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 Controls - Basic Testing: Introduction
The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.
The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions during which the problem reportedly occurred.
Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this 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 | ||||
| DLC Diagnosis | See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK | ||||
| No-Start Diagnosis | See NO START - ENGINE CRANKS OKAY | ||||
| No Scan Tool Data | See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK | ||||
| Fuel Pump Relay | See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article | ||||
| Fuel System Diagnosis | See BASIC FUEL SYSTEM CHECKS | ||||
| MAP Sensor | See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article | ||||
| Power Steering Pressure Switch | See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article | ||||
| Transmission Range Switch | See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article | ||||
| Injector Balance Test | See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article | ||||
| Injector Leak Test | See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article | ||||
| IAC Motor | See IDLE CONTROL SYSTEM in SYSTEM/COMPONENT TESTS article | ||||
| Canister Purge System | See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article | ||||
| Knock Sensor Check | See IGNITION SYSTEM in SYSTEM/COMPONENT TESTS article | ||||
| Air Injection System | See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article | ||||
| EGR System | See EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article | ||||
| 1-4 Upshift System (Manual Transmission) | See MISCELLANEOUS CONTROL SYSTEM/COMPONENT TESTS article | ||||
| Torque Converter Clutch | (1) See MISCELLANEOUS CONTROLS in SYSTEM/COMPONENT TESTS article | ||||
| A/C Compressor Clutch Control | (2) See MISCELLANEOUS CONTROLS in SYSTEM/COMPONENT TESTS article | ||||
| Electric Cooling Fan Control | (2) See MISCELLANEOUS CONTROLS in SYSTEM/COMPONENT TESTS article | ||||
| Engine Coolant Level Switch | See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article | ||||
| Oil Pressure Switch | See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article | ||||
| Oil Level Sensor | See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article | ||||
| PCM Controlled Warning Lights | See MISCELLANEOUS CONTROLS in SYSTEM/COMPONENT TESTS article | ||||
| Supercharger Boost Control | See AIR INDUCTION SYSTEMS in SYSTEM/COMPONENT TESTS article | ||||
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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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