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Old 04-27-2013, 08:27 PM
Chuck W.'s Avatar
Chuck W. Chuck W. is offline
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Location: Agoura Hills (LA) CA
Join Date: Apr 2007
Posts: 1,180
Mein Auto: 12 BMW 535I MS Alpine Wht
Originally Posted by jjsC6 View Post
I see some folks who question the car's calculated mpg. I seriously doubt if it is off by much at all, and it's likely to be as accurate as using the calculator method. If you calculate by "hand" are you sure your filling up the tank to the same level every time? Have you checked to see if the odometer is accurate?

The reality is that with the current electronics and information supplied on-line they very accurately measure how much fuel is being electronically metered to the engine. I'm sure there could be some variance, but it's very unlikely they are off by more than 1-2%. While I don't use a calculator, I frequently run the numbers in my head, and I've always done it. They aren't off by much.
I kept track for several tanks and the car was off an average of 4% - read high. I used the below method to reset the car with great success.

Mine read 4.0 high. I found the below procedure worked to reset the gas MPG computer.

1. Hold down the odometer reset button and turn the ignition on by pushing start/stop button.

2. Release the odometer reset button, and you should see a menu of 4 items on the dashboard. From here on, use the odo-reset button to advance to the next entry through a short press, and to select through a long press.

3. Choose the one that says Unlock through the above, which will take you to a passkey screen. Your passkey is the sum of the last 5 digits of your VIN. Increment the two-digit number until you get to it, and with the long press of the odo button, select it.

4.Then scroll down to correction factor and modify it from 1000 to whatever you require.

My car claimed more mpg than it was actually delivering by about 4.0%. I changed the 1000 to 1040 and it now seems about right.

If your trip computer reads higher than true figures worked out, make the correction over 1,000. If your trip under reads, make the correction number under 1,000.
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