Engine Controls - Basic Diagnostic Procedures - 4.3l Chevrolet Blazer S15

MODEL IDENTIFICATION

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.

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.

A & C CHART REFERENCE

GENERAL MOTORS 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 VACUUM DIAGRAMS 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.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use a vacuum gauge or a low-pressure (1-5 psi) 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.

1. 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.
2. 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.

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.

General Inspection

1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.

Ignition System

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__on-board-diagnostic-obd-system-check). After performing OBD system check, go to next step.
2. Install Tech 1 scan tool. Using scan tool, monitor Throttle Position (TP) sensor voltage. Ensure is throttle closed. If TP sensor value is greater than 2.5 volts, diagnose using DTC P0123. See TESTS W/CODES article. If TP sensor voltage is less than 2.5 volts, go to next step.
3. Using scan tool, monitor Engine Coolant Temperature (ECT) sensor. If ECT sensor value is less than -30°C, diagnose using DTC P0118. See TESTS W/CODES article. If ECT sensor is greater than -30°C, go to next step.
4. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. If fuel pump operates as specified, go to next step. If fuel pump does not operate as specified, go FUEL SYSTEM check.
5. Turn ignition off. Disconnect injector harness connector at intake manifold. Using a test light connected to ground, probe injector feed circuit (Pink wire). (Scheme 31) Crank engine. If test light flashes, go to next step. If test light does not flash, go to step 8).
6. Disconnect one spark plug wire. Install Spark Tester (ST-125). Crank engine. If spark is present, go to next step. If spark is not present, diagnose enhanced ignition system.
7. Reconnect spark plug wire. Turn ignition off. Connect fuel pressure gauge. Turn ignition on and observe fuel pressure. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ). If fuel pressure is as specified, perform fuel injector balance test. See INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If fuel pressure is not as specified, «BASIC FUEL SYSTEM CHECKS»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l).
8. Repair injector ignition feed circuit (Pink wire). (Scheme 31) After repairs, go to next step.
9. Using scan tool, select DTC, CLEAR INFO function. Attempt to start engine. If engine start and continues to run, go to next step. If engine does not start or starts and dies, go to step 2).
10. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN. If DTC(s) are displayed, diagnose DTC(s). See TESTS W/CODES article. If DTC(s) are not present, go to next step.
11. Select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) are displayed, diagnose DTC(s). See TESTS W/CODES article.

