OBC mpg way off?

[Semblance]

Not like it's a big deal, but my OBC tells me I'm getting about 15 mpg, but when I count the miles and gas myself I get 19+

how does the OBC do this calc? My gas gauge isn't reading the actual amount, I think I have a bad sender and it always reads low. But I'd be somewhat surprised if that's where the obc gets its info...

Anyway, just curious. Thanks!

[cabriodster87]

mpg,
how does the OBC do this calc?

Injector pulse count, and vehicle speed, so there are many variables.

Tire circumference, gear size, injector condition, etc

[Semblance]

She's bone stock, so sounds like it may be the injectors. I'll have to check if the odo and speedo are reporting correctly.