Circuit Description

PCM continuously monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. During monitoring, PCM counts number of times sensor switches from rich to lean and from lean to rich, and adds amount of time required to complete all switches. Thus, an average time for all switches can be determined. If average time to switch is too slow, Code P0133 will set. A sensor that switches too slowly is most likely defective and should be replaced. Code P0133 will set when the following conditions are present.

• Engine is started.
• Intake air and engine coolant temperatures are less than 122°F (50°C).
• Intake air and engine coolant temperatures are within 11°F (6°C) of one another at start-up.
• TP sensor angle is between 2 and 10 percent for 100 seconds.
• Engine is operating in closed loop mode.
• Codes 14, 15, 18, 21, 22, 24, 26, 29, 33, 34, 36, 43, 47, 48, 50, 51, 53, 55, P0116, P0117, P0118, P0171, P0172, P0174, P0175, P1114 and P1115 are not set.
• All conditions are met, and average time for sensor to switch from lean to rich is longer than .1 second, or average time for sensor to switch from rich to lean is longer than .1 second.

A lean to rich switch is determined when sensor voltage changes from less than .3 volt to greater than .6 volt. A rich to lean switch is determined when sensor voltage changes from greater than .6 volt to less than .3 volt. Code P0133 will only fail on a cold start with ECT and IAT less than 122°F (50°C), and within 11°F (6°C) at start-up. If a condition for Code P0133 is present and ECT is greater than 122°F (50°C), PCM will not run Code P0133 test.