DTC 45

DIAGNOSTIC CHART





WIRING DIAGRAM

INSPECTION PROCEDURE

Circuit Description:
The Engine 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 O2S 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(s) below refers to circled number(s) on the diagnostic chart.
1. DTC 45 is set when the O2S signal voltage or CKT D7.
- 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) but less than 25%.

Diagnostic Aids:
Using the "Scan Tool", observe the block learn values at different rpm conditions to determine when the DTC 45 may have been set. If the conditions for DTC 45 exists, 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 DTC 45 may be set. See "Fuel System Diagnosis".
- Leaking injector.
- 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.
- Evaporative Emission (EVAP) canister purge. Check for fuel saturation. If full of fuel, check canister control and hoses. See "EVAP Canister Purge" in "Evaporative Emission Control System".
- 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 rich condition is gone while the sensor is disconnected.
- Throttle Position (TP) Sensor. An intermittent TP Sensor output will cause the system to go rich, due to a false indication of the engine accelerating.