1994-2002 [Subscribe to Daily Digest] |
In my opinion the coolant low sensor is the most valuable warning there is in a Saab 900. If you have a burst radiator hose and the there is a quick dump of coolant the temp sensor could be in hot air and not register correctly. So a working low coolant light gives the first indication of a burst pipe. Well, we all know you cannot drive far without coolant. Some people ignore the light, remove the lamp or even jumper out the sensor.
The main problem people cannot justify buying a coolant reservoir with the sensor attached. I was confronted with this and decided to repair the sensor. The first thing to do is short out the flying coolant sensor lead to confirm the sensor light goes out. Even drive with this shorted for a couple of days to confirm it’s a sensor problem.
Remove the sensor from the reservoir tank – done with a couple of very fine bladed screwdrivers. When removed cut with a very fine jeweler’s saw around the junction of the white cap and the black body of the sensor. The saw will go though the long sides but on the ends you will cut slightly into a printed circuit board. When you prise off the cover you will revel a small glass reed contact. This will probably have high resistance contacts which will bring on the light regardless on the correct level.
With the reed switch exposed do some measurements with a multimeter – Use a magnet to test the action of the reed switch. If the reed switch is faulty then a replacement can be purchase for a few cents. When soldering in it is very hard to bend the reed switch leads with out breaking the glass envelope. What I did was cut the leads very short and wrap some fuse wire around the short lead and bring the ends through the printed circuit board and then solder. While the reed is exposed it’s a good idea to check continuity from the reed switch ends to each connector contact pins. If one or both are open circuit or high resistance the pins soldered to the PCB may have a dry joint or cracked.
If there is a problem with the pin connection you can cut the sensor body. Again with a jeweler’s saw you should cut around the bulge but not straight through. This exposes the pcb where the contact pins are soldered – re solder and check again.
Now it’s a simple matter of putting the cut pieces back in with a dollop of RTV to hold and seal into place.
This is what I did to mine a 4 years ago and it’s been 100 percent.
Cheers – Martin Barnes (New Zealand)
97’ Saab 900s Talladega 2.3NA 167,000Kms
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