Operation CHARM: Car repair manuals for everyone.

DTC 45

Code 45 Wiring Diagram:




Code 45 - Oxygen (O2) Sensor Circuit (Rich Exhaust Indicated):





CIRCUIT DESCRIPTION:
The 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 Oxygen (O2) 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° C (600° F). An open sensor circuit or cold sensor causes "Open Loop" operation.

TEST DESCRIPTION
Number below refers to circled number on the diagnostic chart.
1. Code 45 is set when:
- Oxygen (O2) sensor signal voltage greater than .700 volt for 50 seconds and in closed loop
- Throttle position is greater than 2% (about .2 volts above idle voltage) but less than 25%
- Engine time after start is more than 1 minute

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 exist, the block learn 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 Code 45 may be set. See "Fuel System Diagnosis" CHART A-7.
- Leaking injector
See CHART A-7.
- Check for fuel contaminated oil.
- HEI Shielding
An open ground CKT B3 (ignition system reference low) 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. See EMISSION CONTROLS.
- 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.
- TPS
An intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.