DTC 45

CIRCUIT DESCRIPTION
The Engine Control Module (ECM) supplies a voltage of about 0.45 volt between terminals "D7 and D6". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts.) The 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 sensor is like an open circuit and produces no voltage when it is below about 360°C (600°F) An open sensor circuit or cold sensor causes open loop operation.

Code 45 is set when the O2 sensor signal voltage at the ECM C-D connector terminal D-7
^ Remains above 0.7 volt for 30 seconds;
and
^ Engine time after start is 1 minute or more.

CHART TEST DESCRIPTION
1. Grounding the diagnostic terminal with the engine running, enables the "Field Service Mode" and allows the ECM to confirm either open or closed loop operation using the "CHECK ENGINE" light.

2. A steady light or "Open Loop" indicates the fault is present. Grounding CKT 412 causes a low O2 signal voltage. If the ECM and wiring are OK, The ECM should recognize the low voltage and confirm the lean signal by turning off the "CHECK ENGINE" light for at least 15 seconds.

3. Diagnostic aids:
^ 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 will reset. See diagnosis Chart A-7A. Chart A-7A Fuel System Diagnosis
^ Rich injector. Perform cylinder balance test Chart C-2A. Chart C-2A Injector Balance Test
^ Leaking injector. See Chart A-7A. Chart A-7A Fuel System Diagnosis
^ HEI Shielding. An open ground CKT 453 may result in EMI, or induced electrical "noise". The ECM looks at this noise as distributor 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 Chart C-3. Chart C-3 Canister Purge Check
^ MAF sensor. An output that causes the ECM to sense a higher than normal manifold pressure (low vacuum) can cause the system to go rich. Disconnecting the MAF sensor will allow the ECM to set a fixed value for the Mass Air Flow (MAF) sensor. Substitute a different MAF sensor if the the rich condition is gone while the MAF sensor is disconnected.
^ Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.
^ TPS. An intermittent TPS Output will cause the system to go rich, due to a false indication of the engine accelerating.
^ Inspect Oxygen 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 driveability problem.