Question about 1993 Saab 900
First you need remove the floor panel in the trunk, then pop out the
smaller plug you see on the right side of the car. this one is all
rubber, the one on the other side is metal with a rubber ring. Under the small plug you will find a plastic ring holding the sending
unit into the gas tank. use a hammer and a plastic handled screwdriver -do not strike metal on metal when you are opening your gas tank- to
remove the lock ring and the sending unit.
Be careful not to break your electrical connection. I find it easiest to remove this first and tuck it forward, out of the way. Best place to start is the top of the fuel level sender under the false floor in the boot/trunk space. When you remove the second bit of the false floor you'll see two covers - the large one (metal with a rubber surround) on the left side of the central chassis rail is for the fuel pump, and the smaller one on the right side (just plain rubber like a CV boot) is the cover for the fuel level sender. There will be small group of wires coming out of the fuel level sender cover.
If the fuel gauge needle never does anything, it's quite likely that the wiring to/from the fuel level sender needs checking (which would normally be just connections at the sender that need fixing) or the fuel level sender itself has died.
The sender in your car should be the type that is formed from a metal can with a plastic top as on the very earliest c900's with a white plastic body level sender, the needle of the guage stays at full if the sender gives no signal! With the later metal-can senders, the fuel gauge always give a zero reading with no signal from the sender.
Depending on the year of the car, there will either be a small 3-pin connector with two parallel pins and one at 90 degrees to the other two, or a larger 3-pin connector with three round pins.
First thing to do is check that none of those connections are loose or completely disconnected. It's possible the connector could have come complete away from the top of the sender, esp if it's the '2 parellel pins + 1' version.
The earth connection for the fuel level sender (black wire) should run to the rear earth point right at the back of the central chassis member so you can easily check that for continuity with a multimeter as the back part of the central chassis member is exposed any time you lift the false floor to check the spare tyre, etc. If the earth connection to the plug for the fuel level sender is broken, that'll need repairing.
The other two wires are the graduated signal for the fuel gauge needle, and for the on/off functioning of the 'low fuel' indicator light. I think they are brown and grey but don't quote me on that.
If you check out all of the wiring at the top of the fuel level sender and it's ok, plus the ground connection is fine, the next thing to consider is the sender itself. On the metal-can senders, it's not uncommon for them to fall apart inside the tank when the thin stainless steel shaft holding the top and bottom parts of the sender body together breaks at the end of the top threaded part of the rod. That shaft is also what 'guides' the float inside the sender and if the bottom cap of the sender comes away, the float has no stop and will drop off the shaft if the shaft itself hasn't broken at the top. The metal can body will also fall off and you'll look at the top of the sender secured by the big plastic 'nut' and think it's fine, then undo the holder and lift out just the top part of the sender perhaps with some of the metal shaft still attached.
Don't worry though - there are often used senders and sometimes new ones listed on the Evil Bay. I think it's just that due to their environment (sitting in fuel all the time) eventually the materials start to weaken, and over a long period of time there is a LOT of vibration that the fuel sender body copes with, plus the undampened forces applied by the body of fuel moving around during normal driving, which adds up to put a fair bit of stress on the stainless steel shaft. It's threaded at both ends and where the thread stops (esp. at the top end) is the weak point.
However, if the sender is fine, and the wiring is all fine, you'll need to trace back the wiring to gauges and see if there might be a fault there, and if nothing, you might need to disassemble the dash to remove the gauges and replace the section with the fuel gauge in it.
Check all the other stuff first though (wiring and the sender itself).
Hope helps and good luck.
Posted on Jul 27, 2010
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Posted on Jan 02, 2017
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