Scheme 31

Fuel System

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__on-board-diagnostic-obd-system-check). After performing OBD system check, go to next step.
2. Turn ignition off for about 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. If fuel pump operates as specified, go to IGNITION SYSTEM check. If fuel pump does not operate as specified, go to next step.
3. Connect a fused jumper wire between battery positive and fuel pump test terminal. If fuel pump operates, go to next step. If fuel pump does not operate, go to step 12).
4. Disconnect jumper wire from test terminal. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. If fuel pump operates as specified, go to step 25). If fuel pump does not operate as specified, go to next step.
5. Remove fuel pump relay. Turn ignition on with engine off. Using a test light connected to ground, probe fuel pump relay harness connector battery feed terminal (Orange wire). (Scheme 32) If test light illuminates, go to next step. If test light does not illuminate, go to step 14).
6. Connect test light between ground and fuel pump relay harness connector battery feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 15).
7. Connect test light between ground and fuel pump relay terminal. Turn ignition off for 10 seconds. Turn ignition on. If test light illuminates for 2 seconds and then turns off, go to next step. If test light does not illuminate, go to step 16).
8. Check for faulty fuel pump relay harness connector. Repair as necessary. After repairs, go to step 11). If connector is okay, go to next step.
9. Replace fuel pump. After repairs, go to step 25). If fuel pump is okay, go to next step.
10. Start and warm engine to normal operating temperature. Ensure oil pressure is within normal range. Disconnect fuel pump relay. If engine continues to run, go to next step. If engine stalls/dies, go to step 17).
11. Reinstall fuel pump relay. Turn ignition off. Using a test light connected to ground, probe fuel pump test connector. If test light illuminates, go to step 18). If test light does not illuminate, go to step 25).
12. Disconnect fuel pump harness connector. Using a fused jumper wire connected to battery voltage, jumper fuel pump test terminal. Using a test light connected to ground, probe fuel pump feed circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 20).
13. Connect test light to fuel pump ground terminal on harness connector. (Scheme 32) If test light illuminates, go to step 19). If test light does not illuminate, go to step 21).
14. Repair open in battery feed circuit to fuel pump relay harness connector terminal. After repairs, go to step 25).
15. Repair open in fuel pump relay ground circuit. After repairs, go to step 25).
16. Check for faulty connection at VCM fuel pump relay control circuit. Check for open or short to ground in harness between fuel pump relay control connector terminal and fuel pump relay control circuit. (Scheme 32) Repair as necessary. After repairs, go to step 22). If circuits are okay, go to step 24).
17. Check for faulty oil pressure switch connector terminals. Repair as necessary. After repairs, go to step 22). If connector terminals are okay, go to next step.
18. Replace oil pressure switch. After repairs, go to step 25).
19. Replace fuel pump. After repairs, go to step 25).
20. Repair open between fuel pump test terminal and fuel pump feed circuit at fuel pump harness connector. After repairs, go to step 25).
21. Repair open in fuel pump harness ground circuit. After repairs, go to step 25).
22. Repair affected circuit as necessary. After repairs, go to step 25).
23. Repair connectors as necessary. After repairs, go to step 25).
24. Replace VCM. Perform VCM relearn procedures. After repairs, go to next step.
25. Clear DTC(s) using scan tool. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start or starts and stalls/dies, go to step 2).
26. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If any DTC(s) are present, diagnose DTC. See TESTS W/CODES article. If DTC(s) are not present, go to next step.
27. Select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) are displayed, diagnose DTC(s). See TESTS W/CODES article.

Scheme 32

FUEL SYSTEM PRESSURE RELIEF

Fuel system is under pressure, which must be relieved before servicing fuel system. Fuel pressure may be relieved by one of the following methods.

1. Disconnect negative battery terminal. Loosen fuel filler cap.
2. Install Fuel Pressure Gauge (J-34730-1A) to fuel pressure test head. Wrap shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage. Place gauge bleed hose in container. Open bleed valve to relieve fuel pressure.

