Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Self-Diagnostic System: Description: Notes
Powertrain Control Module (PCM) is equipped with a self-diagnostic system, which detects system Diagnostic Trouble Codes (DTCs) or abnormalities. When a malfunction occurs, PCM will store a DTC. Malfunctions are recorded as history/intermittent failures or as current failures. Current DTCs indicate PCM has detected a fault which is currently present. A history DTC indicates that PCM has previously detected a malfunction that is not currently present as it is either an intermittent condition or the system is not being currently operated.
Instrument Panel Cluster (IPC) can be used to retrieve and clear DTCs. A scan tool can be used to retrieve and clear DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES . The scan tool also has several features that can be used to help locate an intermittent condition. When scan tool is used for system tests, it will display values actually seen or commanded by various systems (i.e., BCM, PCM). This will usually include the following types of information:
- Analog Data Input
Displays analog input seen by system. - Inputs/Outputs
Displays digital values as seen by system, and provides indication of whether input or output has cycled. - Special Functions (Output Controls)
Allows for outputs of system to be set at a desired value (ON or OFF). This will only indicate if IPC is sending the appropriate commands, not what action was actually taken. - Clear Codes
Will erase DTCs for system currently selected (if problem still exists in system, DTC may immediately reset).
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.