Q: My digital fuel mileage read out and is going up and down erratically

asked by on

Two days ago I noticed my fuel mileage was at 17.2 mpg. I normally get between 16.5 and 17.5 mpg because I drive on the highway a lot to and from work. As I was driving to work two days ago the reading began to jump drastically so that by the time I parked at work the mileage read 22.6 mpg. I was only on the road for 20 minutes so I know that's wrong. But then the next day on my way to work it began dropping as drastically. By the time I got to work it read 13.7 mpg. I tried resetting it through the steering wheel controls but it didn't make a difference. The truck runs fine and I haven't noticed an increase in fuel consumption. What could be the issue?

My car has 60500 miles.
My car has an automatic transmission.

Most "fuel economy estimators" utilize the length of time the fuel injectors are open (we’re talking milliseconds here) during each revolution of the engine while driving. As a result, small periods of acceleration or other load factors will have temporary injection length periods far greater than a longer term average.

So you get wide swings on fuel mileage as you observe. On some models, you have the option for averaging fuel mileage calculated on a trip, or have it average "instantaneously". The behavior you describe sounds more like it is using the very short term, instantaneous mileage calculation. Time to get the owners manual out and reset for a longer term statistic if that is more meaningful to you. If you would like to have this scoped out in person, a qualified professional from YourMechanic can come to your car’s location to inspect the mileage problem and follow through with repairs.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. My digital fuel mileage read out and is going up and down erratically

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: CV Axle failure.

Hello there, without knowing which parts the dealer determined to be faulty I can only offer general advice for your 2011 Dodge Ram 1500. The CV shaft, CV boots, and axle assembles are common repair items, any one of these...

Q: honda accord will not start

Hello, thank you for writing in. In these situations always start with the basics. First, when turning the vehicle over to try and start it, a slow cranking speed may indicate you have a weak starter or battery. The starter...

Q: I have a 2005 Chrysler 300c hemi. Yesterday I noticed the car was making a sound like driving over rumble strips between 40 and 60 mph.

Check the front wheel bearings on your vehicle. A failing wheel bearing that is dry of grease will cause the rumble sound. Jack the vehicle up and spin the front wheels and listen for the noise. If the noise is...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...