With Speed Density Update

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

Wiring Diagram for Oxygen Sensor Circuit.:

CIRCUIT DESCRIPTION
The Electronic Control Module (ECM) supplies a voltage of about 0.45 volt between terminals "A16" and "A22". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt.) The Oxygen (O2) Sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.10 volt if exhaust is lean. The O2 sensor is like an open circuit and produces no voltage when it is below about 315° C (6OO° F). An open sensor circuit or cold sensor causes "Open Loop" operation.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Code 45 will set if:
^ The voltage on circuit 412 remains above 0.7 volt for 30 seconds.
^ The engine has been running for 1 minute or more.
^ The throttle angle between 3% and 45%.
^ Operation is in "Closed Loop."

DIAGNOSTIC AIDS
Using the "SCAN" tool, observe the block learn values at different RPM and air flow conditions. The "SCAN" tool 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.

Fuel Pressure / Leaking Injector
System will go rich if pressure is too high and/or the injector(s) is leaking. The ECM can compensate for some increase. However, if it gets too high, a Code 45 may be set. Refer to Diagnostic Charts / Chart A4-7. Chart A4-7 Fuel System Diagnosis

Rich Injector
Perform "Injector Balance Test", refer to Diagnostic Charts / Chart C-2A. Chart C-2A Injector Balance Test

Sensor Contamination
Inspect the O2 sensor 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.

High Energy Ignition (HEI) Shielding
An open ground circuit 453 (ignition system reflow) 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.

Canister Purge
Check for fuel saturation. If full of fuel, check canister control and hoses. Refer to Diagnostic Charts / Chart C-3. Chart C-3 Canister Purge Check

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

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

Exhaust Gas Recirculation (EGR)
An EGR staying open (especially at idle) will cause the O2 sensor to indicate a rich exhaust, and this could result in a Code 45.