Circuit Description

The main oxygen sensor mounted in exhaust manifold monitors exhaust gas oxygen content and delivers an input signal to ECM. The ECM uses input signal to determine fuel injection system operation. Code is set when main oxygen sensor signal voltage is reduced to .35-.70 volt for 60 seconds under the following conditions:

• Engine coolant temperature is 176°F (80°C) or greater.
• Engine speed of 1500 RPM or greater.
• Driving under load, A/C on, flat surface at 50 MPH or greater.
• Manifold mounted oxygen sensor signal voltage is alternating above and below .45 volt.