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Old 01-20-2009, 10:59 PM
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Default P1133

O2 Sensor, Insufficient Switching.

I was able to get this code off of my PCM. What does this mean? I replaced my post-cat sensor and the code has since gone away (SES light went out).. however, what does this code mean? I've never heard of Insufficient Switching before. And a search on the forum didn't turn up the info I wanted to learn.
95 Chevy Blazer LT 4WD, 177k
Old 01-21-2009, 07:19 AM
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Default RE: P1133

P1133 - HO2S Insufficient Switching Bank 1 Sensor 1

Basically, the PCM monitors the voltage from the O2 sensor. The O2 sensor puts out a varying voltage between 100mV and 900mV (typically) depending on the oxygen content of the exhaust. As the PCM changes IPWs (injector pulse widths) in response to data from all of the engine sensors, the O2 sensor detects these changes and sends the corresponding signal to the PCM. If the PCM does not detect the changes (cross counts or transitions past the preset bias voltage) that it knows it should be detecting, it sets this code.

Here is an excerpt from the DTC diagnostic listing:
The Heated Oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. It also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean-out" the mixture, when the HO2S detects a rich exhaust condition.

Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor catalyst efficiency.

This Diagnostic Trouble Code (DTC) determines if the HO2S is functioning properly. It checks for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV . This DTC sets when the Vehicle Control Module (VCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are:[*]An open or a short to voltage on either the HO2S signal or HO2S low circuits[*]A malfunctioning HO2S[*]A problem in the HO2S heater or its circuit[*]A faulty HO2S ground
Old 01-21-2009, 07:19 AM
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97, 99, blazer, chevy, code, detecting, h02s, insufficient, o3, p1133, pcm, sensor, switching, trouble, voltage

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