Code EO44, Lean Exhaust Indication: Notes

The ECM supplies a signal voltage of about .45 volt between terminals D7 and D6. (If measured with a 10 megaohm digital voltmeter, this may read as low as .32 volts.) The oxygen sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about .10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below about 600°F (360°C). An open sensor circuit or cold sensor causes "open loop" operation.

Code EO44 is set when oxygen sensor signal voltage at the ECM "C-D" connector terminal D7: Remains below 250 mv for 60 seconds or more and time since engine start is 1 minute or longer. The engine must be in "closed loop" mode for the above conditions. This does not cause the fuel integrator to reset to 128.

1. Entering "Diagnostic Mode" allows the ECM to confirm either "open" or "closed loop" operation. This also allows the oxygen sensor to be monitored.
2. A light out or "open loop" indicates the fault is present. Disconnecting the oxygen sensor will raise the signal voltage above .2 volt. If the ECM and wiring are okay, the ECM should recognize the higher voltage (.35-.55) and flash "open loop" when in the service diagnostic mode and the engine is started.