Transmission Diagnosis - With Codes: Operation: Diagnostics

While the ignition is on, the auto gear box control unit diagnoses the system for faults. The extent of the diagnostic capability at any particular time depends on the prevailing operating conditions, e.g. it is not possible to check torque converter lock-up while the vehicle is stationary, or to check for a short circuit to ground if the circuit concerned is already at a low potential. If a fault is detected, the auto gear box control unit immediately stores a fault code and the values of 3 operating parameters associated with the fault. Depending on the fault, there are 4 possible effects:

• The fault has little effect on automatic transmission operation or vehicle emissions (will not increase emissions by 15 percent). The driver will probably not notice any change and the warning lamps remain extinguished.
• All gears are available but kickdown does not function. GEARBOX FAULT will be displayed on the instrument cluster message center. The MIL remains extinguished.
• Limp home mode is selected and vehicle performance is greatly reduced. GEARBOX FAULT will be displayed on the instrument cluster message center. If the fault is detected on a second consecutive drive cycle, the MIL illuminates.