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Discussion Starter · #1 ·
Just purchased a 2008 Ody with 123,000 miles. The gas gauge reads empty even after I filled the tank. I checked the fuse, and it is not blown. I performed the gauge self test, (involving the lights, ignition key, reset button, etc.) and all the gauges swept over the full range including the gas gauge. I removed the rear seats, pulled the carpet up, removed the fuel pump access panel, and unplugged the fuel pump connector. The voltage between pins 1-2 is 12 volts when disconnected. The resistance between pins 1-2 on the fuel pump module measures 20 ohms, indicating the fuel sensor is at the full position. The fuel gauge does not move off empty whether the connector is plugged in or not. I also checked the OBD with my scanner. Initially I had a U0155 error code, "No communication between computer and instrument panel, which I reset. The code has not returned, but the gauge still reads empty. Any suggestions?
 

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Welcome to this forum. No suggestions, but I applaud everything you've done so far to troubleshoot, diagnose and try to solve this issue. Good post.
 

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From the start : I am far from expert on this. If gauge itself is fine, the sending unit may be bad. There are a few YT videos on that. My course of action would be to replace just the sending unit taking the replacement part from a junk yard (reason - I really doubt that this is the kind of item that goes back often, so high chances that you get a good one. May pull the whole fuel pump assembly if they go for cheap there). If that does not solve the problem, then I would ask myself - how the level is measured. Does something has to come up/down with fuel level. Can that something be stuck (again I have no clue how it actually measures the level).
 

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Discussion Starter · #4 ·
From the start : I am far from expert on this. If gauge itself is fine, the sending unit may be bad. There are a few YT videos on that. My course of action would be to replace just the sending unit taking the replacement part from a junk yard (reason - I really doubt that this is the kind of item that goes back often, so high chances that you get a good one. May pull the whole fuel pump assembly if they go for cheap there). If that does not solve the problem, then I would ask myself - how the level is measured. Does something has to come up/down with fuel level. Can that something be stuck (again I have no clue how it actually measures the level).
 

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I have not looked at the sending unit on the Odyssey so I don't know for sure. But, most sending units I know have a floating mechanism which goes up and down according to the fuel level.
 

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Discussion Starter · #6 ·
I have now pulled the fuel pump from the tank and checked the sending unit. the float moves freely up and down, and the resistance between pins 1-2 on the fuel pump connector vary from about 21 ohms empty to about 750 ohms when full, well within the specified range. Is is possible the instrument cluster is defective even though the self test shows all the gauges sweeping over the entire range? So far I have not found a wiring diagram showing where the wires from the fuel tank connect to the instrument panel. I understand this may be through the CAN bus, so perhaps they connect to a body control module?
 

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First post:
The resistance between pins 1-2 on the fuel pump module measures 20 ohms, indicating the fuel sensor is at the full position. The fuel gauge does not move off empty whether the connector is plugged in or not. I also checked the OBD with my scanner.
The current post.
I have now pulled the fuel pump from the tank and checked the sending unit. the float moves freely up and down, and the resistance between pins 1-2 on the fuel pump connector vary from about 21 ohms empty to about 750 ohms when full, well within the specified range.
Something's off with the measurements or your post(s).
 

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Use a substituted load to test fuel gauge. Disconnect fuel pump connector and put a 20 to 100 ohm load across fuel gauge circuit. An incandescent test light should work as a substituted load. My test light has a resistance of 22 ohms. The fuel gauge should show full if circuit and gauge are working. If gauge is working then problem is in fuel sending unit. If gauge is not working then I think you should look for resistance in fuel gauge circuit.
 

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Discussion Starter · #9 ·
Here is what I have learned and tested so far. It appears that the 2008 Ody fuel gauge circuit consists of two components; the sending unit in the gas tank, and the instrument cluster. All the electronics necessary to convert the fuel sending unit resistance to a gauge reading appear to be in the instrument cluster. There are electronic circuits that convert the resistance to a digital signal that is sent to the stepper motor in the cluster that moves the needle on the fuel gauge. The instrument cluster self-test shows the stepper motors on all the instruments are working as they should, and the resistance test on the sending unit is within specification, and the float on the sending unit is free to move as it should, so the problem must be in the electronic circuit reading the fuel gauge. Shorts or opens in the wires would cause a diagnostic test code, so that is not the problem.
I have a second problem, that is the VSA Off switch does not disable traction control (stability control). I have replaced the switch with a new one, and the problem still exists. The car will not pass the new I.M 240 emission test mandated by the EPA effective January 2022 without this switch being able to disable the traction control. I do not understand what traction control being disabled has to do with clean air, but it seems Colorado Emission Testing will not perform the emission test without it working.
The VSA switch also connects to the instrument cluster, so it appears I need a replacement or repair of this cluster. For anyone interested, here is a partial schematic showing how these two systems are wired to the instrument cluster.
Rectangle Schematic Font Parallel Engineering
 

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If you have a TPMS light, VSA will not disable.
 
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Don't be too hasty to condemn cluster module. These two problems could be caused by a common fault other than cluster module or be independent faults. Anyway, pick one problem and troubleshoot it until you find the issue. I would work on fuel gauge first because it is much simpler than VSA system. You have eliminated shorts and opens in fuel gauge circuit, but not high resistance. High resistance will cause gauge to read low/empty. Use a substituted load like I described in previous post. This will quickly tell you if problem is in fuel gauge circuit (from cluster to fuel tank) or inside the tank.

I like the schematic in your last post, but it is missing ground for fuel gauge circuit. It is uses pin A21 on cluster for ground. I'm getting wiring information from AutoZone site, autozone.com/diy/repair-guides.
 

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a stepper motor moves the gas gauge?? Wow, that seems to be an overkill.
 
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