There are several ways the Fuel Gauge Sender (sending unit) can fail. Internal parts can wear out and break but sometimes the windings just get dirty and need to be cleaned. New replacement fuel gauge senders are no longer available. The following should help assist you in troubleshooting your sender.
If your car sits for long periods of time varnishes and other contaminates in the gasoline can build up on exposed areas of the resistance wire windings and the wiper that slides across them. When that happens erratic fuel gauge readings and complete in-operation of the fuel gauge can result.
If you suspect your problem is caused by the car not being driven you should try filling the gas tank half full and add some Sea Foam Motor Tune - Up fuel system cleaner to it. Then drive on a curvy road for a while. The sloshing of the half full tank of gasoline with the cleaner in it will cause the wiper to do a lot of moving across the resistance windings and possibly break any buildup on the parts loose so they can start making good contact again. It may not correct your problem but it is worth a try before removing the gas tank to access the sending unit.
If your fuel gauge stops working suddenly while routinely driving your car, the problem is likely to be more than just contaminants built up on the resistance wire winding or wiper. Trying the Sea Foam in the tank as described above might still be worth a try. It is more likely that your problem is related to a bad connection, a bad fuel gauge sender in the tank, or a bad BCM.
You can do some testing before removing the fuel tank to help determine the source of your problem.
Back at the tank there is a three wire connector going to the sender. You will need a Digital Volt Meter to check for 12 volts in the following tests. See section 8A-82-13 (1990 service manual)
With ignition in RUN position. Check the following:
- Check the Pink/Black wire to ground....................... should have 12 volts
- Check the Pink/black wire to the Black/white wire.... should have 12 volts
- Check the Pink/black wire to the purple wire.............should have 12 volts
According to the service manual:
If test 1 or 2 show an open circuit - The problem is the sending unit inside the tank.
If test 3 is bad - The problem is the a bad Body Control Module (BCM).
The fuel tank must be removed to gain access to the fuel gauge sending unit parts that are shown in the photos below.
Below is a photo, #1, of the sending unit that has markings added to help visualize what you can't see inside. It is not difficult to see why it might have problems. It is a very complicated device. The tan curved part at the top covers the resistor windings. Note that it is held in place with two screws and there are two screws that are used as spacers and are also part of the electrical circuit. The connectors I have seen always look marginal.
Photo-1
Photo #2 below shows the tan housing and the resistance wire wrap, if any of those wires are broken the gauge will not work. The tan part seems to be common on several GM cars. You should be able to find a good one in a salvage yard and install on your sending unit if a bad resistance wire winding is the cause of your sender problems.
Photo-2
The next photo, #3, is of the wiper that rubs against the resistance wire wrap. Common problems that can occur with the wiper are:
- The little finger on the wiper can be broken/damaged
- The back side, which rubs against a conductor and the little tabs can be broken.
- The contacts on the wiper can be broken.
(Read more about this and how to repair below)
Again you can make a wiper work from another GM car of the same vintage. Riviera, Toronado, Seville, and Eldorado all have the same parts but the entire unit will not usually transfer to the Reatta. Other GM cars may have parts that will work.
Check the Reatta Parts Vendors page on this website for reputable vendors who may have these parts for sale.
Photo-3
The following repair should only be done as a last resort when the parts needed to replace defective parts can not be found.
The wiper that contacts the resistance wire wrap, shown in the photo below, is a one piece stamping and very thin on the pivot end (where the float rod attaches). It also has a wiper to ground. They are very prone to breaking.
Photo-4
The contacts that are common to break off are shown in the photo above on each side of the shaft. Because they are thin and small, they will corrode and break off.
It is possible to repair the wiper assembly using a length of wire placed over the wiper assembly. Take the finest (smallest) wire that you have and wrap it around something that is about 1/2 inch in diameter (a sharpie pen works well). Make about 3 wraps. Solder one end to the wiper and the other end to the brass that the broken contacts touched. The fine wire with wraps allows the arm to swing freely but give the contact you need.
Thanks to Barney Eaton for supplying the photos and most of the information for this article.
