focuses on the saab adjustable seat heater.
This is the system that has an in dash switch with 3 temperature
settings. If you have a classic Saab 900 or a Saab 9000 model you
may have this type of seat heater. As with many electrical systems
the best way to diagnose is to get your wiring diagram out, and
find a easy to access spot that most of the circuit runs to. In
this case we will start our diagnosis at the plug for the in dash
switch. You will need your volt /ohm meter to run these tests. The
switch on your dash supplies current to a heating pad under the
upholstery of your seat, it's like the electric blanket you may
use in your bed.
get to the diagnosis I want to describe how this system works.
There are two heating pads in the seat one for the bottom and one
for the back they are wired in series. This means if there is a
break in the wiring of one heater pads both stop working. There
is a ntc resistor (this is a resistor that goes down in resistance
the hotter it gets) embedded in the lower pad to control temperature.
This ntc resistor is wired to the in dash switch/relay. Inside the
switch is a relay that switches off the current to the heat pad
as it gets up to selected temperature.
electrical diagnosis you will need the wiring diagram for your
model. With a diagram and this procedure you should be able to pin
point the problem in no time. If you have a classic Saab 900
first check fuse #12 on the Saab 9000 check fuse #10.
Remember to not just look at the fuses but make sure they are hot
with 12v with the ignition on.
thing you will do is pull the in dash seat heater switch out
to access the plug socket. When making measurement probe from the
back of the plug to avoid damaging the small metal contacts inside.
Check terminal #2 you should find battery voltage here with the
ignition on. This is the positive supply from the fuse. If this
is dead and the fuse is powered up you must trace your wiring back
to the fuse box. The classic 900 has a connector between the fuse
and switch above the hood release handle this should be checked.
Check pin #9 for ground this you will test with your ohm meter
you should have continuity from #9 to chassis ground. Near zero
ohms 1 or 2 ohms will not keep this from working. If you find no
ground trace this through the connectors to it's chassis connection
(900 this will be near the parking brake under the center console,
9000 on left front seat member).
Now turn on the switch and check for voltage on pin #10 this is
your power supply out to the heater pad. If you find no power here
you may have a bad switch or a bad ntc resistor. If in step 4 you
find the ntc resistor good most likely you have a bad switch.