FUEL SYSTEM PRESSURE TEST

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
2. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__fuel-system-pressure-relief) . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure test port. Turn ignition on with engine off. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm 2 ) on CSI fuel system and 56-62 psi (4.0-4.4 kg/cm 2 ) on SFI fuel system, and should hold steady.
3. Turn ignition off for 10 seconds and then turn ignition on. Fuel pump should run for 2 seconds. Observe fuel pressure. If pressure is within specification and holds, go to step 5). If pressure is not within specification or is within specification but does not hold, go to next step.
4. Turn ignition off for 10 seconds. Turn ignition on. Pinch off fuel pressure feed line. If pressure is as specified and holds, go to step 6). If pressure is not as specified or is as specified but does not hold, go to step 8).
5. Warm engine to normal operating temperature. From idle, open throttle quickly. Observe fuel pressure. If fuel pressure is within specification, see TESTS W/O CODES article. If fuel pressure is not within specification, go to step 23).
6. Check for partially disconnected fuel pulse dampener/pulsator. If dampener/pulsator is partially disconnected, go to next step. If dampener/pulsator is okay, go to step 13).
7. Repair connection at fuel pulse dampener/pulsator. After repairs, go to step 28).
8. Check fuel feed line between pinch and CSI/SFI unit. If fuel feed line is okay, go to step 23). If fuel feed line is restricted or leaking, go to step 27).
9. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. Observe fuel pressure after fuel pump stops. If pressure is present, go to step 14). If pressure is not present or drops, go to next step.
10. Turn ignition off. Connect a fused jumper wire to battery voltage. Jumper fuel pump test terminal. If fuel pump operates, go to next step. If fuel pump does not operate, see FUEL SYSTEM test in «A-3, NO-START DIAGNOSIS»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l) .
11. Check for plugged fuel filter, plugged fuel pump strainer, restricted fuel line or disconnected fuel pulse dampener/pulsator. After repairs, go to step 28).
12. Check for restricted fuel line, fuel filter, plugged fuel pump strainer or disconnected fuel pulse/pulsator. After repairs, go to step 28).
13. Replace fuel pump. After repairs, go to step 28).
14. Turn ignition off for 10 seconds and then turn ignition on. Fuel pump should operate for about 2 seconds. Observe fuel pressure. If fuel pressure is greater than 66 psi (4.6 kg/cm 2 ) on CSI fuel system or 62 psi (4.4 kg/cm 2 ) on SFI fuel system, go to next step. If fuel pressure is not greater than specified, go to step 16).
15. Relieve fuel pressure. Disconnect fuel return line. Attach a fuel hose to fuel regulator return line and place in a container. Turn ignition on. Observe fuel pressure within 2 seconds after turning on ignition. If fuel pressure is greater than 60 psi (4.2 kg/cm 2 ) on CSI fuel system or 56 psi (4.0 kg/cm 2 ) on SFI fuel system, go to step 17). If fuel pressure is less than as specified, go to step 19).
16. Turn ignition off for 10 seconds. Turn ignition on. Fuel pump should operate for about 2 seconds. Observe fuel pressure. If fuel pressure is less than 60 psi (4.2 kg/cm 2 ) on CSI fuel system or 56 psi (4.0 kg/cm 2 ) on SFI fuel system, go to step 20). If fuel pressure is greater than as specified, go to step 28).
17. Check for restricted fuel line from fuel pressure regulator to point where fuel line was disconnected. If fuel line is restricted, go to next step. If fuel line is not restricted, go to step 23).
18. Repair restriction in fuel return line from pressure regulator to the point where fuel line was disconnected. If fuel return line is restricted, go to next step. If fuel return line is not restricted, go to step 23).
19. Repair restriction in fuel return line to fuel tank. After repairs, go to step 27).
20. Check for restricted fuel line or fuel filter. After repairs, go to step 27).
21. Repair or replace restricted fuel line or fuel filter. After repairs, go to step 27). CAUTION: DO NOT allow fuel pressure to exceed 75 psi (5.3 kg/cm 2 ).
22. Turn ignition off. Connect a fused jumper wire between battery voltage and fuel pump test terminal. Slowly pinch fuel line return hose. Fuel pressure should increase to greater than 66 psi (4.6 kg/cm 2 ) on CSI fuel system or 62 psi (4.4 kg/cm 2 ) on SFI fuel system. If fuel pressure increases to greater than as specified, go to next step. If fuel pressure is less than as specified, go to step 24).
23. Replace fuel pressure regulator. After repairs, go to step 28).
24. If fuel pressure is less than 60 psi (4.2 kg/cm 2 ) on CSI fuel system or 56 psi (4.0 kg/cm 2 ) on SFI fuel system, go to next step. If fuel pressure is greater than specified, go to step 28).
25. Check for faulty fuel pump, partially disconnected fuel pulse dampener/pulsator, partially restricted fuel pump stainer or incorrect fuel pump. Repair as necessary. After repairs, go to step 26). If problem is not found, go to step 28).
26. Repair or replace fuel pump, partially disconnected fuel pulse dampener/pulsator, partially restricted fuel pump strainer or incorrect fuel pump. After repairs, go to next step.
27. Replace fuel feed/supply line. After repairs, go to next step.
28. Using scan tool, select DTC, CLEAR INFO function. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start or starts and stalls/dies, go to step 2).
29. Warm engine to normal operating temperature. Using DTC, select DTC, FAILED THIS IGN function. If any DTC(s) are displayed, diagnose and clear DTC(s). See TESTS W/CODES article. If DTC(s) are not present, go to next step.
30. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) are stored, diagnose and clear DTC(s). See TESTS W/CODES article.

