Engine Controls - Tests W/codes - Tests: Other Isuzu Oasis I

CIRCUIT TESTS

Note. Before performing any diagnostic test, refer to TESTS W/CODES - INTRODUCTION article for diagnostic system functions and system diagnostic procedures.

Note. When there is no DTC stored, MIL will stay on if the SCS service connector is connected and ignition switch is on.

When directed by testing procedure to install test equipment, see TEST EQUIPMENT in TESTS W/CODES - INTRODUCTION article.

Malfunction Indicator Light (MIL) Never Comes On, Even For 2 Seconds, After Ignition Is Turned On

1. Turn ignition on. If low oil pressure light is on, go to next step. If light is not on, repair short or open in Yellow wire between No. 1 BACK UP, LIGHTS, METER LIGHTS, TURN SIGNALS (10-amp) fuse and gauge assembly. Replace No. 1 fuse. See WIRING DIAGRAMS article.
2. Try to start engine. If engine does not start, go to next step. If engine starts, turn ignition off. Using a fused jumper wire, ground PCM 32-pin connector "A" terminal A18 (Blue wire). see scheme 1 Turn ignition on. If MIL comes on, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM. If MIL does not come on, replace MIL bulb and/or repair open in Blue wire between PCM and gauge assembly 10-pin Blue connector terminal No. 7. See WIRING DIAGRAMS article.
3. Check No. 33 ECU/PCM (15-amp) fuse located in underhood fuse/relay box. If fuse is blown, replace fuse and repair short in White/Green wire between No. 33 fuse and PGM-FI main relay terminal No. 7. See WIRING DIAGRAMS article. If fuse is okay, check No. 2 FUEL PUMP (15-amp) fuse located in underdash fuse/relay box. If fuse is blown, replace fuse and repair short in Red/White wire between No. 2 fuse and PGM-FI main relay terminal No. 5. See WIRING DIAGRAMS article. If fuse is okay, go to next step.
4. Turn ignition off. Disconnect fuel injectors and IAC valve connectors. Turn ignition on. Using backprobe kit, measure voltage between ground and PCM 25-pin connector "B" terminal B1 (Yellow/Black wire) and terminal B9 (Yellow/Black wire), individually. see scheme 2 If battery voltage exists, go to next step. If battery voltage does not exist, repair open in Yellow/Black wire(s) between PCM and PGM-FI connector terminal No. 6. If wire is okay, check for poor connections or loose wires at PGM-FI connector. Repair as necessary. See WIRING DIAGRAMS article. If connections and wires are okay, check PGM-FI main relay. See «SYSTEM/COMPONENT TESTS»(ref-16351) article.
5. Ensure ignition is on. Using backprobe kit, measure voltage between ground and PCM 25-pin connector "B" terminal B2 (Black wire), B10 (Black wire), B20 (Brown/Black wire) and terminal B22 (Brown/Black wire), individually. see scheme 2 If less than one volt exists, go to next step. If one volt or more exists, repair open in suspect wire(s) between PCM and ground connection G101 located at end of intake manifold, under Intake Air Temperature (IAT) sensor. See WIRING DIAGRAMS article.
6. Ensure ignition is on. Using backprobe kit, measure voltage between ground and PCM 31-pin connector "C" terminal C19 (Yellow/Red wire) and C28 (Yellow/Blue wire), individually. see scheme 3 See WIRING DIAGRAMS article. On Yellow/Red wire, if about 5.0 volts does not exist, go to next step. On Yellow/Blue wire, if about 5.0 volts does not exist, go to step 8). If about 5.0 volts exists at both circuits, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.
7. Measure voltage between ground and PCM 31-pin connector "C" terminal C19 (Yellow/Red wire). Disconnect MAP sensor. If about 5.0 volts exists when sensor is disconnected, replace MAP sensor. If about 5.0 volts does not exist, repair short in Yellow/Red wire between sensor and PCM. See WIRING DIAGRAMS article.
8. Measure voltage between ground and PCM 31-pin connector "C" terminal C28 (Yellow/Blue wire). Disconnect EGR valve, Fuel Tank Pressure (FTP) sensor and TP sensor, one at a time. If about 5.0 volts exists when sensor is disconnected, replace suspect sensor. If about 5.0 volts does not exist, repair Yellow/Blue wire between suspect sensor and PCM. See WIRING DIAGRAMS article. NOTE: When there is no DTC stored, MIL will stay on if the SCS service connector is connected and ignition switch is on.

