Secondary Air Monitor

Stage I runs when the Secondary Air Solenoid is on (Upstream Air Added). The Secondary Air Solenoid is switched on, or goes from blocked to upstream air under the following conditions:

Secondary Air Solenoid on Times:
1. Engine Running.
2. Coolant Temp after Start-Up below 120°F ECT = 2:00 minimum, above 120°F ECT = 0:20 minimum.
In Decel and all following items met:
1. Engine Temp above 0°F.
2. Engine Temp below 154°F.
3. MAP above 19" vacuum.
4. RPM above 1220 RPM.
5. RPM below 3500 RPM.

The PCM begins Stage I: The PCM monitors the Downstream O2S while the Secondary Air Solenoid is on (in the Upstream mode). If Downstream O2S is below .725 volts, the PCM goes to Step A. If Downstream O2S is above .745 volts, the PCM goes to Step B.

A. If the Downstream O2S is less than .725 volts, the PCM waits for the Secondary Air to be turned off. After the Secondary Air is turned off, the PCM monitors the Downstream O2S for 2 Seconds. If the Downstream O2S voltage is now above .745 volts, Stage I Passes and all testing is stopped this trip. If it is not above .745 volts, Stage I fails and Stage II begins.

B. If the Downstream O2S is greater than .745 volts with the Secondary Air Solenoid on (Upstream Air Mode), then the PCM fails Stage I and Stage II begins. The PCM begins Stage II after the following:

Stage I Failed.
Fuel System in Closed Loop.
At Idle.
Test not already failed this Trip.
RPM above 700 RPM.

In Stage II, the PCM richens the mixture until the Downstream O2S switches rich by doing the following:

The PCM changes the Upstream O2S rich switch point from .490 volts to 1.02 volts.
The PCM increments a counter by 0.02 volts every 2 seconds.
The PCM stops updating Long Term Adaptive Memory.
The PCM turns off the purge solenoid (No Purge Flow).
The PCM uses the Purge Free Idle Cell value for fuel calculations.
The PCM modifies the Fuel Ramps of Short Term Adaptive Memory.

If the Downstream O2S does not switch to rich (above .745 volts) before the Upstream O2S counter gets to 1.12 volts, the PCM fails Stage II and the Secondary Air Monitor fails 1 trip and Freeze Frame Data is stored.

If the Downstream O2S switches to rich (above .745 volts) before the Upstream O2S counter gets to 1.196 volts, the PCM turns the Secondary Air Solenoid on (Upstream Air Mode). The PCM resets Short Term Adaptive Memory to -1.5% and begins reducing the Short Term Adaptive Memory by -0.39% every 0.430 seconds until the Upstream O2S is below .859 volts.

Once the Upstream O2S is below .859 volts, the PCM holds the Short term Adaptive Memory at its present value. The PCM checks to see if the Downstream O2S has switched below .725 volts. If so, the PCM Passes Stage II and no further Testing is done this Trip. If the Downstream O2S has not switched below .725 volts, wait a maximum of 20 Seconds. If either 20 Seconds passes or the Downstream O2S has not switched below .725 volts, the PCM fails Stage II and the Secondary Air Monitor fails 1 trip and Freeze Frame Data is stored.