4.3L, 5.0L, 5.7L (VIN R) & 7.4L

NOTE: Check for applicable Technical Service Bulletins (TSBs) before proceeding. Perform the following procedure only if a driveability complaint exists, or if you were sent here from another procedure or article. DO NOT turn ignition off during the following procedure or clear DTCs unless instructed to do so.

Connect scan tool. Turn ignition on, with engine off. Observe MIL. If MIL illuminates, go to next step. If MIL does not illuminate, go to MIL CIRCUIT CHECK .
Using scan tool, attempt to communicate with VCM. If scan tool displays VCM data, go to next step. If scan tool does not display VCM data, go to DLC DIAGNOSIS OR NO SCAN TOOL DATA .
Using scan tool, observe DTC status for MIL REQUEST, FAIL THIS IGN, LAST TEST FAIL and HISTORY. If any DTC is stored, save freeze frame and failure records information using scan tool CAPTURE INFO feature. Diagnose DTCs. See DIAGNOSTIC TESTS in appropriate TESTS W/CODES article. If DTCs are not present, go to next step.
Using scan tool, monitor SERIAL DATA CLASS II messages. If all other control modules are communicating with scan tool, go to next step. If all other control modules do not communicate with scan tool, go to DLC DIAGNOSIS OR NO SCAN TOOL DATA .
Attempt to start engine. If engine starts and continues to run, go to step 7. If engine does not start, or starts and then stalls, go to next step.
Using scan tool, check for any Passlock® DTCs. If DTCs are present, diagnose DTCs. See DIAGNOSTIC TESTS in appropriate TESTS W/CODES article. If no DTCs are present, go to NO START DIAGNOSIS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
Using scan tool, command MIL to turn off. If MIL turns off, go to next step. If MIL does not turn off, go to MIL CIRCUIT CHECK .
Compare scan tool engine data with typical control system data values. If values are within limits, see appropriate TROUBLE SHOOTING - NO CODES article. If values are not within limits, see appropriate SYSTEM & COMPONENT TESTING article.