Code 10, Stoplight Switch On Constantly

1. Turn ignition off. Disconnect EBCM harness connector from EBCM. Turn ignition on. Measure voltage between EBCM harness connector terminal No. 8 and ground. See Fig 1 .
2. If reading is less than 10 volts, replace EBCM. If reading is 10-15 volts, replace or adjust stoplight switch or repair short to voltage in Green/White wire. See Fig 1 .

Fig 1: Stoplight Switch & Related Circuit ID

Courtesy of GENERAL MOTORS CORP.