TCS Diagnostics
This is the diagnostic to check the steering wheel position sensor on the Traction Control System. Please use this as a reference and buy the manual if you are going to be servicing the real thing.
TCS Problem Code Indication

  1. Stop the engine.

  2. Turn the ignition switch on and confirm that the TCS indicator light comes on.

  3. Turn the ignition switch off.

  4. Short the Service Check Connector.

  5. Turn the ignition switch on, but do not start the engine.

  6. Record the blinking frequency of the TCS indicator light.

The blinking frequency indicates the problem code. Long blinks indicate the main code; short blinks indicate the sub-code. Refer to the Troubleshooting Guide (page 19-84) for repair information.
Typical codes are 1-2 for TCS control unit, 2-1 for the steering wheel angle sensor, and 4-1, 4-2, 4-4, and 4-8 for the right front, left front, right rear, and left rear wheel sensors.
Now suppose you got the code for the steering wheel angle sensor. The TCS control unit performs the self-diagnosis for the steering angle sensor when the average speed of the front two wheels exceeds 16 km/hr. The TCS indicator light comes on if the yaw rate is generated and the steering angle signal that corresponds to this yaw rate is not input when the steering wheel is turned while there is no input from the STOP (brake light signal) and PARK (Parking brake signal).
Then there is a troubleshooting flow chart that starts something like this:

  1. Start the engine.

  2. Push the TCS switch 3 times within three seconds.

  3. Turn the steering wheel slowly from left to right more than 1.5 turns.

  4. Push the TCS switch 2 times within 3 seconds.

  5. Return the steering wheel to the left side slowly, check the number of times the TCS indicator light flashes after the wheel has moved approximately one turn.

Does the light flash five times? If the answer is yes, then you have tire size/pressure problems. A no answer indicates further testing is required.