DTC 45

Code Chart 45:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:
The Engine Control Module (ECM) supplies a voltage of about .45 volt between terminals "D10" and "D11." (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.)

When the Oxygen Sensor (O2S) reaches operating temperature, it varies this voltage from about .1 volt (exhaust is lean) to about .9 volt (exhaust is rich).

The sensor is like an open circuit and produces no voltage when it is below 316°C (600°F). An open sensor circuit, or cold sensor, causes "OPEN LOOP" operation.

TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 45 is set when the O2S signal voltage on CKT 412 remains above .7 (700 mV) volt under the following conditions:

^ Engine run time after start is 2 minutes or more.
^ System is operating in "CLOSED LOOP."
^ Throttle angle is greater than 5%.
^ Above conditions exist for 51 seconds or more.

DIAGNOSTIC AIDS:
Using the scan tool, observe the long term fuel trim value at different engine speeds. If the conditions for DTC 45 exist, the long term fuel trim values will be around 90 or lower.

Check the following possible causes:

^ 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 DTC 45 will be set. Related Tests, Information and Procedures
^ Leaking Fuel Injector - Related Tests, Information and Procedures
^ An open ground CKT 453 - May result in induced electrical "noise." The ECM interprets this "noise" as reference 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 evaporative emission vapor canister is full of fuel, check EVAP canister control valve and hoses. Refer to Emission Control Systems.
^ 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 Manifold Absolute Pressure (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.
^ TP Sensor - An intermittent Throttle Position (TP) sensor output will cause the system to operate richly due to a false indication of the engine accelerating.
^ O2S Contamination - Inspect Oxygen Sensor (O2S) 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 surge driveability problem.
^ EGR Valve - Exhaust Gas Recirculation (EGR) sticking open at idle is usually accompanied by a rough idle and/or stall condition.
^ If DTC 45 is intermittent, Testing and Inspection
^ Engine Oil Contamination - Fuel fouled engine oil could cause the O2S to sense a rich air/fuel mixture and set a DTC 45.