Fuel gauge off?

I recently d/c’d my battery to clean the terminals. I know this throws the computer off when it comes to tank range bc the computer has to relearn everything, however, I recently filled my tank to full and reset my trip stick after filling. As you can see I’m approaching half a tank and my trip stick is only showing a meager 115 miles, which means I’ll have only gotten roughly 250 miles out of this full tank by the time I’m empty. (Yes I know we have 6-8 gal reserve when the light comes on) but I’ve been consistently getting 350-380 miles out of a full tank (from full to until E-light comes on)
As you can see my range is showing 324 miles (obviously this is wrong if I’m almost at half a tank, but this is proof of the computer having to “re-learn.”)

It’s as if my fuel gauge is off…

FWIW I did just move up to 35” tires, but I shouldn’t have lost 100 miles on a tank. (Computer still shows 10-12mpg)

Does the computer also have to “re-learn” the fuel gauge?

Would the speedo being off by ~5mph now with larger tires ALSO throw the odo or fuel gauge off?


Thoughts?

 

I’d give it a few more fill ups. Mine does the same thing when I disconnect the battery. Normally it shows 410 DTE but goes up to 600+ when I disconnect the battery. It takes it a few tanks to relearn. 115 for a half tank would be low, even for 35s.

Fill it up now and see how much it takes. I think mine takes about 15 gallons at half a tank. If it’s much less, then your gauge might be off.

 

Thanks Tim, I’ll update after a few more fill ups.

 

I get 16 mpg with 35.1 tires. It takes about 300 to 500 miles on my truck for it to relearn after battery is disconnected.

 

Yeah I’m clear the tank range or distance to empty takes some driving to normalize, my concern is the fuel gauge being “off”
Have you ever felt like your fuel gauge/needle was off after disconnecting battery?

 

No

 

Also No.

Give it a few more fill up cycles and then assess.

 

Will do, thanks.

 

yeah whatever % your speedometer being off say 10% your odometer will also be off by same amount since it reads distance traveled based on stock height wheels and basically counts rotations. So larger wheels make it go further than it thinks it is

 

Fuek gauge operates ona direct line to the fuel tank and sender. The sender is a variable resistor that increase the resistance on the direct line as the fuel level drops. If can only be off if your float is stuck or broken, not from disconnecting the battery.

Speedometer, Odometer, Trip will all be off as they are calibrated to the wheel speed sensors and stocks tire size. The ABS/Stability control ecu monitors the pulses from the wheel speed sensors and calculates a speed, distance moved and sends these values to the cluster. Fastest way to check this is with a free speed/distance app on your phone. It will use GPS to show your actual speed and distance moved.

Avg. MPG and Range calculations are all done inside the cluster. The engine ecu sends it a signal of fuel burned at a certain rate, it then does the math to get the MPG. Most people report it takes some driving to get all this values to balance back out after resetting them.

 

thank you. I’ll report back after some more fill ups.

 

So in essence I would be accruing miles 10% slower?

 

yeah

 

Its more like 8% with a 35 inch tire.

Think of it in amount of wheel rotations per mile, the tall 35 inch tire has to do less rotations to travel a mile compared to the stock tire which the odometer is programmed it. When the odometer increment's 1 mile, your bigger tires have already traveled a mile and then some. If you go on a trip and your trip odometer says you travel 100 miles in reality you have traveled 108 miles, the odometer is just lagging behind because it thinks your tires are smaller.

How far is your speedo off at highway speed? Say 70Mph on the gauge mean you are really going like 76, check with one of those GPS Speed apps?

 

damn bro did you get the 2016 hybrid V8.

 

Makes perfect sense, thanks man. Yeah my speedo is off by 5 mph at 80 mph on the highway. Tryin to decide if i should do the hypertech recalibration?

 

Hypertech and Rough Country both only sell inline programmers I believe. These plug inline between your Engine ECU and Cluster, they read the incorrect factory speed signal coming in, apply the correction factor and send the new signal to the cluster. I know they correct the Speed signal but I am not sure if it reads and corrects the distance signal also, I would assume so.

I have heard rumors some Toyota Dealers can reprogram the speedo. I believe they have a way to get into the ECU and reset the number of Pulses from the wheelspeed sensors to equal a mile. This is the proper way to fix it but harder to do. I assume Toyota is setting this value for the factory as some trucks comes with factory 20 inch wheels while others have 18 inch wheels. Each would have a different amount of pulses from the wheel speed sensor per mile.

I would love to find a dealer who does this so I can see what software they are using ect. I believe it requires a Toyota ECU flasher, maybe can be done with something like HP Tuners.

 

that would be really awesome and convenient if the Toyota dealership could reprogram for us.

 

Thanks for all the responses. After refilling the tank once after this post was made, I am now inclined to believe the fuel gauge also has to “re-learn” just like the tank range does. I am attaching 3 pics. One is the original picture showing a measley 115 miles at nearly half a tank. Second picture is showing the needle at nearly the same position, however, this time I attained 159 miles. In between pics I refilled the tank from
Half back to full. 3rd pic is showing I’ve attained 175 miles at a half tank, which will hopefully put me at, or close to 350 miles on a full tank (trip stick at 350 miles when gas light comes on and range is 0). Also to be clear, the driving I did between fill ups (the 115 mile trip stick and 159 mile trip stick) I drove with the same driving behavior and same city driving. Also, as you can see the tank range is still re-learning. The stock days of 450 miles+ on a tank was nice, but since then I’ve upgraded my truck substantially to include 35x12.50 tires, steel bumper, steel skids, sliders, camper shell (all the heavy stuff lol).