VCM (Manual Transmission)

DTC 45 (VCM):

HO2S Circuit (VCM):

Circuit Description:
The VCM supplies a voltage of about .45 volt between terminals "A9" and "A7". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The Oxygen Sensor (02S) 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 315°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 45 is set when the Oxygen Sensor (02S) signal (02S) voltage on CKT 412:
- Remains above .7 volt for 70 seconds and in "Closed Loop."
- Engine time after start is 1 minute or more.
- Throttle angle greater than 5% (about .2 volt above idle voltage).

Diagnostic Aids:
Using the Tech 1, observe the long term fuel trim values at different RPM and air flow conditions to determine when DTC 45 may have been set. If the conditions for DTC 45 exists, the long term fuel trim values will be around 115.
An oxygen supply inside the 02S is necessary for proper 02S operation. This supply of oxygen is supplied through the 02S wires. All 02S wires and connections should be inspected for breaks or contamination that could prevent reference oxygen from reaching the 02S.

- Fuel Pressure - System will go rich if pressure is too high. The VCM can compensate for some increase. However, if it gets too high, a Code 45 may be set.Related Tests, Information and Procedures

- Check for fuel contaminated oil.

- HEI Shielding - An open ground CKT 453 (ignition system reference low) may result in EMI, or induced electrical "noise." The VCM looks at this "noise" as reference pulses. The additional pulses result in a higher than actual engine speed signal. The VCM 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.

- MAP Sensor - An output that causes the VCM to sensor a higher than normal manifold pressure (low vacuum) can cause the system to go rich Disconnecting the MAP sensor will allow the VCM to set a fixed value for the MAP sensor. Substitute a different MAP sensor if the rich condition is gone while the sensor is disconnected.

- Pressure Regulator - Check for leaking fuel pressure regulator diaphragm by checking for presence of liquid fuel.

- TP Sensor - An intermittent TP sensor output will cause the system to go rich, due to a false indication of the engine accelerating.

- ECT - Check for a shifted sensor that could cause a rich exhaust but set Code 15. Related Tests, Information and Procedures