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: Notes
For PCM (ECM) REPLACEMENT CHECK see BASIC TESTING article in this Section
Self-diagnostic system consists of 4 components. These components are Powertrain Control Module (PCM), Instrument Panel Cluster (IPC) options, A/C Programmer (ACP) options and Supplemental Inflatable Restraint (SIR) system.
In addition to monitoring a particular set of sensors and switches, PCM is a major part of self-diagnostic system, maintaining continuous communication with each system component. Should a component exceed pre-programmed limits, PCM will recognize a malfunction and may act to control malfunctioning component. To control a particular component, PCM rapidly switches an internal circuit between zero and 5 volts, converting programmed control information into a series of pulses that represent coded serial data messages. These messages are transmitted to malfunctioning component, which interprets information and responds accordingly.
As a result, an alphanumeric code, known as a trouble code, is often set in PCM memory. This trouble code identifies malfunctioning component and can be accessed by a service technician as an aid to diagnostic procedures. All trouble codes are displayed on Driver Information Center (DIC) panel.
In addition to monitoring self-diagnostic system and displaying trouble codes, PCM can be programmed by service technician to perform specific diagnostic tests on individual components and systems. Results of these tests are displayed on DIC. This article covers accessing PCM trouble codes and programming self-diagnostic system to perform specific diagnostic tests on system components.
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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.
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