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 help prevent overlooking simple problems. This is also where to begin diagnosis for no-start condition.
The first step in diagnosing any driveability problem is verifying the customer's complaint by test driving vehicle under the conditions in 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.
| System Or Component | Diagnostic Information Location | ||||
|---|---|---|---|---|---|
| DIAGNOSTIC CIRCUIT CHECK | See appropriate DIAGNOSTIC CIRCUIT CHECK | ||||
| A-1 & A-2, Malfunction Indicator Light (MIL) | See appropriate DIAGNOSTIC CIRCUIT CHECK or appropriate TESTS W/CODES article. | ||||
| A-3, No-Start | See A-3, NO-START DIAGNOSIS | ||||
| A-5, Fuel Pump Relay | See RELAYS, SOLENOIDS, MOTORS & MODULES in I - SYS/COMP TESTS article in this section | ||||
| A-6 & A-7, Fuel System Diagnosis | See appropriate BASIC FUEL SYSTEM CHECKS | ||||
| C-1, MAP Sensor | See ENGINE SENSORS & SWITCHES in I - SYS/COMP TESTS article in this section | ||||
| C-1, Power Steering Pressure Switch | See ENGINE SENSORS & SWITCHES in I - SYS/COMP TESTS article in this section | ||||
| C-1, Park/Neutral Switch | See ENGINE SENSORS & SWITCHES in I - SYS/COMP TESTS article in this section | ||||
| C-2, Injector Balance Test (4.3L) | See FUEL CONTROL under FUEL SYSTEM (GAS) in I - SYS/COMP TESTS article in this section | ||||
| C-2, IAC Motor | See IDLE CONTROL SYSTEM under FUEL SYSTEM (GAS) in I - SYS/COMP TESTS article in this section | ||||
| C-3, Canister Purge System | See appropriate EMISSION SYSTEMS & SUB-SYSTEMS in I - SYS/COMP TESTS article in this section. | ||||
| C-4, EST Ignition Check | See C-4, BASIC IGNITION SYSTEM CHECKS (GASOLINE) | ||||
| C-5, ESC Ignition Check | See IGNITION SYSTEM in I - SYS/COMP TESTS article in this section | ||||
| C-6, Air Injection System | See appropriate EMISSION SYSTEMS & SUB-SYSTEMS in I - SYS/COMP TESTS article in this section | ||||
| C-7, EGR System | See appropriate EMISSION SYSTEMS & SUB-SYSTEMS in I - SYS/COMP TESTS article in this section | ||||
| C-8, Torque Converter Clutch | (1) See MISCELLANEOUS ECM CONTROLS in I - SYS/COMP TESTS article in this section | ||||
| C-8, Manual Transmission Shift Lights | (1) See MISCELLANEOUS ECM CONTROLS in I - SYS/COMP TESTS article in this section | ||||
| C-10, A/C Clutch Control | See MISCELLANEOUS ECM CONTROLS in I - SYS/COMP TESTS article in this section | ||||
| C-12, Electric Cooling Fan Control | (2) See MISCELLANEOUS ECM CONTROLS in I - SYS/COMP TESTS article in this section | ||||
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NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.