DTC 45

Oxygen Sensor Circuit Diagram:

CIRCUIT DESCRIPTION
The PCM applies a voltage of about 0.55 volt between circuits 412 and 413 (if measured with a 10 megohm digital voltmeter, this may read as low as 0.35 volt).the oxygen sensor varies this voltage within the range of 0.1 - 0.9 volt, depending on the oxygen content of the exhaust. The sensor is like an open circuit when cold (below approx. 315°C/600°F). An open sensor circuit or cold sensor causes the system to operate in "OPEN LOOP".

Code 45 will set when:
^ System is operating in closed loop.
^ Voltage in circuit 412 remains above 0.7 volt for 1 minute of more.
^ Engine run time after start-up is 1 minute or more.
^ TPS indicates throttle opening between 3% and 45%.
TEST DESCRIPTION

Code 45 Diagnostic Chart:

Numbers below refer to circled numbers on diagnostic chart.
1. After running engine as described, system should be in "CLOSED LOOP" and oxygen sensor signal should be varying between 0.3 and 0.6 volt (300 - 600 millivolts.)

DIAGNOSTIC AIDS
Using a "SCAN" tool, check the "Block Learn" values at different engine speeds and air flow conditions.
"SCAN" tool that reads "Block Cells" should be used. "Block Learn" values for each cell can be checked to help determine when the Code 45 may have been set. If conditions for Code 45 exist, "Block Learn" values will be around 115.

Also check the following:

^ Fuel Pressure - Engine will run rich if fuel pressure is excessive, even though computer may be commanding system to go lean. Computer may be able to compensate for slightly increased fuel pressure by commanding system "lean", but if engine is extremely rich, lean system command may not be enough and Code 45 will set. For fuel system pressure check, Related Tests, Information and Procedures

^ Injectors - Leaking injectors can cause a rich condition and set a Code 45. Perform injector balance test. Chart C-2A Fuel Injector Balance Test

^ Check for fuel contaminated engine oil.

^ Oxygen Sensor contamination - Inspect oxygen sensor for silicone contamination from fuel, or use of improper RTV type sealant. The sensor may have a white, powdery coating, and may be procuding a false rich indication. If this is the case, the PCM will command the system "Lean", resulting in severe driveability problems, surging, and possible backfiring if the condition is serious enough.

^ HEI Shielding - An open ground circuit 453 may cause electro-magnetic interference, or induced "Noise" in the ignition reference signal. The PCM may interpret this "Noise" as additional reference pulses and mis-calculate the engine speed as higher than actual. The PCM then would deliver too much fuel, causing the engine to run rich. If equipped with a tachometer, compare tach reading with engine speed reading on "SCAN" tool. If tach reading is lower than "SCAN" reading, this is a likely cause.

^ Evaporative Emission Control System - Check for fuel saturation of the charcoal canister. Also check canister purge solenoid valve and evaporative system hoses, fuel filler cap, etc. Chart C-3 Canister Purge Check

^ Throttle Position Sensor - Check TPS output. An intermittent problem with the TPS may create a false throttle angle indication, causing the base injector pulse width to be too great.

^ EGR - If the EGR is recirculating too much exhaust for the engine speed and load (especially if the EGR valve is open or leaking at idle), this will create a false rich exhaust indication.