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swartlkk -> P0155 Explained (3/20/2008 7:10:27 PM)
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P0155 - Heated Oxygen Sensor Heater Circuit (bank 2, sensor 1)
Schematic
[img]http://i11.photobucket.com/albums/a187/swartlkk/2000%20Bravada/th_P0155_SC.gif[/img]
CIRCUIT DESCRIPTION
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 convener 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
This DTC determines if the HO2S heater circuit is functioning properly by monitoring the amount of time required for the HO2S to reach operating temperature. This DTC sets when the VCM fails to detect HO2S voltage transitions above and below the bias range within a specified amount of time. Possible cause of this DTC are listed below.
* An open circuit in either the HO2S ignition positive or the HO2S heater ground circuits
* An HO2S heater element problem
CONDITIONS FOR RUNNING THE DTC
IMPORTANT: This test is void for this cold start if the system voltage remains outside the specified range for more than 4 seconds .
* The system voltage is between 11.7-18 volts .
* The MAF is less than 27 g/s .
* The engine run time is more than 2 seconds .
* The ECT is less than 33°C (91°F) .
* The IAT is less than 33°C (91°F) .
* The difference between the ECT sensor and the IAT sensor is no more than 5°C (9°F) .
CONDITIONS FOR SETTING THE DTC
The O2 sensor voltage remains within 150 mV of its startup voltage for 130 seconds after cold start.
ACTION TAKEN WHEN THE DTC SETS
* The control module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
* The co
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