Engine Controls - Tests W/Codes - 6.5L Diesel.: Introduction

The 6.5L Diesel Electronic Control (DEC) system, electronically controls EGR system operation, Torque Converter Clutch (TCC) engagement, fuel control and fuel injection timing and is controlled by the Powertrain Control Module (PCM).

On diesel models with 4L60-E electronically-controlled transmission, transmission is controlled by the PCM. On "G" Series Van and "P" Series Commercial Van diesel models with 4L80-E electronically-controlled transmission, transmission is controlled by the Transmission Control Module (TCM). "P" Series Motorhome and all other diesel models with 4L80-E electronically-controlled transmission, transmission are controlled by the PCM. TCM only controls the electronic transmission and no other components.

The PCM/TCM monitors a number of transmission functions and uses the data to control shift solenoids, TCC, and pressure control solenoid to regulate upshift pattern, downshift pattern and line pressure (shift quality).

Most engine/transmission control problems are NOT computer related, but result from mechanical breakdowns, poor electrical connections, or damaged vacuum hoses. Before condemning the computer system, carefully perform visual and mechanical inspections covered in BASIC TESTING - 6.5L DIESEL article. Failure to perform these inspections can result in lost diagnostic time.

If no faults were found while performing visual and mechanical inspections in BASIC TESTING - 6.5L DIESEL article, go to DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no diagnostic trouble codes or only a non-running DTC 12 is present and driveability problems exist, proceed to TESTS W/O CODES - 6.5L DIESEL article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). If only intermittent codes are present, see INTERMITTENTS in TESTS W/O CODES - 6.5L DIESEL article.