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.
Engine Control System - System/Component Tests: Introduction
Before testing separate components or systems, perform procedures in the BASIC TESTING article. Since many computer-controlled and monitored components set a trouble code if they malfunction, also perform procedures in the TESTS W/CODES article.
The following table provides the location of commonly used diagnostic information.
| System Or Component | Diagnostic Information Location | ||
|---|---|---|---|
| Malfunction Indicator Light (MIL) | See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in BASIC TESTING article | ||
| DLC & MIL On Steady | See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in BASIC TESTING article | ||
| No Scan Tool Data | See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in BASIC TESTING article | ||
| No-Start Diagnosis | See appropriate NO-START - ENGINE CRANKS OKAY in BASIC TESTING article | ||
| Injector Circuit Diagnosis | See BASIC FUEL SYSTEM CHECKS in BASIC TESTING article | ||
| Fuel Pump Relay | See MODULES, MOTORS, RELAYS & SOLENOIDS | ||
| Fuel System Diagnosis | See appropriate BASIC FUEL SYSTEM CHECKS in BASIC TESTING article | ||
| Injector Balance Test | See FUEL SYSTEM | ||
| MAP Sensor | See ENGINE SENSORS & SWITCHES | ||
| Transmission Range Switch | See ENGINE SENSORS & SWITCHES | ||
| IAC Valve | See IDLE CONTROL SYSTEM under FUEL SYSTEM | ||
| Fuel Evaporation Control | See EMISSION SYSTEMS & SUB-SYSTEMS | ||
| Ignition Control Circuit | See IGNITION SYSTEM | ||
| Knock Sensor Check | See IGNITION SYSTEM | ||
| EGR System | See EMISSION SYSTEMS & SUB-SYSTEMS | ||
| Torque Converter Clutch | See MISCELLANEOUS PCM/VCM CONTROLS | ||
| Manual Transmission Shift Lights | See MISCELLANEOUS PCM/VCM CONTROLS | ||
| A/C Clutch Control | (1) See MISCELLANEOUS PCM/VCM CONTROLS | ||
| Electric Cooling Fan Control | (1) See MISCELLANEOUS PCM/VCM CONTROLS | ||
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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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