INJECTOR CIRCUIT DIAGNOSIS (A-4)

Note. This test only applies to vehicles equipped with a VCM.

1. «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
2. Disconnect injector connector at intake manifold. Turn ignition on. Using test light connected to ground, probe ignition feed circuits. See WIRING DIAGRAMS article. If test light illuminates, go to next step. If test light does not illuminate, go to step 7).
3. Install injector test light to each injector circuit, one at a time. Crank engine. If injector test light flashes on each injector, check fuel injector(s). See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If injector test light did not flash on an injector circuit, go to next step.
4. If injector test light was on steady on an injector circuit, go to next step. If injector test light did not illuminate on an injector circuit, go to step 6).
5. Install injector test to affected injector. Turn ignition off. Disconnect Blue and Red VCM connectors. Turn ignition on, with engine off. If injector test light turns off, go to step 11). If injector test light stays on, go to step 8).
6. Check for open or short in battery circuit to affected injector. If circuit is open or shorted, go to next step. If circuit is okay, go to step 9).
7. Repair circuit as necessary. After repairs, go to step 12).
8. Repair short to ground in injector control circuit. After repairs, go to step 12).
9. Check terminal contact at VCM connector. If terminal contact is faulty, go to next step. If terminal contact is okay, go to step 11).
10. Repair terminal contact. After repairs, go to step 12).
11. Replace VCM. Reprogram replacement VCM. After replacing VCM, go to next step.
12. Using scan tool, select DTC, CLEAR INFO mode. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start or starts and stalls/dies, go to step 14).
13. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN mode. If other DTC(s) are present, diagnose affected DTC(s). If no other DTC(s) are present, go to next step.
14. Using scan tool, select CAPTURE INFO, REVIEW INFO. If additional undiagnosed DTC(s) are present, diagnose affected DTC(s). If DTC(s) are not present, system is okay.

C-4, BASIC IGNITION SYSTEM CHECKS

Note. To diagnose ignition system, see appropriate IGNITION SYSTEM test in A-3, NO-START DIAGNOSIS .

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specifications. For specifications, see SPECIFICATIONS article. For adjustment procedures, see ADJUSTMENTS article.

ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK

Note. Use of Tech 1 scan tool is required to perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK.

THE OBD SYSTEM CHECK DETERMINES

1. If Malfunction Indicator Light (MIL) works.
2. If PCM/VCM is operating and can recognize a fault.
3. If any Diagnostic Trouble Codes (DTCs) are stored.

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in the OBD system circuit check, if no codes are indicated and driveability problems still exist, see TESTS W/O CODES article and SCAN TESTER usage in TESTS W/CODES article.

1. Turn ignition on with engine off. Observe Malfunction Indicator Light (MIL). If MIL illuminates, go to next step. If MIL does not illuminate, go to «A-1, MALFUNCTION INDICATOR LIGHT (MIL)»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__a-1-malfunction-indicator-light-mil) .
2. Turn ignition off. Install Tech 1 scan tool and follow scan tool manufacturer's instructions to proceed with test. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to «A-2, NO SCAN TOOL DATA»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__a-2-no-scan-tool-data) .
3. Attempt to start engine. If engine starts and runs, go to next step. If engine does not start or starts and dies, see «A-3, NO-START DIAGNOSIS»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l) . Repair as necessary.
4. Using scan tool, observe DTC status LAST TST FAIL function. If any DTC is stored, save freeze frame and fail record information using CAPTURE INFO feature. If a DTC is indicated as last test failed, diagnose affected DTC. See TESTS W/CODES article. If DTC is not indicated, go to next step.
5. Using scan tool, display DTC fail records. If a DTC fail record is stored, save freeze frame and fail record information using scan tool CAPTURE INFO feature. If a fail record is stored, diagnose affected DTC. See TESTS W/CODES article.

