MODEL IDENTIFICATION
| Series (1) | Model |
|---|---|
| "C" | Sierra, Suburban, Tahoe & Yukon |
| "G" | Van |
| "K" | 4WD Pickup, Sierra, Suburban, Tahoe & Yukon |
| "P" | Commercial Van/Motorhome |
| (1) Vehicle series is fifth character of VIN. | |
| (1) | Vehicle series is fifth character of VIN. |
MODEL IDENTIFICATION
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.
Note. Unless otherwise instructed in test procedures, perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance.
Note. 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.
| System Or Component | Diagnostic Information Location |
|---|---|
| DIAGNOSTIC CIRCUIT CHECK | See appropriate DIAGNOSTIC CIRCUIT CHECK |
| A-1 & A-2, MIL | See appropriate DIAGNOSTIC CIRCUIT CHECK |
| A-3, No-Start | See A-3, NO-START DIAGNOSIS |
| A-5, Fuel Pump Relay | See RELAYS, SOLENOIDS, MOTORS & MODULES (1) |
| A-6 & A-7, Fuel System Diagnosis | See appropriate BASIC FUEL SYSTEM CHECKS |
| C-1, MAP Sensor | See ENGINE SENSORS & SWITCHES (1) |
| C-1, Power Steering Pressure Switch | See ENGINE SENSORS & SWITCHES (1) |
| C-1, Park/Neutral Switch | See ENGINE SENSORS & SWITCHES (1) |
| C-2, IAC Motor | See IDLE CONTROL SYSTEM under FUEL SYSTEM (1) |
| C-3, Canister Purge System | See appropriate EMISSION SYSTEMS & SUB-SYSTEMS (1) |
| C-4, EST Ignition Check | See C-4, BASIC IGNITION SYSTEM CHECKS |
| C-5, ESC Ignition Check | See IGNITION SYSTEM (1) |
| C-6, Air Injection System | See appropriate EMISSION SYSTEMS & SUB-SYSTEMS (1) |
| C-7, EGR System | See appropriate EMISSION SYSTEMS & SUB-SYSTEMS (1) |
| C-8, Torque Converter Clutch | See MISCELLANEOUS ECM CONTROLS (1) |
| C-8, Manual Transmission Shift Lights | See MISCELLANEOUS ECM CONTROLS (1) |
| C-10, A/C Clutch Control | See MISCELLANEOUS ECM CONTROLS (1) |
| C-12, Electric Cooling Fan Control | See MISCELLANEOUS ECM CONTROLS (1) |
| (1) See SYSTEM/COMPONENT TESTS - 6.5L DIESEL article in the ENGINE PERFORMANCE section. | |
| (1) | See SYSTEM/COMPONENT TESTS - 6.5L DIESEL article in the ENGINE PERFORMANCE section. |
"A" & "C" CHART REFERENCE
VISUAL INSPECTION
Visually inspect all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. If necessary, see the appropriate VACUUM DIAGRAMS - 6.5L DIESEL article to verify routing and connections. Inspect air induction system for possible vacuum leaks.
Compression
Check engine mechanical condition using a compression gauge, vacuum gauge or engine analyzer capable of performing a relative compression test. If using engine analyzer, see engine analyzer instruction manual for availability and description of relative compression feature.
| WARNING | Because fuel injectors on many models are triggered by ignition switch during cranking mode, DO NOT use ignition switch during compression tests. Use a remote starter to crank engine to prevent fire hazard or engine's oiling system contamination. |
Exhaust System Backpressure
Before replacing any components, check exhaust system for restrictions. Use a vacuum gauge or a low-pressure (1-5 psi) pressure gauge to check exhaust system.
If using a vacuum gauge, connect gauge to intake manifold vacuum, and start engine. Observe gauge while holding throttle steady at 2000-2500 RPM. If vacuum gauge reading slowly drops after stabilizing, exhaust system may be restricted.
- Check At Oxygen Sensor Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound before installation.
- Diagnosis
- Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM. Note gauge. Exhaust system is restricted if reading exceeds 1.25 psi (.09 kg/cm 2 ).
- Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exists, check for restricted catalytic converter. Replace as required.
A-3, NO-START DIAGNOSIS
Note. For diesel information, see appropriate TESTS W/CODES - DIESEL and TESTS W/O CODES - 6.5L DIESEL article in the ENGINE PERFORMANCE section below.
- «TESTS W/CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon)
- «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)
DEFINITION
No-start is defined as engine cranks okay but does not start. Engine may fire a few times.
Note. Before performing following tests, check battery condition, engine cranking speed and fuel supply.
FUEL PUMP FLOW TEST
- Disconnect fuel line at fuel filter inlet. Disconnect fuel injection pump electric shut-off solenoid wire (Pink).
- Crank engine 15 seconds. If fuel pump does not supply about 1/2 pint of fuel in 15 seconds, go to «FUEL SYSTEM PRESSURE TEST»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing-65l-diesel__fuel-system-pressure-test) .
FUEL SYSTEM PRESSURE TEST
- Turn engine off. Disconnect fuel line at inlet to fuel filter assembly. Install low pressure fuel gauge to fuel line.
- Crank or run engine 10-15 seconds. If fuel pressure is not 5.8-8.7 psi (.41-.61 kg/cm 2 ), check fuel lines and fuel tank sending unit for restriction. If fuel lines and sending unit are okay, replace fuel pump.
DIAGNOSTIC CIRCUIT CHECK
Note. For information on diagnostic system check and retrieving codes, see appropriate TESTS W/CODES - DIESEL article below.
- «TESTS W/CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon)
- «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)
Preliminary Inspection
- Check all vacuum hoses for incorrect routing, restrictions, cuts and other damage. Inspect hoses beneath air cleaner assembly and other engine components.
- Inspect all wires in engine compartment for correct and good connections. Also check wires for pinched or chaffed spots, as well as contact with sharp edges or exhaust manifolds. (Scheme 224)- (Scheme 228).
- Perform preliminary inspection carefully and thoroughly. A thorough inspection can often identify cause of problem without further diagnosis.
Diagnostic Procedure
- Ensure all engine systems not related to Diesel Electronic Control (DEC) system are operating properly. DO NOT proceed with testing unless all problems not related to DEC system have been repaired. DEC system diagnosis should always begin with DIAGNOSTIC SYSTEM CHECK chart under DIAGNOSTIC CHARTS in the appropriate TESTS W/CODES - DIESEL article below. Performing this check determines whether DEC system and PCM are working properly. «TESTS W/CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon) «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)
- If trouble codes (other than Code 12) are displayed, determine whether codes are hard or intermittent trouble codes. A hard code remains until code-setting condition is repaired. Hard codes cause Malfunction Indicator Light (MIL) to come on.
- An intermittent code does not reset itself and is not present when vehicle is repaired. An intermittent code is often caused by loose connections. MIL goes out 10 seconds after fault goes away.
Scheme 224
Scheme 225
Scheme 226
Scheme 227
Scheme 228
SUMMARY
If faults were not found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to appropriate TESTS W/CODES article below. If no hard codes are found in self-diagnostics, or vehicle does not have a self-diagnostic system, proceed to TESTS W/O CODES - 6.5L DIESEL article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.
- «TESTS W/CODES - 6.5L DIESEL»(/gmc/suburban/i-1992-1999/remont/testing-diagnostics/#engine-controls-tests-wcodes-65l-diesel) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon)
- «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)
