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I personally think my average speed is low. I drive mostly highway. 43 mph is child's play.
I reset everything in the DIC at each fill up. That way I'll know my readouts are current and not being averaged off of old mileage stuff.
FYI. My avg speed is usually around the 29-32 range when I fill up. Mileage is always around 27-27.5 (by the DIC and pencil/paper )
Possibly the speed sensor has crapped out or the wiring knocked loose , it lives on the passenger side of the transmission facing towards the passenger toe board
It’s that little sensor just one bolt holds it into place.
My avg. speed usually says 35... My actual speed 90% of the time is above 55 on rural back roads. Go figure.
And you NEVER idle? 0 MPH in a average affects the calculations a lot.
I think we figured her odometer problem out a while ago. The instrument panel was replaced by an amateur that never got it programmed. There will be legal problems when the car is resold.
The calculations are based on cubic meters of AIR induced through the MAF. The tank level is determined by the air pressure in the tank assuming that the engine is OFF when the tank is filled.
420 miles on a 10.5 gallon tank of gas is pretty exceptional! Do you really expect 42 MPG?
I was covering several post in one. The only part aimed at you was the idling.
The OP stated 420 miles was usual after a fill up. And now, an equally unbelievable 365 or 375.
Pretty sure that all years of the HHR had a 16.2 gal fuel tank. I know I've seen my readout say 434 miles miles left after a fill up. (27 x 16.2 = 437)
