They changed the system some what from my 89's, but I believe the
main logic is the same.
The module checks that it is receiving a signal from all four sensors, if
one, two, or three signals are missing - it prompts the Service LTPWS
alarm. However it still should check for low pressure from any working
sensors. How low was the pressure in the tires that were low ? I could
be accidental that you found two tires low.
You could try lowering the pressure in one tire to below 25 lbs, the system
should set Low Tire Pressure alarm in a few hundred feet. If not, then
re-inflate the tire, and lower another tire, repeating the test.
Does your system indicate which tire is low, or just say
Low Tire Pressure ? Your manual should tell you this.
If it doesn't indicate which tire then it may be the same as my '89's.
I had a similar problem when I first got the card used in '98.
In the end I removed all sensors from the wheels, and tested each one of them individually
to see which one(s) actually worked. I found two bad sensors.
You start the engine, then hold the sensor in your hand, and rapidly
smack it against a hard object (brick, etc.) after about 30-60 seconds
the Low Tire Pressure alarm should come on (there's no pressure when
the sensor is not inside a tire). Repeat for each sensor until you find the bad one.
HTH LOL