Code 44 - Lean Exhaust Indication
The ECM supplies approximately .45 volt between terminals "D6" and "D7". (This may read as low as .32 volt, if measured with a 10 megohm digital voltmeter). The O2 sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down to about .10 volt if the exhaust is lean. The O2 sensor is like an open circuit and produces no voltage when it is below about 315°C (600°F). An open sensor circuit or cold sensor causes open loop operation. Code 44 is set when the O2 sensor signal voltage at the ECM terminal "D7" remains below .2 volt for 20 seconds or more and the system is in closed loop.
NOTE:
The following step numbers refer to the numbers on the Diagnostic Flow Charts.
- Grounding the diagnostic terminal with the engine running enables the "Field Service Mode" and allows the ECM to confirm either open or closed loop operation using the "SERVICE ENGINE SOON" light.
- A light out or "open loop" indicates the presence of a fault. Disconnecting the O2 sensor will raise the signal voltage above .2 volt. If the ECM and wiring are okay, the ECM should recognize the higher voltage, .35 to .55 volt, and flash open loop when the engine is started.
- Check the following if Code 44 is set: MAF and O2 sensors, fuel contamination, EGR, low fuel pressure, lean injectors and exhaust leaks ahead of O2 sensors.