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Fuel Gauge problem Posted by Gene N [Email]  (#1094)  [Profile/Gallery]
(more from Gene N) on Thu, 5 Aug 2021 18:33:16
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My fuel gauge started acting up on my 2002 Aero with 175K miles, so I figured I would replace the fuel pump and be done with it. The new fuel pump sensor worked just like the old one! A full tank shows 1/8 on the gauge and anything less than 3/4 of a tank sets the fuel low light on. I checked the tank sensor resistance and it was 420 Ohms with a full tank, which was within specification. I checked the old pump and it also showed a smooth change between 50 Ohms to 425 Ohms when moving the float manually. Must be the gauge? The Tech 2 has a test setting that allows you move the gauge electronically. The MIU (the gauge cluster) had no problem moving the needle from empty to full, and the MIU thought the tank had 13 liters instead of the 70 liters that was actually in the tank.
I went back to the pump and checked the resistance on the one wire that is grounded at the MIU. It showed a couple of Ohms to the shell on rear seat power socket (cigarette lighter) which seemed right considering the long path the signal goes through. Checking the voltage on the other sensor wire showed 10.5 Volts, also reasonable based on the assumption that circuit works on a voltage divider principle. One WIS diagram shows that the internal circuit in the MIU has a 1100 Ohm resistor connected to the B+ line in series with the fuel sensor resistor. An A/D converter measures the voltage and sets the fuel gauge. Tapping into the circuit with the plug reconnected to the pump showed 0.5 volts where as it should be slightly under 4 volts for a full tank. Working backwards it appears that resistance between the MIU B+ and the pump is 10 times what it should be.
If you are still with me at this point, my next step its to check and clean the connections in the circuit measurement wires. It is not a break in the wire because I get voltage at the pump. It is also unlikely that it is a short for the same reason. There is one connector near the A-pillar and a connector on the back of the MIU. I haven't had the time to get into it, but how hard to get to these two connectors? While the WIS is kind of vague about the connector's (H80-1) location, the MIU plug is on the upper rear of the gauge cluster. My question is, how hard is it to access the gauge plug? Can I reach it without completely disassembling the the dash as described in the WIS, or that pretty much how it goes?
I'm open to any suggestions.
->Posting last edited on Thu, 5 Aug 2021 18:39:52.
, Thu, 5 Aug 2021 18:33:16 <-- Viewing This Message, Sat, 7 Aug 2021 12:25:42
1, Mon, 9 Aug 2021 10:08:28
, Tue, 10 Aug 2021 05:17:01, Tue, 10 Aug 2021 05:37:50
, Mon, 9 Aug 2021 16:03:49, Fri, 6 Aug 2021 05:06:21
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