Diagnostic Procedure

NOTE: Do not perform this diagnostic if there is not a driveability concern, unless another procedure directs you to this diagnostic. Before you proceed with diagnosis, search for applicable service bulletins. Unless a diagnostic procedure instructs you, do NOT clear the DTCs. If there is a condition with the starting system, see appropriate STARTERS article in ELECTRICAL. Ensure the battery has a full charge. Ensure the battery cables are clean and tight. Ensure the PCM grounds are clean, tight, and in the correct location.

Install a scan tool. Does the scan tool turn ON? If yes, go to next step. If no, see SCAN TOOL DOES NOT POWER UP in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
Turn ON the ignition, with the engine OFF. Attempt to establish communication with the listed control modules. If you are using a Tech 2®, obtain the information using the Class 2 Message Monitor feature:
- PCM.
- Body Control Module (BCM).
- Instrument Panel (IP) cluster.
- Electronic Brake Control Module (EBCM).
- Driver Information Center (DIC).
- Heating, Ventilation, and Air Conditioning (HVAC).
Does the scan tool communicate with all the listed control modules? If yes, go to next step. If no, see SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.

NOTE: The engine may start during this step. Turn engine OFF as soon as CRANK POWER MODE is observed.

Fig 1: Identifying Ignition Switch Inputs

Courtesy of GENERAL MOTORS CORP.

Access CLASS 2 POWER MODE in DIAGNOSTIC CIRCUIT CHECK on scan tool. Rotate ignition switch through all positions while observing IGNITION SWITCH POWER MODE parameter. Actual ignition switch position should match IGNITION SWITCH POWER MODE parameter on scan tool. See Fig 1. Do all ignition switch positions match all IGNITION SWITCH POWER MODE parameters on scan tool? If yes, go to next step. If no, see POWER MODE MISMATCH .
Attempt to start the engine. Does the engine start and idle? If yes, go to next step. If no, see NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - FLEX FUEL & GASOLINE article.
Select the DTC display function for the following control modules: PCM, BCM, IP Cluster, EBCM, DIC and HVAC. Does the scan tool display any DTCs? If yes, go to next step. If no, go to step 10.
Using a scan tool, select CAPTURED INFO in order to store the powertrain DTC information. When complete, go to next step.
Does the scan tool display DTCs which begin with a "U"? If yes, see appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT for diagnosis. If no, go to next step.
Does the scan tool display DTC P0601, P0602, P0604 or P0606? If yes, see DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681, P1683 & P2610: PCM MEMORY under DIAGNOSTIC TESTS. If no, go to next step.
Does the scan tool display DTC P0562, P0563, P1637 or P1638? If yes, see appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS. If no, see DIAGNOSTIC TROUBLE CODE DEFINITIONS .
Is the customer's concern with the automatic transmission? If yes, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. If no, go to next step.
Is the customer's concern with Inspection/Maintenance (I/M) testing? If yes, see INSPECTION/MAINTENANCE SYSTEM CHECK under DRIVE CYCLES.
Review the following symptoms. Hard start, surges/chuggles, lack of power, sluggishness, sponginess, detonation/spark knock, hesitation, sag, stumble, cuts out, misses, poor fuel economy, poor fuel fill quality, rough, unstable, or incorrect idle and stalling, dieseling, run-on and backfire. Proceed to SYMPTOMS in TROUBLE SHOOTING - NO CODES - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - FLEX FUEL & GASOLINE article. Did you find and correct the condition? If yes, system is okay. If no, see INTERMITTENT CONDITIONS .