ECU trouble codes and diagnosis from Haynes Manual for Nissan Pickups 1980-1996 and Pathfinders 1987-1995. Below I have copied the step by step info on how to run the self diagnosis and other tests on the models listed above.  Hope all of this helps and you understand the Haynes Lingo. Self Diagnosis Procedure
		To access the code information on the 1996 models it is necesary for you to use a GST(generic scan tool), or the CONSULT scan tool and support test equipment.  (Whatever that means.  Glad I have a 91 model HB).  These tools are very expensive and are not recommended for use by the home mechanic.  The flashing green and red LED's are no longer used on these models (96 and up).  If you suspect a problem with the emissions related components, have the system checked by a dealer service department or other repair shop. The self diagnosis is useful to diagnose malfunctions in major sensors and actuators of the ECCS system.  There are five modes in the self diagnosis system. 1.  Mode I Exhaust gas sensor monitor - During a closed loop condition (when the engine is warm), the the green inspection lamp turns ON indicating a lean condition, or OFF to indicate a lean condition.  During an open loop condition(when the engine is cold), the grean lamp remains ON or OFF. 2.  Mode II Mixture ration feedback control monitor - During closed loop operation, the red inspection lamp turns ON or OFF simultaneously with the green inspection lamp when the mixture ratio is controlled within the specified value.  During the open loop condition, the red lamp remains ON or OFF. 3.  Mode III Self diagnosis - The mode stores all of malfunctioning diagnostic items in it's memory.  It will be stored in the memory until the starter is operated 50 times, or until the power of the ECU is interupted.  This is the most useful of the modes.  I will list all of the trouble codes for this mode below, or on another page.  I am not sure yet.  You will be able to find them.  4.  Mode IV  Switches ON/OFF diagnosis - During this mode, the inspection lamp monitors the idle switch portion of the throttle valve switch, the starter switch, vehicle speed sensor and the other switches with an ON/OFF condition 5.  Mode V  Real time diagnosis - The moment the malfunction is detected, the display will be represented.  The is the mode in which the malfunction can be observed during a road test as it occurs.  (Although I don't know how you are going to see the ECU when you are driving.  I think that you will have a little more problems than you 02 sensor when you are driving with you head under the passenger seat.  Maybe some people are more talented than I am).                               Switching the modes 1990-1995 models with the MPFI system      Turn the ignition switch to the ON position.  Turn the diagnostic mode selector on the ECU fully clockwise and wait until the inspection lamps flash.  Count the number of flashes to find which mode you are in, then when you get to the mode that you want, turn the mode selector fully counterclockwise.        When the ignition switch is turned to the off position during diagnosis, and turned on again, in each mode, and the power of the ECU has dropped off completely, the diagnosis will automatically return to Mode I.       The Check Engine light on the instrument panel (CA models only) comes on when the ignition switch is turned on or in Mode I when the emmisions system malfunctions (with the engine running).       Malfunctions related to fuel and emmisions control systems can be can be diagnosed using the self diagnostic codes of Mode III.        To start the diagnostic procedure remove the ECU from under the passenger seat. Start the engine and warm it up to normal operating temperature.  Turn the dianostic mode selector on the ECU fully clockwise.  After the inspection lamps have flashed 3 times turn the diagnostic mode selector fully counterclockwise.  The ECU is now in Mode III.  Check the trouble code chart below for the particular malfunction.        After the tests have been performed and the repairs completed, erase the memory by turning the diagnostic mode selector on the ECU fully clockwise.  After the inspection lamps have flased 4 times, turn the mode selector fully counterclockwise.  This will erase any signals the ECU stored concerning a particular component.                        Self-Diagnosis System Trouble Codes (Mode III) Code 11                                                             Crank angle sensor circuit (1 red flash, 1 green flash  Code 12                                                             Air flow meter/circuit (1 red flash, 2 green flashes)                          Code 13                                                             Engine temperature sensor (1 red flash, 3 green flashes)                Code 14                                                             Vehicle speed sensor (1 red flash, 4 green flashes) Code 21                                                              Ignition sensor (2 red flashes, 1 green flash) Code 31                                                              Ecu contro unit (3 red flashes, 1 green flash) Code 32                                                              EGR function (3 red flashes, 2 green flashes) Code 33                                                              Exhaust gas sensor (3 red flashes, 3 green flashes) Code 34                                                              Detonation sensor (3 red flashes, 4 green flashes) Code 35                                                              Exhaust gas temperature sensor (3 red flashes, 5 green flashes) Code 41                                                              Air temperature sensor (4 red flashes, 1 green flash)   Code 43                                                            Throttle sensor (4 red flashed, 3 green flashes)                                                                                           PAGE 2                                                                                                                              Back to main page