Self-Diagnostic System
The self-diagnostic system is used to diagnosis malfunctions in major sensors and actuators of the ECCS system. There are five modes in the self-diagnostic system:
1. Mode I (Mixture ratio feedback control monitor A): During a closed loop condition, the green inspection lamp turns On when lean condition is present and goes Off when a rich condition is present. During a open loop condition, the green inspection lamp stays Off.
2. Mode II (Mixture ratio feedback control monitor B): During a closed loop condition, the red inspection lamp turns On and Off simultaneously with the green inspection lamp when mixture ratio is controlled within a predetermined value. During a open loop condition, the red inspection lamp stays Off. The green inspection lamp function is the same as Mode I.
3. Mode III (Self-diagnosis): This mode functions the same as previous models.
4. Mode IV (Switches ON/OFF diagnosis): During this mode, the inspection lamps monitor switch ON/OFF condition of the throttle valve switch, starter switch and vehicle speed sensor.
5. Mode V (Real time diagnosis): If a malfunction is present during a driving test, the inspection lamps will display the malfunction condition immediately.
Fig. 47 Typical ECCS control unit:
SWITCHING MODES
1. Place ignition switch in On position.
2. On all models exc. Pathfinder, Pickup and Van, proceed as follows:
a. Turn diagnostic mode selector on ECU fully clockwise and wait until inspection lamps flash, Fig. 47. Number of flashes displayed indicates corresponding Mode.
b. Note number of flashes, then immediately turn diagnostic mode selector fully counterclockwise.
3. On Pathfinder, Pickup & Van, proceed as follows:
a. Turn diagnostic mode selector on ECU to the ON position and wait until inspection lamps flash.
b. Note number of flashes, then immediately turn diagnostic mode selector to the OFF position.
4. On all models, when ignition switch is turned Off during diagnosis, in each Mode, and then turned back on again after power to the ECU has dropped off completely, diagnosis will automatically return to Mode I.
5. Stored memory will be erased if battery terminal is disconnected or after selecting Mode III or Mode IV. If diagnostic mode selector is kept turned fully clockwise, it will continue to change the Mode in sequential order and memory will not be erased.
Fig. 159 Modes I & II display indications.:
Fig. 160 Modes I & II display indications.:
MODES I & II
In these Modes, the control unit monitors Air/Fuel ratio and Air/Fuel ratio feedback coefficient. Refer to charts, Figs. 159 and 160, for display indications.
MODE III
The ECU constantly monitors the function of various sensors and actuators, regardless of ignition key position. If a malfunction is present, it is stored in the ECU and can be retrieved from memory by turning on diagnostic mode selector, located on the side of the ECU. When activated, malfunction is indicated by a series of flashing red and green light emitting diodes, also located on the ECU. When displaying malfunction codes, then code number can be determined by counting the number of light pulses. The red light represents the first digit of the code, while the green light represents the second digit of the code. For example, a Code 12 would be displayed as one flash of the red light, followed by two flashes of the green light.
Malfunction codes can be translated using the following decoding chart:
1. Code 11 -- Crank angle sensor circuit malfunction.
2. Code 12 -- Air flow meter circuit malfunction.
3. Code 13 -- 200SX w/VG30E engine, Pathfinder & Pickup w/VG30i engine, Maxima & 300ZX. Cylinder head temperature sensor circuit malfunction.
4. Code 13 -- 200SX w/CA20E engine, Pathfinder & Pickup w/Z24i engine, Pulsar, Sentra, Stanza, Stanza Wagon & Van. Water temperature sensor circuit malfunction.
5. Code 21 -- Ignition signal missing in primary coil.
6. Code 22 -- Maxima, Stanza, Stanza Wagon, 200SX & 300ZX. Fuel pump circuit malfunction.
7. Code 22 -- Pulsar & Sentra w/E16i engine. Idle speed control slips out.
8. Code 33 -- Pulsar & Sentra w/E16i engine, Pathfinder, Pickup & Van. Exhaust gas sensor circuit malfunction.
9. Code 34 -- Pulsar w/CA16DE engine, Maxima & 300ZX. Detonation sensor circuit malfunction.
10. Code 41 -- 200SX w/VG30E engine, Maxima & 300ZX. Fuel temperature sensor circuit malfunction.
11. Code 41 -- Pulsar & Sentra w/E16i engine, 200SX w/CA20E engine, Stanza & Stanza Wagon. Air temperature sensor circuit malfunction.
12. Code 42 -- Pulsar & Sentra w/E16i engine, Pathfinder, Pickup & Van. Throttle sensor circuit malfunction.
13. Code 43 -- Pulsar & Sentra w/E16i engine. Mixture ratio feedback control slips out.
14. Code 43 -- Pathfinder, Pickup & Van. Injector circuit malfunction.
15. Code 44 -- All monitored systems satisfactory.
The diagnostic code retained in the ECU will automatically be erased after starter is operated for 50 times.