DTC 45

DTC 45 Chart Oxygen Sensor Circuit:

Oxygen Sensor Circuit Wiring Diagram:

Circuit Description:

The ECM supplies a voltage of about 450 mV between terminals "D6" and "D16". (If measured with a 10 megohm digital voltmeter, this may read as low as 320 mV.) The oxygen sensor varies the voltage within a range of about 1000 mV if a rich O2 Sensor signal is indicated, down through about 10 mV if a lean O2 Sensor signal is indicated.

The sensor is like an open circuit and produces no voltage when it is below 315°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 will set if:

^ Signal voltage remains above 700 mV for 50 seconds.
^ Throttle angle is greater than 4%.
^ System is operating in "Closed Loop."

Diagnostic Aids:


Using the scanner, observe long term fuel trim values at different RPM and load conditions. The scanner also displays the fuel trim cells, so the long term fuel trim values can be checked in each of the cells to determine when the DTC 45 may have been set. If the conditions for DTC 45 exist, the long term fuel trim values will be near 108.

^ 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 may be set. Refer to "Fuel System Diagnosis," CHART A-7.

^ Rich Injector. Perform "Injector Balance Test." CHART C-2A.

^ Leaking Injector. Refer to Fuel System Diagnosis," CHART A-7

^ Check for fuel contaminated oil.

^ EVAP Canister Purge. Check for fuel saturation. If full of fuel, check canister control and hoses. Refer to Evaporative Emission (EVAP) Control System, "Chart C-3".

^ MAP Sensor. An output that causes the ECM to sense a lower than normal vacuum can cause the system to go rich. Disconnecting the MAP sensor will allow the ECM to set a fixed value for the sensor. Substitute 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.

^ TP Sensor. An intermittent TP sensor output will cause the system to go rich, due to a false indication of the engine accelerating.

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