Scheme 33

A-1, MALFUNCTION INDICATOR LIGHT (MIL)

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__on-board-diagnostic-obd-system-check). After performing OBD system check, go to next step.
2. Turn ignition on with engine off. If Malfunction Indicator Light (MIL) illuminates, go to step 4). If MIL does not illuminate, go to next step.
3. Start engine. If engine starts, go to step 5). If engine does not start, go to step 6).
4. Install Tech 1 scan tool. Turn ignition on. Using scan tool, command MIL to turn on and off. If MIL turns on and off as commanded, go to step 22). If MIL does not turn on and off as commanded, go to next step.
5. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Using a test light connected to ground, probe MIL driver circuit (Brown/White wire). (Scheme 33) If MIL illuminates, go to step 7). If MIL does not illuminate, go to step 8).
6. Inspect ignition and battery fuses. If fuses are okay, go to step 9). If fuses are faulty, go to step 10).
7. Using a test light connected to ground, probe PCM harness connector ignition feed terminal No. 2 (Purple wire). (Scheme 33) If test light illuminates, go to step 11). If test light does not illuminate, go to step 12).
8. If test light illuminated, go to step 13). If test light did not illuminate, go to step 14).
9. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a test light connected to ground, probe PCM harness connector ignition feed circuit No. 1 (Pink wire). (Scheme 33) If test light illuminates, go to step 18). If test light does not illuminate, go to step 19).
10. Check for short to ground in fuse circuit that was open. Repair as necessary and replace fuse. After repairs, go to step 22).
11. Check for faulty PCM connections. If connections are okay, replace PCM. After repairs, go to step 22).
12. Repair open in ignition feed circuit No. 2 (Pink wire). (Scheme 33) After repairs, go to step 22).
13. Repair short to voltage in MIL control circuit (Brown/White wire). (Scheme 33) After repairs, go to step 22).
14. Check for open in MIL control circuit. (Scheme 33) Repair as necessary. After repairs, go to step 22). If circuit is okay, go to next step.
15. Check for open in ignition feed circuit or fuse to MIL. (Scheme 33) Repair as necessary. After repairs, go to step 22). If circuit or fuse is okay, go to next step.
16. Check for an open MIL bulb. If light bulb is faulty, go to step 22). If light bulb is okay, go to next step.
17. Replace instrument panel assembly. After replacing instrument panel, go to step 22).
18. Using test light connected to ground, probe battery feed circuit (Orange wire). (Scheme 33) If test light illuminates, go to step 20). If test light does not illuminate, go to step 21).
19. Repair open in ignition feed circuit No. 1 (Pink wire). (Scheme 33) After repairs, go to step 22).
20. Check for faulty PCM ground connection at engine block. After repairs, go to step 22). If connections were okay, go to step 11).
21. Repair open in battery feed circuit (Orange wire). (Scheme 33) After repairs, go to next step.
22. Using scan tool, clear DTC(s) stored. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start or starts and dies/stalls, go to step 1).
23. Warm engine to normal operating temperature. Check if any DTC(s) are set. Diagnose any DTC present. See TESTS W/CODES article.

