Fuel Gauge Problem

[goosefraba]

Fellows,

My 2012 SE's fuel gauge is not right. It started off by dropping to the low fuel light from 3/4 tank within a 20 minutes span... kept there for a couple days... then jumped to full after filling the tank... wandered a bit then popped up to full... stayed on full for 180 miles, then dropped to the low fuel light. Interestingly, the "range" display in miles computed accurately at one point with the Trip meter for a while, but jumped to back to wacky. I guess it will periodically take a tank reading in the computation? Last night, the gauge moved from fuel light and is now reading 1/4 tank steady (110 miles on tank, so the reading is still wrong).

I am out of warranty so would like to fix this myself. Do you recommend replacing the sender first? If replacing the sender, does the sender unit itself pop out of the pump/filter assembly, and does the wire pair connector pop out as well = meaning easy? I have a good idea what it takes to remove the assembly from the tank, but want to make sure there are no gotchas.

Are there fuses to try or would you recommend running diagnostics from the harness connector that plugs into the instrument cluster (which CTScott described which wires/pins to check ohms in a fuel gauge thread).

One problem is that I do not have a service manual and do formal instructions of how to remove the rear seat properly and how to get to the gauge cluster without possibly breaking stuff!! It seems to me that the service/repair manuals are not very available. Do you know a good source for a manual?
Thanks

[CTScott]

Originally Posted by goosefraba

Fellows,

My 2012 SE's fuel gauge is not right. It started off by dropping to the low fuel light from 3/4 tank within a 20 minutes span... kept there for a couple days... then jumped to full after filling the tank... wandered a bit then popped up to full... stayed on full for 180 miles, then dropped to the low fuel light. Interestingly, the "range" display in miles computed accurately at one point with the Trip meter for a while, but jumped to back to wacky. I guess it will periodically take a tank reading in the computation? Last night, the gauge moved from fuel light and is now reading 1/4 tank steady (110 miles on tank, so the reading is still wrong).

I am out of warranty so would like to fix this myself. Do you recommend replacing the sender first? If replacing the sender, does the sender unit itself pop out of the pump/filter assembly, and does the wire pair connector pop out as well = meaning easy? I have a good idea what it takes to remove the assembly from the tank, but want to make sure there are no gotchas.

Are there fuses to try or would you recommend running diagnostics from the harness connector that plugs into the instrument cluster (which CTScott described which wires/pins to check ohms in a fuel gauge thread).

One problem is that I do not have a service manual and do formal instructions of how to remove the rear seat properly and how to get to the gauge cluster without possibly breaking stuff!! It seems to me that the service/repair manuals are not very available. Do you know a good source for a manual?
Thanks

For your 3rd gen:

Once you get into the connector for the cluster, the fuel gauge comes in on the green wire in pin 16 of the 40 pin connector. There is a blue wire next to it in pin 17 and a brown wire on the opposite side of it in pin 14.

Looking at the connector from the back side where the wires come in and with the connector latch up:

20........1
40........21

If you unplug the connector from the cluster you can measure the resistance on the green wire (put one meter lead on it and the other on a chassis ground or any wire that is white with a black stripe).

The resistance with vary based on the fuel level and I believe that the 3rd gen uses the same sender as the 2nd gen, where the resistance goes from 13.5 ohms with a full tank to 414 ohms when empty.

If your fuel sender has a bad section, you will likely see a very high or open circuit reading when it drops from 3/4 to empty on you.

To remove the cluster you just pull the trim around it off with your finger tips. Once that is off just remove the mounting screws to pull the cluster out.

[goosefraba]

Thanks CTScott. The instrument panel was a really easy remove.. just pulled the trim gently and slowly, removed the 2 screws, then tilted it out.

I got a reading of 0 ohms with gauge stuck on the full mark before taking the reading. 117 miles on tank, so clearly the sender is not giving the resistance within the 13.5 to 414 ohms. 117 miles is roughly 3.4ish gallons from full. It makes sense that 0 ohms would peg the needle to full mark if less ohms is full and more ohms is empty.

I am going to take another reading after the gauge needle moves and sticks again. It would be nice to have an actual number correlation to the gauge needle being anywhere between the full and empty marks.... but based on this I think I am pretty certain the sender is bad.

[CTScott]

Originally Posted by goosefraba

Thanks CTScott. The instrument panel was a really easy remove.. just pulled the trim gently and slowly, removed the 2 screws, then tilted it out.

I got a reading of 0 ohms with gauge stuck on the full mark before taking the reading. 117 miles on tank, so clearly the sender is not giving the resistance within the 13.5 to 414 ohms. 117 miles is roughly 3.4ish gallons from full. It makes sense that 0 ohms would peg the needle to full mark if less ohms is full and more ohms is empty.

I am going to take another reading after the gauge needle moves and sticks again. It would be nice to have an actual number correlation to the gauge needle being anywhere between the full and empty marks.... but based on this I think I am pretty certain the sender is bad.

Lower resistance does equal more fuel, but its should not hit zero ohms, even when completely full.

[johannes]

Dear CTScott,

as I have found several posts concerning fuel pump problems, where you provided help: can you probably give me a hint how to get the pump out of a Yaris mk1 from 2000? My problem is shown in this thread:
http://www.yarisworld.com/forums/showthread.php?t=52565

Best regards, Johannes