Malfunction Indicator Light (MIL) Stays On Or Comes On After 2 Seconds

1. If symptom is intermittent, check for: An intermittent short in Red wire between PCM 32-pin connector "A" terminal A10 and 2-pin Blue service check connector. See WIRING DIAGRAMS article. An intermittent short in Blue wire between PCM 32-pin connector "A" terminal A18 and gauge assembly. See WIRING DIAGRAMS article. Perform repairs as necessary and recheck MIL operation. If no problems are found, go to next step.
2. Connect OBD-II scan tool to DLC connector located under instrument panel on right side of center console. Turn ignition on. Check for DTCs. See «RETRIEVING CODES»(ref-16345-S38702527312000122900000) in TESTS W/CODES - INTRODUCTION article. If DTCs do not exist, go to next step. If DTCs exist, perform appropriate test. See «DIAGNOSTIC TROUBLE CODE IDENTIFICATION»(ref-16349-S12148616672002082300000). After identifying DTC, go to Diagnostic Trouble Code (DTC) test.
3. Turn ignition off. Connect SCS Service Connector (07PAZ-0010100) to service check connector located under instrument panel, on right side of center console. See «TESTS W/CODES - INTRODUCTION»(ref-16345) article. Turn ignition on. If MIL does not indicate DTCs exist, go to next step. If MIL indicates DTCs exist, repair open or short in Light Green wire between PCM 32-pin connector "A" terminal A21 and DLC. see scheme 1and see scheme 5. See WIRING DIAGRAMS article. If DTCs exist, perform appropriate test. See «DIAGNOSTIC TROUBLE CODE IDENTIFICATION»(ref-16349-S12148616672002082300000). After identifying DTC, go to Diagnostic Trouble Code (DTC) test.
4. Attempt to start engine. If engine starts, go to next step. If engine does not start, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.
5. Turn ignition off and then turn ignition on. Using a backprobe kit, measure voltage between ground and PCM 32-pin connector "A" terminal A10 (Red wire). see scheme 1 If battery voltage exists, go to next step. If battery voltage does not exist, repair short to ground in Red wire between PCM and DLC. See WIRING DIAGRAMS article.
6. Turn ignition off. Disconnect PCM 32-pin connector "A". Turn ignition on. If MIL is on, repair short to ground in Blue wire between PCM 32-pin connector "A" terminal A18 and MIL. See WIRING DIAGRAMS article. If MIL is not on, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.

Scheme 25

1. Turn ignition on. Check MAP sensor using OBD-II scan tool. If about zero in. Hg or 2.8 volts is indicated, go to next step. If about zero in. Hg or 2.8 volts is not indicated, problem is intermittent. System is okay at this time. Check for poor connections or loose wires at MAP sensor and PCM connectors. See WIRING DIAGRAMS article.
2. Turn ignition off and disconnect MAP sensor 3-pin connector. Turn ignition on. Check MAP sensor using OBD-II scan tool. If about zero in. Hg or 2.8 volts is indicated, go to next step. If about zero in. Hg or 2.8 volts is not indicated, replace MAP sensor.
3. Measure voltage between MAP sensor harness connector terminals No. 1 (Yellow/Red wire) and No. 2 (Green/White wire). (Scheme 25) If about 5.0 volts exists, go to next step. If about 5.0 volts does not exist, repair open in Yellow/Red wire between PCM 31-pin connector "C" terminal C19 and MAP sensor. See WIRING DIAGRAMS article.
4. Turn ignition off. Disconnect PCM 31-pin connector "C". Check for continuity between ground and MAP sensor 3-pin harness connector terminal No. 3 (Red/Green wire). (Scheme 25) If continuity exists, repair short in Red/Green wire between PCM and MAP sensor. See WIRING DIAGRAMS article. If continuity does not exist, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.

Random Misfire Occurs During Low RPM & Low Engine Load

Check for

1. Correct IAC valve operation.
2. MAP sensor poor response.
3. EGR system malfunction.
4. Correct fuel pressure. See FUEL SYSTEM in «BASIC TESTING»(ref-16344) article.
5. Correct valve adjustment. See «ADJUSTMENTS»(ref-16352) article.
6. Crankshaft position sensor malfunction.

Random Misfire Occurs During Acceleration

Check for

1. Worn or broken spark plug wires.
2. Worn or damaged distributor ignition housing.
3. Correct fuel pressure. See FUEL SYSTEM in «BASIC TESTING»(ref-16344) article.
4. Malfunctioning Ignition Control Module (ICM). See «SYSTEM/COMPONENT TESTS»(ref-16351) article.
5. MAP sensor poor response.

Random Misfire Occurs During High Engine RPM & Load Conditions

Check for

1. Correct fuel pressure. See FUEL SYSTEM in «BASIC TESTING»(ref-16344) article.
2. Worn or broken spark plug wires.
3. Worn or damaged distributor ignition housing.
4. Malfunctioning Ignition Control Module (ICM). See «SYSTEM/COMPONENT TESTS»(ref-16351) article.
5. MAP sensor poor response.
6. Crankshaft position sensor malfunction.
7. Correct valve adjustment. See «ADJUSTMENTS»(ref-16352) article.

Random Misfire Occurs Under Nonspecific Conditions

Check for

1. Correct fuel pressure. See FUEL SYSTEM in «BASIC TESTING»(ref-16344) article.
2. Worn or broken spark plug wires.
3. Worn or damaged distributor ignition housing.
4. MAP sensor poor response.
5. Malfunctioning Ignition Control Module (ICM). See «SYSTEM/COMPONENT TESTS»(ref-16351) article.
6. Crankshaft position sensor malfunction.
7. Correct valve adjustment. See «ADJUSTMENTS»(ref-16352) article.

Other Possible Causes

Check for

1. Insufficient fuel pump pressure or flow.
2. Clogged, blocked or leaking fuel line.
3. Clogged fuel filter.
4. Fuel pressure regulator stuck open.
5. EGR system malfunction.
6. Distributor malfunction.
7. Ignition coil wire leaking or open.
8. ICM malfunction.
9. MAP sensor poor response or range/performance problem.
10. Carbon deposits on valves.
11. Low cylinder compression.
12. IAC valve malfunction.
13. VTEC system malfunction.
14. Low fuel quality (inadequate octane level).