rb77719

My fuel gauge registers only 3/4 full when the tank is full to the brim during a hot day for a 1993 LS400. Also, for the same full tank during the cold months, it took awhile for the fuel gauge needle to get up and if it does it only got to 1/2 Full!

I search the forums as well as making a trip to our local library. I can only get to a 1994 Mitchell handbook. This service manual tells me to check the entire fuel gauge system as follows:

1. Check the fuel gauge sending unit
For a 1994 LS400. the resistance for the fuel sending gauge at E should be 4.6 Ohms, 1/2 Full 2.4 ohms and E at 0.3 Ohms.

I check mine while sending unit is still mounted and got 248 Ohms at full tank!

2. At harness side of sending unit connector, connecting a 3.4 watt light bulb between terminals 1&3 and the fuel gauge should indicate full and bulb light should come on.

In my case, I just used a single continuity tester. The bulb was lit, low fuel warning light came on but the fuel gauge needle just stayed at "E". I waited for about a minute and still nothing changed!

Question:
a. Anybody with a 1993 LS400 service manual and can share what the fuel sending unit specs are at the "E", "1/2" and "Full" locations.

b. Why is it if both tests failed, the needle is still going up although it does not accurately reflect the amount of gas I have in the tank?

Thanks!

tn52

I got the same problem here - needle not showing the correct fuel level. Since the fuel sending unit (in the gas tank) is not very expensive and I thought of it as the prime suspect, I went ahead buying a new unit to replace it but it did not resolve the problem. I now think there is another "fuel module" behind the dash that I will need to replace. From my reseach, Toyota/Lexus does have this problem quite often (not as often as the tach & speedo needles not moving). For now , I have to rely on the trip meter to monitor fuel.