00 AM Thread Starter
Join Date: Feb 2001
Location: Bibra Lake Western Australia
Posts: 3,320
Odd SLS Problem

Ok I have been struggling with this one for a few days. The self levelling suspension on the NB Fairlane has been playing up. After running the self diagnostic test and some soapy water spray checks I found the rubber bellows on the rear monroe air riders were perished and leaking. On checking I found I replaced them last 10 years before so didn't feel too bad about buying another set at $285.

After fitting the new set of shockies I had no leaks and a better ride but some ongoing problems:

a) The self diagnostic test will only run once with no error codes. After the first successful test subsequent tests fail with the single flash error. If I leave it half an hour it will pass again just once.

b) On hot days with three or more passengers it will come up with the check suspension warning light (and won't reset - if we stop turn the engine off and wait 30 seconds a few kms down the road it will start flashing and beeping again). On cool days or with a light load it seems OK but I guess I need a few more days testing before I am sure.

I have done all the pin point tests and tests A, B, C and D in the Ford factory manual and they don't find anything wrong.... I think.

The manual is a bit ambiguous but it seems to imply that with the height sensing module unplugged a test at pin one on the module socket (not the plug) should show continuity with earth but it doesn't. I have opened the module and see no way that the circuit earth or pin 1 can be earthed to the case or the car chassis except via the harness plug (pin 1 on the plug is earthed and passes a chassis continuity test). The case is plastic except for one side but the screws retain that metal plate screw into the plastic case and the PC board is screwed into the bottom of the plastic case. Does anyone know off hand if indeed pin one on the module is somehow meant to have it's own earth when the module is unplugged? Anyone got any other ideas on the cause of this strange behaviour?

The self test and pin point test show the vent solonoid, compressor and compressor relay is OK. On the first test the compressor will pump up vent and pump up again. It seems to me that perhaps the module isn't switching the vent solonoid open to self vent or lower as it should which suggests either a faulty module or perhaps poor connections between the module and pins on the harness socket. I have tried a new relay and circuit breaker (fuses) with no change.

I also do not always get 12 volts on pins 2 and 3 on the compressor harness plug (0 volts instead) but I thing this is a result of the self diagnostics finding a fault.

I guess my next step will be to test pin one on the module on my other Fairlane (the NC) and then try swapping the modules between cars.

PS I like the SLS systems and so far the have performed well; so no need for suggestions on reverting to non SLS suspension please.

Regards Blue

Last edited by Aussiblue; 02-02-04 at 08:09 AM.
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post #2 of 5 (permalink) Old 02-07-04, 09:01 AM Thread Starter
Join Date: Feb 2001
Location: Bibra Lake Western Australia
Posts: 3,320
Re: Odd SLS Problem

I think I may have solved it. I think I have a marginal battery. I noticed the dash lights faded when the compressor ran and a test of the cells with a hydrometer shows all cells are about half charged and two are flat. It just met a load test after charging but wasn't holding a charge after being left for just 15 minutes. It seems the battery could run the compressor for 1 or 2 self tests but that's all. I guess we'll see if a new battery fixes it.

Regards Blue
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post #3 of 5 (permalink) Old 02-22-04, 05:43 AM Thread Starter
Join Date: Feb 2001
Location: Bibra Lake Western Australia
Posts: 3,320
Re: Odd SLS Problem

Well it wasn't the battery. A new one didn't fix it. I also thought it might be base idle problem as it usually came up with flashing and beeping when idling at the lights with the air con on. Well that wasn't it either although it was idleing below spec (fixed that). It was getting worse and worse so the check suspension warning light was coming on more frequently. I had the control module out a few time and fitted a heat sink to the larger T0-3 trans inside but it all seemed ok. So yesterday I took the compressor out and dissasembled it and found:

a) At the some time a previous owner had lost the cover off the compressor and the tyre had worn partially through the vent solonoid feed wire. Replaced that.
b) Compressor piston wasn't moving freely in cylinder bore although bore and piston looked OK. Tried various lubricants and cleaners; engine assembly lube worked best.
c) Dryer was full of water and trans fluid (must have got some in when I flushed the trans and grabbed the inlet instead of outlet hose). Pumping air through it with my workshop compressor fixed that.

I also replaced the lost filter for the vent with a piece of scotchbrite.

Well it is now all working 100% (touch wood) so I'm not really sure which off these was the actual solution.

For those wanting to overhaul the compressor some hints:

a) You need some Loctite Master Pipe Sealant to use as a gasket sealant for the solonoid and compressor crankcase covers.
b) The "bolts" that hold the head and cylinder in place are self tappers and cannot be torqued too tight (about 5 NM) and care needs to be taken to use the old threads they have made. However, if you stuff it (like I did with one) metal cement can be used to give something for these self tappers to bite.
c) Even after lubricating and cleaning the piston is a tight fit in the bore and may see too tight.

Regards Blue

Last edited by Aussiblue; 03-03-04 at 04:35 AM.
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post #4 of 5 (permalink) Old 03-02-04, 04:43 AM Thread Starter
Join Date: Feb 2001
Location: Bibra Lake Western Australia
Posts: 3,320
Re: Odd SLS Problem

Well it came back (the problem) as soon as it got hot again but I think I have nailed it this time.

I noticed on the weekend that whenever the thermofan I added years ago came on the SLS compressor stopped. I also found that the alternator was not always charging. I pulled the blade fuses for the thermofan so I could test the current draw across the fuseholder with a multimeter and found the fuses melted but not blown. At it was late at night I just replaced the fuse. Next day the SLS continued flash its alert and when I pulled the new fuse it was also melted but not blown. As you can see the two melted fuses are almost identical.

Tests showed that the melted fuses were no longer providing a path for the electricity (the swollen nature of the melted fuse stopped the blade on that side connecting with the fuse holder). The resistance across the fuse holder with the fuse removed was between 200 k ohms and 1.3 Mega Ohms!!! The blackened and slightly rusted fuse holder was providing the path to power the thermo fan (without a fuse in place) albeit often at very high resistance and thus very high current draw. I also had a very hot but not yet fused fusible link at the battery.

I think this explains the non charging alternator, flaring dash lights and what I thought was marginal battery. Also as the resistance on the shorting fuseholder varies, sometimes things worked OK (the SLS was OK and the alternator charged).

Essentially I think when the relay (set up to cut the fan in when the air conditioner compressor is on) switched the thermo fan on the current draw was so great the compressor couldn't run. Off course most of the time when I was testing the SLS I turned the air con off so I could hear the SLS compressor running (no thermo fan or air con fan noises).

Well so far replacing the fuse holder and putting a temporary fusible link in (awaiting Ford part on order) seems to have fixed it. However, it was not hot today, and I had a few false cures so we shall wait and see before calling this a victory. In any event it is an interesting fuse fault.

Regards Blue
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post #5 of 5 (permalink) Old 03-02-04, 05:14 PM
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Re: Odd SLS Problem

Interesting thread too!

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