A-2, NO SCAN TOOL DATA

1. Perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__on-board-diagnostic-obd-system-check). After performing OBD system check, go to next step.
2. Turn ignition off for 30 seconds. Turn ignition on with engine off. Observe MIL. If MIL illuminates, go to next step. If MIL does not illuminate, go to «A-1, MALFUNCTION INDICATOR LIGHT (MIL)»(/chevrolet/blazer/s15-1994-1998/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures-43l__a-1-malfunction-indicator-light-mil).
3. Install scan tool. If scan tool communicates with VCM, go to next step. If scan tool does not communicate with VCM, go to step 5).
4. Using scan tool, command MIL to turn on and off. If MIL turns on and off as commanded, go to step 17). If MIL does not turn on or off as commanded, go to next step.
5. Turn ignition off. Disconnect VCM connectors. Turn ignition on. Observe MIL. If MIL illuminates, go to step 18). If MIL does not illuminate, go to next step.
6. Using scan tool, check engine calibration ID. If proper ID is displayed, go to step 28). If proper ID not displayed, go to step 19).
7. Connect a test light to ground. Using test light, probe DLC terminal No. 16. (Scheme 33) If test light illuminates, go to next step. If test light does not illuminate, go to step 20).
8. Connect a test light to battery voltage. Using test light, probe DLC terminals No. 4 and 5. If test light illuminates on both circuits, go to next step. If test light does not illuminate on either circuit, go to step 21).
9. Check cigarette lighter for power. If power is present at cigarette lighter, go to next step. If power is not present at cigarette lighter, go to step 22).
10. Install and check scan tool on another vehicle. If scan tool works, go to next step. If scan tool does not work, go to step 23).
11. Disconnect scan tool. Using DVOM, check voltage between ground and VCM serial data line at DLC terminal No. 2. (Scheme 33) DVOM should read 7 volts. If voltage is less than 7 volts, go to next step. If voltage is 7 volts or greater, go to step 15).
12. Using DVOM, again check voltage between ground and DLC terminal No. 2. DVOM should read 1 volt. If voltage is less than 1 volt, go to next step. If voltage is 1 volt or greater, go to step 27).
13. Turn ignition off. Using DVOM, check resistance between ground and DLC terminal No. 2. Resistance should be 10 ohms. If resistance is less than 10 ohms, go to next step. If resistance is 10 ohms or greater, go to step 27).
14. Disconnect VCM connectors. Using DVOM, check resistance between ground and DLC terminal No. 2. Resistance should be 10 ohms. If resistance is less than 10 ohms, go to step 24). If resistance is 10 ohms or greater, go to step 26).
15. Turn ignition off. Disconnect VCM connectors. Turn ignition on. Check voltage on DLC terminal No. 2. Voltage should not be present. If voltage is not as specified, go to step 25). If voltage is as specified, go to step 27).
16. Reprogram EEPROM and retest. If serial data is present, go to step 27). If serial data is not present, go to step 26).
17. System is okay. Proceed to step 27).
18. Repair short to ground in MIL control circuit (Brown/White wire). (Scheme 33) After repairs, go to step 27).
19. Reprogram EEPROM and retest. After repairs, go to step 27).
20. Check fuse No. 7 (PWR AUX). If fuse is faulty, repair short to ground in DLC terminal No. 16 circuit (Orange wire). If fuse is okay, repair open in DLC terminal No. 16 circuit (Orange wire). After repairs, go to step 27).
21. Repair open in affected circuit. After repairs, go to step 27).
22. Repair cigarette lighter circuit. After repairs, go to step 27).
23. Repair or replace faulty scan tool and/or cables. After repairs, go to step 27).
24. Repair short to ground in serial data line (Purple wire). After repairs, go to step 27).
25. Repair short to voltage in serial data line (Purple wire). After repairs, go to step 27).
26. Check for open in serial data line. If circuit is okay, check VCM and DLC connectors. If connectors are okay, replace VCM. Perform VCM relearn procedures. After repairs, go to next step.
27. Using scan tool, select DTC, CLEAR INFO function. Attempt to start engine. If engine starts and continues to run, go to next step. If engine does not start or starts and dies/stalls, go to step 2).
28. Warm engine to normal operating temperature. Using scan tool, select DTC, FAILED THIS IGN function. If any DTC(s) are stored, diagnose DTC. See TESTS W/CODES article. If DTC(s) are not present, go to next step.
29. Select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) are displayed, diagnose DTC. See TESTS W/CODES article.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, no trouble codes (or only intermittent ones) were found while performing ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK and driveability problems exist, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.

See also:
• ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
• A-3, NO-START DIAGNOSIS
• FUEL SYSTEM PRESSURE RELIEF
• A-1, MALFUNCTION INDICATOR LIGHT (MIL)
• A-2, NO SCAN TOOL DATA