Federal Emissions

Code 45 Diagnostic Chart:

Oxygen Sensor Circuit Diagram:

CIRCUIT DESCRIPTION
The ECM supplies a voltage of about .55 volt between terminals "A16" and "A22". (If measured with a 10 megohm digital voltmeter, this may read as low as .35 volt.) The Oxygen Sensor (02S) varies the voltage within a range of approximately 1 volt. If the exhaust is rich, the O2S will display near 1 volt and when the exhaust is lean, the O2S signal will display close to 100 mV.

The sensor is like an open circuit and produces no voltage when it is below about 315°C (600°F). An open 02S circuit or cold 02S causes "Open Loop" operation.

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

1. DTC 45 will set if:
^ Voltage on CKT 412 remains above .7 volt for 50 seconds.
^ Engine time after start is 1 minute or more.
^ Throttle angle between 3% and 45%.
^ Operation is in "Closed Loop."


DIAGNOSTIC AIDS:
Using the Tech 1 (or equivalent) scan tool, observe the long term fuel trim values at different RPM and air flow conditions. The Tech 1 (or equivalent) scan tool 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 exists, the long term fuel trim values will be around 115.

^ 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. Related Tests, Information and Procedures

^ Rich injector. Perform "Injector Balance Test," CHART C-2A.Chart C-2A Fuel Injector Balance Test

^ Leaking injector. Refer to CHART A-7.Related Tests, Information and Procedures

^ Check for fuel contaminated oil.

^ 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 O2S signal indication). The ECM will then reduce the amount of fuel delivered to the engine, causing a severe surge driveability problem.

^ Electronic ignition. An open ground CKT 453 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.

^ EVAP canister purge. Check for fuel saturation. If full of fuel, check canister control and hoses. Refer to "Evaporative Emission (EVAP) Control System".

^ 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 Oxygen Sensor (O2S) to indicate a rich O2S signal and this could result in a DTC 45.