Diagnosis & Testing: Introduction

NOTE: Before testing transmission, ensure fluid level is correct and throttle and shift cables are properly adjusted. Ensure engine starts with shift lever in "P" (Park) and "N" (Neutral) to ensure proper adjustment of park/neutral position switch. Transmission must first be tested by checking for stored Diagnostic Trouble Codes (DTC). See RETRIEVING DIAGNOSTIC TROUBLE CODES .

ECM monitors engine and transmission operation and contains a self-diagnostic system which stores (DTC). A Malfunction Indicator Light (MIL), located on instrument panel, will illuminate if a system or component fails and sets a DTC. See Figure.

MIL illuminates with ignition switch in ON position, engine off (KOEO). Once engine is started, MIL should go out. If MIL remains illuminated, ECM has detected a malfunction or abnormality in system. If MIL does not illuminate, inspect circuit and light. See WIRING DIAGRAMS .

If malfunction does not reoccur in 3 trips, MIL goes off, but DTC remains recorded in ECM memory. DTCs may only be retrieved using scan tool connected to 16-pin Data Link Connector (DLC3), located at lower left corner of instrument panel. See Figure and Figure . Scan tool also provides freeze-frame data and can be used to clear DTCs.

ECM records engine operating condition (fuel system, calculated load, coolant temperature, fuel trim (mixture), engine speed, vehicle speed, etc.) with first DTC ONLY. Information is ONLY for 1st recorded DTC, even if more than one code has been recorded. Freeze-frame data is only updated when all DTCs have been cleared, or a misfire or fuel-trim malfunction has occurred.