Nissan Maxima 1993-1998 Repair Guide

Reading Codes

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See Figures 1 and 2



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Fig. Fig. 1: Use a flathead screwdriver to turn the diagnostic test mode selector on the ECM



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Fig. Fig. 2: The Malfunction Indicator Lamp (MIL) is located on the instrument panel

Two types of diagnostic systems are used in Nissan vehicles: the two-mode diagnostic system and the five-mode diagnostic system. The five-mode system is used in 1993-94 Maximas with VG30E engines. All other vehicles use the two-mode system.

FIVE MODE DIAGNOSTIC SYSTEM



The five-mode diagnostic system is incorporated in the ECM which uses inputs from various sensors to determine the correct air/fuel ratio. If any of the sensors malfunction the ECM will store the code in memory. The five-mode diagnostic system is capable of various tests as outlined below. When using these modes, the ECM may have to be removed from its mounting bracket to better access the mode selector switch. Vehicles are equipped with a Malfunction Indicator Light (MIL) light on the instrument panel. If any systems are malfunctioning, the (MIL) light will illuminate simultaneously with the red lamp on the ECM while the engine is running and the system is in Mode 1.

Mode I-Heated Oxygen Sensor

During closed loop operation the green lamp turns ON when a lean condition is detected and turns OFF under a rich condition. During open loop the green lamp remains ON or OFF. This mode is used to check Heated Oxygen sensor functions for correct operation. To enter Mode I, proceed as follows:

  1. Turn the ignition switch ON.
  2.  
  3. Turn the diagnostic switch located on the side of the ECM ON by either flipping the switch to the ON position or turning the screw switch fully clockwise.
  4.  
  5. Turn the diagnostic switch OFF or fully counterclockwise as soon as the inspection lamp flashes once.
  6.  
  7. The self-diagnostic system is now in Mode I.
  8.  

Mode II-Mixture Ratio Feedback Control Monitor

The green inspection lamp is operating in the same manner as in Mode I. During closed loop operation the red inspection lamp turns ON and OFF simultaneously with the green lamp when the mixture ratio is controlled within the specified value. During open loop the red lamp remains ON or OFF. Mode II is used for checking that optimum control of the fuel mixture is obtained. To enter Mode II, proceed as follows:

  1. Turn the ignition switch ON.
  2.  
  3. Turn the diagnostic switch ON, by either flipping the switch to the ON position or use a screwdriver and turn the switch fully clockwise.
  4.  
  5. Turn the diagnostic switch OFF or fully counterclockwise as soon as the inspection lamps flash twice.
  6.  
  7. The self-diagnostic system is now in Mode II.
  8.  

Mode III-Self-Diagnosis System

This mode of the self-diagnostics is for stored code retrieval.

To enter Mode III, proceed as follows:

  1. Thoroughly warm the engine before proceeding. With the engine OFF, turn the ignition switch ON.
  2.  
  3. Turn the diagnostic switch located on the side of the ECM ON by either flipping the switch to the ON position or using a screwdriver, turn the switch fully clockwise.
  4.  
  5. Turn the diagnostic switch OFF or fully counterclockwise as soon as the inspection lamps flash three times.
  6.  
  7. The self-diagnostic system is now in Mode III.
  8.  

When the battery is disconnected or self-diagnostic Mode IV is selected after using Mode III, all stored codes will be cleared. However if the ignition key is turned OFF and then the procedure is followed to enter Mode IV directly, the stored codes will not be cleared.

  1. The codes will now be displayed by the red and green inspection lamps flashing. The red lamp will flash first and the green lamp will follow. The red lamp is the tens and the green lamp is the units, that is, the red lamp flashes once and the green lamp flashes twice, this would indicate a Code 12.
  2.  

Mode IV-On/Off Switches

This mode checks the operation of the Vehicle Speed Sensor (VSS), Closed Throttle Position (CTP) and starter switches. Entering this mode will also clear all stored codes in the ECM. To enter Mode IV, proceed as follows:

  1. Turn the ignition switch ON.
  2.  
  3. Turn the diagnostic switch located on the side of the ECM ON by either flipping the switch to the ON position or turning the mode switch fully clockwise.
  4.  
  5. Turn the diagnostic switch OFF or fully counterclockwise as soon as the inspection lamps flash 4 times.
  6.  
  7. The self-diagnostic system is now in Mode IV.
  8.  
  9. Turn the ignition switch to the START position and verify the red inspection lamp illuminates. This verifies that the starter switch is working.
  10.  
  11. Depress the accelerator and verify the red inspection lamp goes OFF. This verifies that the CTP switch is working.
  12.  
  13. Raise and properly support the vehicle and verify the lamp goes ON when the vehicle speed is above 12 mph (20 km/h). This verifies that the VSS is working.
  14.  
  15. Turn the ignition switch OFF.
  16.  

