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.

NOTE: Unless otherwise instructed in test procedures, perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance.

The following table provides location of commonly used diagnostic information. These former "A" and "C" charts are now written in text and inserted into appropriate location of engine performance workflow. To learn about engine performance workflow, see HOW TO USE THE ENGINE PERFORMANCE SECTION in this section.

GENERAL MOTORS A & C CHART REFERENCE

System Or Component

Diagnostic Information Location

A-1, Malfunction Indicator Light (MIL)

See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK

A-2, DLC & MIL On Steady

See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK

A-2, No Scan Tool Data

See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK

A-3, No-Start Diagnosis

See A-3, NO-START DIAGNOSIS

A-4, Injector Circuit Diagnosis

See appropriate BASIC FUEL SYSTEM CHECKS

A-5, Fuel Pump Relay

See RELAYS, SOLENOIDS, MOTORS & MODULES in SYSTEM/COMPONENT TESTS article

A-6, Fuel System Diagnosis

See appropriate BASIC FUEL SYSTEM CHECKS

A-7, Injector Balance Test

See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article

C-1, MAP Sensor

See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article

C-1, Power Steering Pressure Switch

See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article

C-1, Park/Neutral Switch

See ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article

C-2, IAC Motor

See IDLE CONTROL SYSTEM under FUEL SYSTEM in SYSTEM/COMPONENT TESTS article

C-3, Fuel Evaporation Control

See appropriate EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article

C-4, Ignition Control Circuit

See IGNITION SYSTEM in SYSTEM/COMPONENT TESTS article

C-5, ESC Ignition Check

See IGNITION SYSTEM in SYSTEM/COMPONENT TESTS article

C-7, EGR System

See appropriate EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article

C-8, Torque Converter Clutch

⁽¹⁾ See MISCELLANEOUS PCM/VCM CONTROLS in SYSTEM/COMPONENT TESTS article

C-8, Manual Transmission Shift Lights

⁽¹⁾ See MISCELLANEOUS PCM/VCM CONTROLS in SYSTEM/COMPONENT TESTS article

C-10, A/C Clutch Control

See MISCELLANEOUS PCM/VCM CONTROLS in SYSTEM/COMPONENT TESTS article

C-12, Electric Cooling Fan Control

⁽²⁾ See MISCELLANEOUS PCM/VCM CONTROLS in SYSTEM/COMPONENT TESTS article

⁽¹⁾	Covered in entirety in appropriate AUTO TRANS DIAGNOSIS article.

⁽²⁾	Covered in entirety in A/C-HEATER SYSTEM article in the AIR CONDITIONING & HEAT section.

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.

Safety Warning

Engine Controls - Basic Engine Testing - P Series (Gasoline): Introduction

Use the Manual With the Right Hardware

When to See a Mechanic

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