DTC 45

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

Wiring Diagram for Open Oxygen Sensor Circuit.:

CODE 45 - OXYGEN SENSOR CIRCUIT (RICH EXHAUST INDICATED)


Circuit Description:


The Electronic Control Module (ECM) supplies a voltage of about .45 volt between terminals "D6" and "D7". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The 02 sensor 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 is like an open circuit and produces no voltage when it is below about 360 degrees C (600 degrees 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 is set when the O2 sensor 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 greater than 2% (about .2 volt above idle voltage)


Diagnostic Aids:

Using the "Scan", observe the block learn values at different rpm conditions 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. Check:

-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 may be set. See "Fuel System Diagnosis" CHART A-7.

-For Rich Injector
Perform injector balance test CHART C-2A.

-For Leaking Injector
See CHART A-7.

-For fuel contaminated oil.


-High Energy Ignition (HEI) Shielding
An open ground CKT 453 (ignition system reflow) may result in Electro Magnetic Interference (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.

-Manifold Absolute Pressure (MAP) Sensor
An output that causes the ECM to sense a lower than normal vacuum can cause the system to go rich. Disconnecting the MAP sensor will allow the ECM to set a fixed value for the sensor. Substitute a different MAP sensor if the the rich condition is gone while the sensor is disconnected. Check for leaking fuel pressure regulator diaphram by checking vacuum line to regulator for fuel.

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