My sons 92 Camry, approx 250,000 miles, 4 cylinder, auto trans, reports his speedometer is running slower than his actual speed (compared to a GPS device and the other traffic around him). No other problems with the car electrically and the trans shifts normally. The overdrive button is "on" and there is no flashing of the OD indicator indicating a problem so there are no codes. My thinking is that if Speed Sensor #1 or #2 were at fault they would set a code and flash the OD indicator light and they would be the type of unit that would either work or not. I'm thinking the speedometer gauge is the problem. Anybody have any other thoughts on the subject? In advance, thanks to all.

If the speedo is consistently reading low, then it could be a poor contact in a wiring connection or a failing instrument cluster. If it abruptly jumps between normal and low, then it could be the speed sensor.

One other possibility is if your son has installed larger tires/wheels than the OEM type. This would cause them to rotate slower to cover the same distance, resulting in a lower speedometer reading.

No wheel and tire changes have taken place and the speedometer "action" is smooth, just overall low in speed.

If the vehicle has no trouble codes showing as you describe, shifts normally, and fuel economy has not suffered, then it may well be the instrument cluster. It may be something as simple as dirty, oxidized, or corroded contacts going to the cluster.

You can refer to the stickies at the top of the Camry forum to confirm his car is shifting at the proper speeds...download the AX1.PDF for the 4-cylinder transmission.

How much different is the GPS from the speedometer reading? Readings of 2-3 MPH difference at highway speeds can be considered normal in my opinion. My 94 Camry is dead on with my GPS but my 07 Camry reads 2 MPH faster than my GPS.

Mike