SYMPTOM DIAGNOSIS
Note. Recommended procedures for listed symptoms are given in numbers from 1 to 28. See SYMPTOM PROCEDURE DEFINITION.
Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC TESTING and/or appropriate information in TESTS W/CODES articles were performed before diagnosing a symptom. Following symptoms are available for diagnosis
- Hard Start/Will Not Start
- High Idle
- Unstable Idling
- Hesitation
- Poor Driveability
- Engine Stall
- Backfire
SYMPTOM PROCEDURE DEFINITION
Recommended procedures (specified numerically) are as follows. These steps help determine and rectify cause of specific symptom.
1
Ensure fuel pressure is within specification.
2
See appropriate INJECTOR MALFUNCTION diagnostic chart in I - SYS/COMP TESTS article.
3
Inspect throttle body ports and valves for deposits, wear and plugging. Clean or replace as necessary.
4
Check for spark using spark tester.
5
Check idle speed control circuit. See IDLE CONTROL SYSTEM in I - SYS/COMP TESTS article.
6
Ensure battery and charging system are okay.
7
Check spark plug for improper gap and fouling.
8
Ensure intake system does not have vacuum leaks.
9
Disconnect oxygen sensor connector(s). Run engine at 2000 RPM for 30 seconds. Return to idle. If idle RPM decreases, repair intake system air leak.
10
Check EGR control valve operation.
11
Check EGR control valve solenoid operation.
12
Ensure engine has adequate compression.
13
Disconnect exhaust gas sensor connector(s). If symptom is no longer present, check exhaust gas sensor operation. See appropriate TESTS W/CODES article.
14
Disconnect and plug canister purge line. If symptom is no longer present, check purge and vacuum lines.
15
Disconnect vacuum hose from fuel pressure regulator. If symptom is no longer present, check for vapor-locked fuel.
16
Check fuel level.
17
Check ECM harness connector.
18
Try a known good ECM.
19
Check ECM power source and ground circuit. See appropriate ECM POWER SOURCE & GROUND diagnostic chart in appropriate I - SYS/COMP TESTS article.
20
Check timing belt for proper installation.
21
Check throttle linkage operation.
22
Try a known good airflow meter.
23
Check for intake valve deposits.
24
Check engine temperature sensor. See I - SYS/COMP TESTS
article.
25
Perform power balance test.
26
Ensure fast idle cam holds throttle valve open.
27
With engine idling, disconnect AAC valve connector. If engine RPM does not decrease, check AAC valve circuit. See IDLE CONTROL SYSTEM in I - SYS/COMP TESTS article.
28
Check exhaust gas sensor operation. See TESTS W/CODES article.
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or component failure to identify problem. These procedures may lead to computer setting a fault code (on some systems) which may help in diagnosis.
If problem vehicle does not produce fault codes, monitor voltage or resistance values using a DVOM while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.
Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition is on or engine is running. Ensure ignition is off or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.
TEST PROCEDURES (ALTIMA, NX, QUEST, SENTRA, 240SX & 300ZX)
Note. For additional information on self-diagnostic system, see TESTS W/CODES article.
Two different diagnostic modes are available through ECM. Mode I is used as a bulb check and malfunction warning. Mode II is self-diagnostic system, used to obtain trouble codes for component or circuit failures. Mode II also monitors air/fuel mixture ratio by using CHECK ENGINE light and Red LED on ECM.
TEST PROCEDURES (MAXIMA, PATHFINDER & PICKUP)
Note. For additional information on self-diagnostic system, see TESTS W/CODES article.
Five different diagnostic modes are available through ECM. Diagnostic Modes I and II monitor air/fuel mixture ratio using LED inspection lights. Mode III is self-diagnostic system, used to obtain trouble codes for component or circuit failures. Mode IV monitors for malfunctions in system's on-off control switches. Mode V is real-time diagnostic system: it monitors system and its components during actual driving and is particularly sensitive to intermittent symptoms.