Engine Controls - OBD II Overview
Classification: EF&EC94-006Section: Emission Control
Reference: TECHNICAL BULLETIN NTB94-051
Model: 1995 Maxima, 240SX
Date: May 9, 1994
1995 MAXIMA / 240SX POWERTRAIN
ON BOARD DIAGNOSTICS (OBD-II)
APPLIED MODELS:
All 1995 Maxima models
All 1995 240SX models
1995 Maxima and 240SX vehicles will be introduced with the next generation On Board Diagnostics system (OBD-II) for improved emission control. The level of diagnostics has been significantly increased for these models. This bulletin provides a brief overview of this system and includes vehicle handling procedures.
Operating Logic
The OBD-II system will store a Diagnostic Trouble Code (DTC) when a malfunction is detected in one of the monitored systems. Vehicle operating conditions (rpm, vehicle speed, etc.) at the time the malfunction occurs will also be stored, assisting the technician in duplicating and repairing the incident. CONSULT can be used to access this information from the OBD-II memory.
If the malfunction is detected on a second, consecutive driving "trip", the Check Engine light (Malfunction Indicator Lamp or "NUL") will illuminate. The MIL will illuminate on the first detection for a catalyst-damaging misfire or catalytic converter malfunction.
For most incidents, the MIL will stop illuminating if the incident no longer occurs, but the DTC and driving condition information will be stored in the OBD-II memory. This information is stored for 40 "trips" after the last malfunction (80 "trips" for catalyst-damaging malfunctions).
Complete information regarding the operation of the OBD-II system (including troubleshooting and repairing malfunctions in monitored systems) can be found in the Engine Control (EC) section of the applicable 1995 Service Manual.
Vehicle Handling Precautions
Connections and battery
^ Always ensure the ignition key is switched "OFF" before disconnecting or reconnecting the battery.
^ Always ensure the ignition key is switched "OFF" before disconnecting or reconnecting any OBD connections (engine or A/T electrical connections) and that the connections were securely reconnected before the key was switched "ON".
Repair Confirmation Procedure
Please complete the procedure below to evaluate an OBD-II (MIL) repair or if you suspect the ignition key was not switched "OFF" as specified above.
1) Turn ignition switch to "OFF".
2) Connect CONSULT to the data link connector (located behind the fuse box cover). Turn ignition switch to "ON".
3) Touch "START".
4) Touch "ENGINE". Touch "down arrow" key.
5) Touch "FREEZE FRAME DATA". Touch "PRINT". Touch "BACK" once.
6) Touch "SELF-DIAG RESULTS".
7) Touch "ERASE". (The DTCs in the Engine Control Unit will be erased).
8) Operate the vehicle under the conditions found under "FREEZE FRAME DATA". (A minimum of one minute of idling is required.)
9) Using CONSULT, reconfirm that no DTCs are stored.