HELP! I just bought a 2008 G37s Coupe. 6 spd manual. I drove it well over 400 miles home on the interstate, but the odometer only registered about 100 miles of that trip. The previous owner rarely drove the car and it was in storage for a couple of years during Covid. He was not aware of any issues and even offered to help pay for repairs if I could figure out what needed to be done. I found a previous thread that mentions this issue but no resolution was ever given. It was an old thread and no one responded, so I am posting a new one.

Here's what I know so far:
- Speedometer reading is accurate (tested by driving alongside a friend's vehicle at a known speed)
- ECU reports the exact same number as the digital odometer on the dash. My mechanic interrogated the ECU with a professional reader capable of reading the mileage. HOWEVER, is the odometer telling the ECU the mileage, or is the ECU telling the Odometer what to display?
- Factory wheels and tires. It's not a minor tire diameter discrepancy, it's 1 mile recorded for every 4-5 miles driven.
- The trip meter matches the odometer reading. In other words, if the odometer counts up 10 miles, so does the trip meter. In such a scenario, I would have had to drive the car 40-50 miles to get the odometer to count up 10.
- I disconnected the battery for a couple of hours, no change
- I did an ECU reset (turn on ignition, do the little dance with the throttle pedal, waiting seconds, pushing a few times, push and hold, etc. Watch the flashing lights. The standard reset procedure). No change.

Questions:
- Where is the Odometer calculation done...by the ECU?... the Odometer circuit board on the cluster?... or somewhere else (the A/C amplifier board?)
- Where is the most likely place to start? Cluster repair $200+? Used A/C amplifier module $100 ebay? ECU repair/swap $300+? ABS controller?
- Can I rule out the wheel sensors because my speedometer is accurate?

The diagram shows the electrical chain. Because my speedometer is accurate, I'm going to assume that my speed sensors are fine. Is that a fair assumption?