DTC 45

Code Chart 45:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:
The ECM supplies a voltage of about .45 volt between terminals "GE14" and "GE15." (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The Oxygen Sensor (02S) varies the voltage within a range of about 1 volt, if the exhaust is rich, down through about .10 volt, if exhaust is lean.

The sensor produces no voltage when it is below about 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 02S signal voltage or CKT 412.

^ Remains above .7 volt for 50 seconds; and in "CLOSED LOOP."
^ Engine time after start is 1 minute or more.
^ Throttle angle between 3% and 45%.

DIAGNOSTIC AIDS:
Using the scan tool, observe the L.T. fuel trim values at different RPM and air flow conditions. The scan tool also displays the L.T. fuel trim cells, so the L.T. 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 L.T. 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. Related Tests, Information and Procedures
^ Rich Injector. Chart C-2A Fuel Injector Balance Test
^ Leaking injector. Related Tests, Information and Procedures
^ Check for fuel contaminated oil.

Check for:

^ Short to voltage on CKT 412.
^ HEI Shielding. An open ground CKT 453 (electronic ignition system) 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. See EVAP Canister Purge," in "Evaporative Emission Control System," in Emission Control Systems.
^ MAP Sensor. A shifted "High" MAP sensor could cause the fuel system to go rich.
^ 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 to indicate a rich exhaust.