California Models

PURPOSE
The self-diagnostic system is designed to help technicians fix cars faster. This is done by having ECCS Control Module (ECM) monitor certain input/outputs and store a trouble code if the ECM detects a problem.

OPERATION
The self-diagnostic system has two modes. Mode 1 is the normal operating mode for the vehicle and will turn on the "MALFUNCTION INDICATOR LAMP" if a monitored system has a fault. Mode 2 is used for self diagnostics. Both modes do different things depending whether the engine is running or not.

Diagnostic Test Mode 1 - California Models:

Diagnostic trouble code No. Malfunction
12 Mass air flow sensor circuit
13 Engine coolant temperature sensor circuit
14 Vehicle speed sensor circuit
31 ECM (ECCS Control Module)
32 EGR function
33 Heated oxygen sensor circuit
35 EGR temperature circuit
43 Throttle position sensor circuit
45 Injector leak

Mode 1:
Key On Engine Off:
^ This is the "MALFUNCTION INDICATOR LAMP" self-check. If the lamp does not illuminate in this mode, check the electrical circuit.
Engine Running:
^ This is the normal operating mode. The "MALFUNCTION INDICATOR LAMP" will illuminate only if trouble is found in certain circuits.

DTC Example:

DTC Table:

Mode 2:
Key On Engine Off:
^ This is the stored codes self-diagnostic mode. Trouble codes will be extracted in this mode.
Engine Running:
^ When the engine is running it is used to monitor the air/fuel mixture and Oxygen Sensor operation.

HEATED OXYGEN SENSOR MONITOR

Heated Oxygen Sensor Test Table:

OPERATION
In this mode, the Malfunction Indicator Lamp and Red LED display the condition of the fuel mixture (lean or rich) which is monitored by the heated oxygen sensor.

Malfunction Lamp Operation:

HOW TO CHECK HEATED OXYGEN SENSOR
1. Set Diagnostic Test Mode II.
2. Start engine and warm it up until engine coolant temperature indicator points to the middle of the gauge.
3. Run engine at about 2,000 rpm for about 2 minutes under no-load conditions.
4. Make sure Red LED or Malfunction Indicator Lamp goes ON and OFF more than 5 times every 10 seconds; measured at 2,000 rpm under no-load.