1) Turn ignition switch to ON position. Use a screwdriver to turn ECM diagnostic mode selector fully clockwise.
2) Wait for inspection lights to begin flashing. At this
time, inspection lights will flash mode options (i.e., one flash for Mode I, 2 flashes for Mode II, etc.). As soon as inspection light flashes desired mode number (3 flashes for self-diagnostic mode), turn mode selector off (fully counterclockwise)
3) If mode selector is kept in ON position (fully clockwise), mode selections will continuously cycle. This cycling will not erase memory.
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NOTE: Not all trouble codes will activate MIL (CHECK ENGINE light)
Trouble codes are read using Red LED and Green LED inspection lights on side of ECM. After selecting Mode III, trouble codes corresponding to mode will start flashing. Trouble codes are indicated by number of flashes from ECM Red LED and Green LED inspection lights. Count number of flashes. Red LED indicates first digit of code, and Green LED indicates second digit of code. For example, 3 flashes of Red LED followed by 2 flashes of Green LED indicate Code 32.
Self-diagnostic system can be operated in any of 5 modes. Modes are manually changed using screwdriver through access port of ECM. With screwdriver turned fully clockwise, inspection lights will begin to flash. Count number of flashes. First flash is Mode I, second flash is
Mode II, etc. When desired mode has been indicated, turn screwdriver fully counterclockwise. In different modes, Red LED and Green LED perform different functions.
Mode I (Exhaust Gas Monitor)
This is normal vehicle operating mode. Green LED will indicate loop status. If Green LED is not blinking, vehicle is in open loop or a fault exists with oxygen sensor or sensor circuit. If Green LED is blinking, vehicle is in closed loop. If a malfunction occurs in Mode I, Red LED and MIL (CHECK ENGINE light) will illuminate, indicating an engine control system malfunction has occurred.
Mode II (Mixture Ratio Feedback Monitor)
In Mode II, both Red LED and Green LED are used to monitor air/fuel mixture feedback control. Green LED will function as in Mode I. In open loop, Red LED and Green LED will remain on or off. For results to be valid, vehicle must be in closed loop. In closed loop, Red LED will indicate if system is running rich (light off), lean (light on) or at ideal air/fuel ratio (blinking synchronized with Green LED)
Mode III (Self Diagnostics)
When Mode III is accessed, codes stored in ECM memory will be flashed by Green LED and Red LED on side of ECM. Red LED will flash first digit of code, while Green LED will flash second digit of code. For example: 3 flashes of Red LED followed by 5 flashes of Green LED indicate a Code 35.
Mode IV (Switch Check)
This mode is used for checking engine control systems switch status. When idle switch or starter switch is activated, Red LED will come on and go off as status changes. For vehicle speed sensor status, Green LED will remain off when vehicle speed is less than 12 MPH and
come on when vehicle speed is greater than 12 MPH.
Mode V (Test Mode)
Mode V represents a real-time diagnostic test of camshaft position sensor, ignition signal and mass airflow output signal. This mode is accessed for an in-bay running test of vehicle. Red and Green LED5 must be monitored carefully during this test, with special attention paid to number of flashes before each pause. Malfunction code will be displayed only once and will not be stored in memory. If Red LED blinks on and off evenly, a fault exists in camshaft position sensor. If Green LED flashes twice before a pause, a fault exists in airflow meter. If Green LED blinks 4 times before a pause, a fault exists in ignition signal.
|Without Onboard Diagnostics (OBD-II)|
|11||Camshaft position sensor.|
|12||Mass airflow (MAF) sensor.|
|13||Engine coolant temperature (ECT) sensor..|
|14||Vehicle speed (VSS) sensor.|
|21||No ignition referance.|
|23||Throttle Valve Switch|
|31||Engine control module (ECM).- A/C, light,fan and PS switch|
|32||EGR sensor.- starter switch|
|34||Knock (detonation) sensor (3.0 L).|
|35||EGR temp sensor.|
|41||Air temp sensor.|
|43||Throttle position sensor (TPS).|
|51||Injector circuit (3.0 L).|
|55||No malfunction recorded.|