I was getting ready to take my car in for service #2 this week. It is the second time I was ready to make the call. My mileage indicator has added miles to when the service needs to be completed. The first time it went down to 600 miles, and then jumped back to 1800 miles. The second time it went down to 900 miles and has gone back up to 1800 again. Is this normal or is there an electrical issue? The car has 24,000 miles and reads 1800 miles to the next service (service #2).