Oxygen Sensor: Testing and Inspection

DIGIFANT II

Oxygen Sensor System - Checking

Requirements

- Engine oil temperature must be at least 80°C (176°F) and radiator cooling fan must come on at least once.
- Idle speed, timing, and CO content OK.
- The exhaust system between catalytic converter and cylinder head is not leaking
- The voltage supply for oxygen sensor heater is OK.
- The coolant temperature sensor and oxygen sensor connected.
- All electrical consumers switched OFF and radiator cooling fan must not be running during checking or adjusting.
- Remove the cap from the CO tap tube.



- Connect EPA 105 CO tester (or EPA approved equivalent) to CO tap tube using only special tool 6006-0019 or equivalent (non-approved hoses may dramatically alter the readings).
- Start the engine and raise speed to a minimum of 2100 RPM four times, letting the throttle close each time.
- This clears the fault memory in the E.C.U. and cancels the hot-start idle increase function.
- Check CO and record reading.
- Remove the oil fill cap from valve cover and observe CO reading.
- CO content must drop briefly and then increase to original value.

Note: If the CO content does not drop, there is a vacuum leak in the system.

If CO content does return to original value:

- Oxygen sensor system is OK and compensating properly.
- Re-install oil filler cap.

If CO content does not return to original value:

- Switch engine OFF and re-install oil filler cap.
- Disconnect oxygen sensor at 3-way connector.




Note: Some early vehicles are not equipped with a 3 pin lambda connector. On these vehicles, disconnect only the oxygen sensor connection (Arrow).

- Start the engine and raise speed to a minimum of 2100 RPM four times, letting the throttle close each time.



- Connect jumper wire lead to the terminal for the green wire which goes to the Digifant E.C.U. (Arrow).

Note: On 3 pin connector, connect jumper to terminal 1 in the white hard-shell (black wire).

- Hold jumper wire briefly to ground.
- CO content must rise. If CO content rises:
- Replace the oxygen sensor.

If CO content does not rise:

- Check for broken or grounded wire between oxygen sensor connector and terminal 2 of the E.C.U. connector.

If the wiring is OK:

- Replace the Digifant E.C.U.