O2 Sensor Failure CEL & TSC light on simultaneously. With OBDII systems it's possible that if you have a CEL indicating a bad O2 sensor you can also get a TSC light but with no codes. The reason for this is that the O2 heaters are powered by #5 fuse in the dashboard fuse panel, which also provides power to the TSC, and a bad heater may be causing a voltage drop affecting the TSC system. If this happens, the way to test it is to measure the voltage across the fuse 5 contacts via the tiny holes located at the top of each fuse. If the voltage measures less than 8v it will cause a TCS light to come on. A 96 that I recently worked, which had this problem, measured 6v across the fuse. Once the O2 sensors were replaced the TCS light was no longer illuminated.
