Field Service Mode Check
- This test confirms proper operation of fuel system and verifies Closed Loop operation. Clear codes and perform this test after any repair is completed.
- When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on front-wheel drive models does not hold drive wheels.
- On some engines, the oxygen sensor will cool off after only a short period of time while engine is idling. This will cause engine to go into open loop. To restore closed loop mode, run engine at part throttle several minutes and accelerate from idle to part throttle several times. See Fig 1 .
NOTE:
Although there are many charts connected with CCC diagnosis, only 2 charts are needed to prove the system is operating properly. Normally, only 3 charts are necessary to find a problem, if one exists.
NOTE:
Open Loop at idle only may be caused by a cold oxygen sensor after a period of idling. If this is the cause, running engine at 2000-3000 RPM for one minute should warm it up and give closed loop operation at idle.