Contour Enthusiasts Group Archives Forums General Troubleshooting ABS light comes on when HVAC is set to defrost

I have a strange problem on my 96 SE. Sometimes when I turn my HVAC to defrost my ABS light will come on. This only happens when I turn it to defrost, not defront/floor or passenger or pass/floor etc.

When I turn it to defrost there is also a noticable draw of power from the dash lights. (Again only in defrost) It happened to me yesterday and the way home from work when it was snowing bad (wet snow) but 6 hours later when it had stopped I could not reproduce the problem.

This doesn't happen all the time. It only seems to happen when it's wet outside or driving in snow + the defrost is on. If I have it on any other setting and it's wet out everything is fine.

Is there a short somewhere? Are these systems connected in any way? Could it be the alternator?

I'm really puzzled. I was driving in the snow and slush again today and everything was ok...

Any ideas?

  I've had a similar problem.  See this thread.  More questions, than answers, I'm afraid.  What I do know is that there is something in my ABS system that gets wet, and when it gets wet, if the A/C compressor is engaged (as it in in either the A/C or defrost HVAC positions) the ABS fails.  After a few days, the component dries out, and everything is fine again.  What the A/C compressor has to do with the ABS, or with this failure thereof, I do not know.

Have you received the recall notice for the underhood wiring harnesses? I had problems some time ago with my ABS and TC lamps going on/off so the dealer changed the LF harness after working on it for a week and the problem went away. A couple of years later, I needed the underhood harnesses changed because all the insulation was falling off. In the process of doing the work the mechanic blew up 2 ABS units. My ABS unit is a newer model, doesn't make that self test sound and reacts far better than the original.

I had this problem too. My solution was to remove the ABS light from the dashboard because Ford wanted $4000 Canadian to fix it. (replace all ABS wiring and module).

Since then, my ABS seems to have been working properly, but I haven't put in the ABS light again.

My theory on this is that the ABS module needs a constant voltage on a certain pin. If this voltage drops below the amount it needs, then the ABS light comes on.

When you put on your A/C, then the voltage drops below the threshold and the ABS module freaks. For instance, the radiator fan runs when the A/C is on. Maybe this causes the drop in voltage.

Anyway, I think the wiring on our old cars is poor and there is too much resistance somewhere. This causes the voltage to drop when the current draw is high in a particular circuit.

If you are under 100,000 miles, then you qualify for replacing the wiring in your engine compartment under recall, as long as Ford determines the wiring is bad. I have way higher mileage, but give it a shot. Many problems have been solved by replacing the wiring, but it is expensive and time consuming to do it when not under warranty.

- Randall

I have only just picked up this thread but, If your car has automatic seatbelt tensioner,which most have and certainly mine does, which operates on air bag activation, just check your connectors below your seat, after a passionate encounter and my seats right back I had this problem, Ford wanted to replace the seat belt tensioner, all I did was pull the connector apart and then back together, never played up since, I really hope this sorts your problem.


Neil

One other thing to check is the battery. This sort of plays into the theroy of too much resistants in our systems. I recently replaced my battery and it solved all sorts of problems. There where no real signs that it needed to be changed, other then sounding weak when cranking in the morning.

When driving in the rain, my Air Bag light would flash a code of 53, which means (I think), the system detects a short in the passenger side circuit. Also, my sunroof would not return to the closed position when the key was turned off. It would mearly close, then open again then close, then open and stay open. There is a funny story to this, but I wont get into this now. Also, the most noteable fix was that when the compressor would kick on, the dash lights would dim quite a bit.

*After typing all this, I wonder why I did not change my battery sooner!*