If your BMW 2002 fuel gauge becomes erratic or finally reads completely "E" (all the way down below the red), chances are the tank sending unit (fuel probe) has failed. The replacement/repair cost can easily exceed $5100 if performed at a BMW repair facility.
Experience with my 1971 BMW 2002 has shown on two different occasions over a seven-and-one-half-year period, that the probe can be easily repaired to last many more miles and save lots of money. The defect is usually a break of the resistor wire in the probe at one of the two solder connections.
Caution: if you attempt to replace or repair the fuel probe make sure all smoking or spark producing material is kept away from the work area during the maintenance process.
- Gain access to the fuel tank by removing the right-side trunk floorboard. If an ohmmeter is available, check continuity between the two fuel probe wire connections. It should read somewhere between 0-75 ohms depending on the fuel remaining in the tank with the wires disconnected. If open, proceed to step 2. You have a defective fuel sending unit.
- Remove and cap fuel hose from the sending unit. Remove the two wires (remembering the hookup), if not previously done.
- Turn fuel probe top approximately 1/8 of a turn counterclockwise (tap with large screwdriver and hammer) and slowly lift probe out of tank to allow possible draining. Save rubber "O" ring for later reinstallation. Temporarily cover the open fuel tank with a clean rag to prevent contamination.
- Remove mesh filter from bottom of probe. It pries out. Unscrew small nut on bottom and remove outer aluminum casing.
- This allows visual inspection of the probe interior. You can see the float assembly, the end piece spreader/tensioning device and the actual resistor-type wire which is as fine as a human hair. The wire should be taut from one contact to the other running parallel along the center post and over the end piece tensioning device. It forms a loop along which the float slides up and down, varying the resistance with different fuel levels. If the float is all the way down you read maximum resistance: 75 ohms (fuel tank indication = RED/EMPTY). Float all the way up: minimum resistance, tank is full.
- If the wire is in fact broken at one of the solder connections, unscrew the small nut from the center post holding the wire spreader/tensioning device. Remove it and the float assembly.
- Repair and resolder wire to the proper connection, insuring that there are no kinks in the fine wire. Reinstall float mechanism and insure the newly repaired wire runs properly on both sides thru the float contacts. Gently keep wire loop taut during re-assembly to prevent kinking. Reattach plastic end piece spreader/tensioning device and secure with small nut. Pull wire carefully over the plastic end piece spreader/tensioning device and insure that it lies in the proper groove and does not touch the center post.
- Reinstall outer aluminum casing and secure with nut. Reinsert bottom probe mesh-type filter and slide rubber "O" ring over the probe.
- Reinstall probe into the fuel tank, with hose spout pointing toward the one o'clock position. It should take approximately 1/8 turn clockwise. Attach hose and wires. Clean up work area prior to check-out (residue fuel).
- Install trunk floorboard.
Author: Menko D. Christoph