DTC 45

The ECM supplies a voltage of about 0.45 volts between terminals M2-23 and M2-22. (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts.) The O2 sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about .10 volts if the exhaust is lean.

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

Code 45 is set when the O2 sensor signal voltage at the ECM connector terminal M2-22 remains above 0.6 volts for 120 seconds.

1. 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 "Check engine" light.
2. A steady light or "Open loop" indicates the fault is present. Grounding CKT 31 causes a low O2 signal voltage. If the ECM and wiring are OK, the ECM should recognize the low voltage and confirm the lean signal by turning off the "Check engine" light for at least 30 seconds.
3. The Code 44 is most likely caused by one of the following:

^ Fuel Pressure. System will go rich if pressure is too high. The ECM can compensate for some increase. However, if it gets too high, a Code 45 will be set.
^ Leaking injector. See Fuel System Diagnosis chart.
^ HEI Shielding. An open ground CKT 16 may result in EMI, or indicated electrical "noise". The ECM looks at this "noise" as distributor pulses. The additional pulses result in a higher than actual engine speed signal. The ECM then delivers too much fuel, causing the system to go rich. The engine tachometer will also show higher than actual engine speed, which can help in diagnosing this problem.
^ Canister purge. Check for fuel saturation. If full of fuel, check canister control and hoses. See canister purge. Evaporative Emissions System
^ MAP sensor. An output that causes the ECM to sense a higher than normal manifold pressure (low vacuum) can cause the system to go rich. Disconnecting the MAP sensor will allow the ECM to set a fixed value for the MAP sensor. Substitute a different MAP sensor if the rich condition is gone while the sensor is disconnected.
^ Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.
^ TPS. An intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.
^ Inspect Oxygen Sensor for silicone contamination from fuel, or use of improper RTV sealant. The sensor may have a white, powdery coating and result in a high but false signal voltage (rich exhaust indication). The ECM will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.