California Models
INSPECTION PROCEDURE FOR DTC 21NOTE: If DTC 21 is output inspect / replace front oxygen sensor.
If DTC 28 is output, inspect / replace rear oxygen sensor.
1. CHECK VOLTAGE BETWEEN TERMINALS HT1, HT2 OF ENGINE CONTROL MODULE (ECM) CONNECTOR AND BODY GROUND.
- Connect the check Harness A.
- Measure voltage between terminals HT1, HT2 of ECM connector and body ground.
Voltage: 9.0 - 14.0 volts
^ If OK proceed to step 3.
^ If not OK proceed to step 2.
2. CHECK MAIN HEATED OXYGEN SENSOR HEATER.
- Disconnect main heated oxygen sensor connector.
- Measure resistance between terminals 1 and 2 of main heated oxygen sensor connector.
OK if: Resistance....
@ 20°C (68°F)....11.7 - 14.3 ohms
^ If OK check and repair harness or connector between main relay and main heated oxygen sensor, main heated oxygen sensor and ECM.
^ If not OK replace main heated oxygen sensor.
3. CHECK VOLTAGE BETWEEN TERMINALS HT1, HT2 OF ENGINE CONTROL MODULE CONNECTOR AND BODY GROUND.
- Warm up engine to normal operating temperature.
- Measure voltage between terminals HT1, HT2 of ECM connector and body ground, when engine is idling and racing at 4,000 rpm.
Voltage idling....... 0.0 volts
Voltage @ 4,000 rpm... 9.0 - 14.0 volts
NOTE: In the 4,000 rpm racing check, continue engine racing at 4,000 rpm for approx. 20 seconds or more before testing.
^ If OK replace main heated oxygen sensor. [1]
^ If not OK check and replace ECM.
[1] It is probable the oxygen sensor has deteriorated. Usually, this cannot be confirmed by visual inspection.
INSPECTION USING OSCILLOSCOPE
