DTC 45

Heated Oxygen Sensor (HO2S) Circuit (Rich Heated Oxygen Sensor (HO2S) Signal Indicated):

Diagnostic Chart





Circuit Diagram

Circuit Description
The engine control module supplies a voltage of about 0.45 volts between terminals "83" and "82". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts.) The heated oxygen sensor varies the voltage within a range of about 1 volt, if the exhaust is rich, down through about 0.10 volts, 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, can cause "Open Loop" operation.

Test Description
The number(s) below refer to circled number(s) on the diagnostic chart.
1. Diagnostic trouble code 45 is set, when the heated oxygen sensor signal voltage is fixed above 0.1 volts (100 mV) under the following conditions:
- Throttle position sensor greater than 9.8%.
- No diagnostic trouble code 21A / 21B or 33A / 33B.
- The engine is running for longer than 180 seconds.
- System is operating in "Closed Loop".
- O2 Signal Voltage is less than 0.347 volts and greater than 0.547 volts.
- Temperature is above 69.5°C (155°F).
- Integrator not at 128.
- All of the above condition present for 50 seconds.

Diagnostic Aids
The diagnostic trouble code 45, or rich heated oxygen sensor signal, is most likely caused by one of the following:
- Fuel pressure: System will go rich, if pressure is too high. The engine control module can compensate for some increase. However, if it gets too high, a diagnostic trouble code 45 will be set.
- HEI shielding: An open ground CKT BLK/GRN may result in EMI, or induced electrical "noise". The engine control module looks at this "noise" as reference pulses. The additional pulses result in a higher than actual engine speed signal. The engine control module 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.
- Evaporate emission canister purge: Check for fuel saturation. If full of fuel, check canister control and hoses.
- Manifold absolute pressure sensor: An output that causes the engine control module to sense a higher than normal manifold absolute pressure (low vacuum) can cause the system to go rich. Disconnecting the manifold absolute pressure sensor will allow the engine control module to set a fixed value for the manifold absolute pressure sensor. Substitute a different manifold absolute pressure sensor, if the rich condition is gone, while the sensor is disconnected.
- Throttle position sensor: An intermittent throttle position sensor output will cause the system to go rich, due to a false indication of the engine accelerating.
- Heated oxygen sensor contamination: Inspect heated 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 heated oxygen sensor signal indication). The engine control module will then reduce the amount of fuel delivered to the engine, causing a severe surge driveability problem.
- Exhaust gas recirculation: valve sticking open at idle, usually accompanied by a rough idle, or stall complaint, especially at idle.