DTC 45

Chart - Code 45 Oxygen Sensor Circuit, Rich Exhaust Indication:

Wiring Diagram for Oxygen Sensor Circuit:

CODE 45 - OXYGEN SENSOR CIRCUIT (RICH EXHAUST INDICATED)


Circuit Description:
The Electronic Control Module (ECM) supplies a voltage of about .45 volts (450 mV) between terminals "D6" and "D7". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volts). The 02 sensor varies the voltage within a range of about 1 volt (1000 mV) if the exhaust is rich, down through about .10 volts (100 mV) if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below about 360"C (600 degrees F) An open sensor circuit or cold sensor causes "Open Loop" operation.

Test Description:Code 45 is set when the 02 sensor signal voltage or CKT 412 Remains above .7 volt for 3O seconds in "Closed Loop", Throttle angle between 3% and 45% and Engine has been running 1 minute or more.


Diagnostic Aids:

Using the "Scan", observe the block learn values at different rpm and air flow conditions. The "Scan" also displays the block cells, so the block learn values can be checked in each of the cells to determine when the Code 45 may have been set. If the conditions for Code 45 exists, the block learn values will be around 115.
Also Check:

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 may be set. See CHART A-7 "Fuel System Diagnosis".

Rich injector. Perform injector balance test CHART C-2A.

Leaking iniector. See CHART A-7.

Check for fuel contaminated oil.

HEI Shielding. An open ground CKT 453 (ignition system low reference signal) may result in EMI, or induced electrical "noise". The ECM looks at 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 system to go rich. Engine tachometer will also show higher than actual engine speed, which can help in diagnosing this problem.


Check Canister purge for fuel saturation. If full of fuel, check canister control and hoses.

A MAF sensor output that causes the ECM to sense a higher than normal airflow can cause the system to go rich. Disconnecting the MAF sensor will allow the ECM to set a fixed value for the sensor. Substitute a different MAF sensor if the the rich condition is gone while the sensor is disconnected or use tool J-36101 and test MAF Sensor.

Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

An intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.

An EGR staying open (especially at idle) will cause the 02 Sensor to indicate a rich exhaust, and this could result in a Code 45.