Section 13 (Engine Controls - Tests W/Codes - Electronic Transmission): Introduction

On gasoline vehicles with 4L60-E or 4L80-E transmission, transmission is controlled by the Powertrain Control Module (PCM). PCM controls other vehicle functions as well as the transmission. On diesel vehicles with 4L80-E transmission, electronic transmission is controlled by the Transmission Control Module (TCM). TCM controls no other components. The PCM/TCM monitors a number of engine/vehicle functions and uses the data to control shift solenoid "A", shift solenoid "B", TCC, and the pressure control solenoid to regulate upshift pattern, downshift pattern and line pressure (shift quality).

Most engine/transmission control problems result from mechanical failures, poor electrical connections or damaged vacuum hoses. Before condemning the computer system, perform checks and inspections, including the diagnostic circuit check or diagnostic system check, covered in BASIC TESTING - GASOLINE article in this section. Failure to do so may result in lost diagnostic time. On diesel vehicles, diagnostic system check is covered in TESTS W/CODES - 6.5L DIESEL article in this section.

If no faults were found while performing checks and inspections in BASIC TESTING - GASOLINE article in this section, go to DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no fault codes or only a non-running Code 12 is present and driveability problems exist, proceed to TESTS W/O CODES - GASOLINE article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in TESTS W/O CODES - GASOLINE article in this section.