Toyota Cluster Display MPG vs OBDII Logger MPG

I have spent the last 2 months running in circles trying to map the Fuel Consumption signal from the Engine ECU to the instrument cluster display. After lots of testing, some conversion errors ect. I think I have finally cracked it.

The big question is how accurate do you guys think the Toyota display is for reporting Instant and Avg. MPG? You guys think it’s spot on? Over reporting? Under reporting?

I have done a few highway runs logging my data and get about 16Mpg Avg on my 5.7 at highway speed 70Mph. I calculate this using a summation of total fuel burned vs distance travelled.

I logged the data at the same time with an OBDII diagnostic software. It determines instant and avg Mpg based on the MAF signal. It also showed about 16 Mpg Avg.

However my factory Toyota display was showing more like 14 Mpg Avg. I had reset it prior to logging to erase all old data.

Any of you guys using Torque Pro or OBD fusion or similar apps have a comparison of what they say for MPG vs what your Toyota display says? I have a slight feeling Toyota might be adding a small “safety factor” to the data inside the cluster then displaying it. They seem to like being conservative with low fuel light ect.

I should note I have started logging Fuel fill ups vs Mileage as an additional source. Next time I fill up I will have a good Avg number based on hand calculations.

Just for fun I am going to continue to monitor 4 different sources, my microcontroller code, OBDII software, Toyota Display, and hand calculations at fill ups. Am interested to see how much they vary from each other. Currently my code and OBDII line up pretty close, Toyota is under and I don’t have a hand calculation yet.I will post some data and graphs in the future as I log more city and highway trips.