GM
Type:
    Powertrain - Manufacturer Controlled DTC - Manufacturer Controlled
Description:
    Internal Mode Switch - Invalid Range (4T65-E Transmission)
Cause:
    DTC P0502 and P0503 not set, DTC P1826 has passed this key cycle, system voltage from 9-18v, engine speed at least 500 rpm for 5 seconds, Fuel Shutoff inactive, engine torque more than 20 ft-Ibs, then the PCM detected that the Internal Mode Switch 'C' signal was in a high state while the gear ratio indicated 1st, 2nd or 3rd gear, condition met for 0.5 seconds.