DTC 45

CODE 45 OXYGEN SENSOR (O2S) CIRCUIT (RICH INDICATION)

Code Chart 45:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:

The ECM supplies a voltage of about 0.45 volt between terminals "D7" and "D6" of the ECM. (If measured with a 10 Meg ohm 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 to about 0.10 volt, if exhaust is lean. The sensor is like an open circuit and produces no voltage, when it is below about 360°C (600°F). An open sensor circuit, or cold sensor, causes "OPEN LOOP" operation.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 45 is set, when the 02 sensor signal voltage is fixed above 0.75 (750 mV) and the following:

^ TPS greater than 3%.
^ System operating in "CLOSED LOOP."
^ No Code 21 or 33.
^ Integrator not at 128.
^ Temperature above 69.5°C (155°F).

DIAGNOSTIC AIDS:

The Code 45, or rich exhaust, 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. Related Tests, Information and Procedures
^ HEI Shielding - An open ground YEL/BLK wire may result in EMI, or induced electrical "noise." The ECM looks at this "noise" as reference pulses. These additional pulses result in a higher than actual engine speed signal. The ECM then delivers too much fuel, causing system to go rich. 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 EMISSION CONTROL DEVICES.
^ 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.
^ TPS - An intermittent TPS output will cause the system to go rich, due to a false indication that the engine is accelerating.
^ 02 Sensor Contamination - Inspect Oxygen Sensor for silicone contamination from fuel or use of improper RTV sealant. The sensor may have a WHITE, powdery coating resulting 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 surge and driveability problem. If Code 45 is intermittent, Testing and Inspection
^ EGR - Valve sticking open at idle, usually accompanied by a rough idle, stall complaint.
^ If the O2 sensor heater fails, a Code 45 or Code 44 may set. To diagnose the heater part of the O2 sensor, Chart C-1F Oxygen Sensor Heater Check