Mode V-Real Time Diagnostics

In this mode the ECM is capable of detecting and alerting the technician the instant a malfunction in the crank angle sensor, air flow meter, ignition signal or the fuel pump occurs while operating/driving the vehicle. Items which are noted to be malfunctioning are not stored in the ECM's memory. To enter Mode V, proceed as follows:

  1. Turn the ignition switch ON.
  2.  
  3. Turn the diagnostic switch located on the side of the ECM ON by either flipping the switch to the ON position or by turning the switch fully clockwise.
  4.  
  5. Turn the diagnostic switch OFF or fully counterclockwise as soon as the inspection lamps flash 5 times.
  6.  
  7. The self-diagnostic system is now in Mode V.
  8.  
  9. Ensure the inspection lamps are not flashing. If they are, count the number of flashes within a 3.2 second period:

    1 Flash = Camshaft position sensor
     
    2 Flashes = Air flow meter
     
    3 Flashes = Fuel pump
     
    4 Flashes = Ignition signal
     

  10.  

TWO MODE DIAGNOSTIC SYSTEM



The 2-mode diagnostic system incorporated in the ECM which uses inputs from various sensors to determine the correct air/fuel ratio. If any of the sensors malfunction the ECM will store the code in memory. The Malfunction Indicator Light (MIL) or the red LED on the ECM is used for self-diagnostics. The 2-Mode diagnostic system is broken into two separate modes, each capable of two tests, with the ignition switch in the ON position or with the engine running.

Mode I
BULB CHECK (IGNITION ON)

In this mode the RED indicator light on the ECM and the MIL light should be ON. To enter this mode simply turn the ignition switch ON and observe the light.

MALFUNCTION WARNING (ENGINE RUNNING)

In this mode the ECM is acknowledging if there is a malfunction by illuminating the RED indicator light on the ECM and the MIL light. If the light turns OFF, the system is normal. To enter this mode, simply start the engine and observe the light. In this mode the ECM will output all malfunctions via the MIL light or the red LED on the ECM. The code may be retrieved by counting the number of flashes. The longer flashes indicate the first digit and the shorter flashes indicate the second digit.

Mode II
SELF DIAGNOSTIC RESULTS (IGNITION ON)

In this mode, Diagnostic Trouble Codes (DTC's) can be retrieved from the ECM. The DTC is indicated by the flashing sequence from the MIL or the red LED on the ECM.

  1. Turn the ignition switch ON, but do not start the vehicle.
  2.  
  3. Turn the ECM diagnostic mode selector fully clockwise for two seconds, then turn it back fully counterclockwise.
  4.  
  5. Observe the red LED on the ECM or MIL light for stored codes.
  6.  

When the ignition is switched

OFFduring diagnostic modes, power to the ECM will drop after approximately five seconds. The ECM will automatically return to Mode I.

HEATED OXYGEN SENSOR MONITOR (ENGINE RUNNING)

In this mode the red LED on the ECM or MIL light will display the condition of the fuel mixture and whether the system is in closed loop or open loop. When the light flashes ON, the exhaust gas sensor is indicating a lean mixture. When the light stays OFF, the sensor is indicating a rich mixture. If the light remains ON or OFF, it is indicating an open loop system. If the system is equipped with two exhaust gas sensors, the left side will operate first.

  1. Turn the ignition switch ON.
  2.  
  3. Turn the diagnostic switch ON, by turning the switch fully clockwise for 2 seconds and then fully counterclockwise.
  4.  
  5. Start the engine and run it until it is thoroughly warm. Raise the idle to 2,000 rpm and hold for approximately two minutes. Confirm the red LED or MIL light flashes ON and OFF more than five times every ten seconds with the engine speed at 2,000 rpm.
  6.  

If equipped with two exhaust gas sensors, switch to the right sensor by turning the ECM mode selector fully clockwise for two seconds and then fully counterclockwise with the engine running.

 
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