P0134

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 thee HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module 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 the catalyst efficiency.

This Diagnostic Trouble Code (DTC) determines if the HO2S is functioning properly. The DTC also checks for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the Powertrain Control Module (PCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0128, P0200, P0300, P0351-P0358, P0401, P0404, P0405, P0410, P0418, P0443, P0446, P0449, P1120, P1220, P1221, P1258, or P1404 are not set.
^ The Secondary Air Injection (AIR) and the Exhaust Gas Recirculation (EGR) diagnostics are not active.
^ The ignition voltage is more than 9 volts.
^ The engine run time is more than 409 seconds.

CONDITIONS FOR SETTING THE DTC
The HO2S signal voltage is steady between 350-550 mV for 60 seconds or more.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
^ Inspect the following components and systems:
- An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or for contamination. Refer to Heated Oxygen Sensor (HO2S) Wiring Repairs in Diagrams.
- A loose HO2S causes this DTC to set.
^ Use the Freeze Frame/Failure Records data in order to locate an intermittent condition in the following ways:
- If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in determining how many miles since the DTC set.
- The Fail Counter and Pass Counter can also aid in determining how many ignition cycles the diagnostic reported a pass or a fail.
- Operate the vehicle within the same Freeze Frame conditions that you observed in order to isolate when the DTC failed. Use the following conditions for your tests:
^ The RPM
^ The load
^ The vehicle speed
^ The temperature
^ For an intermittent condition, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-7:

Steps 8-14:

Steps 15-22:

The numbers below refer to the step numbers on the diagnostic table.
2. After the HO2S heater is commanded ON, the HO2S heater heats up causing the HO2S signal voltage to either increase or decrease. This indicates that the HO2S heater is OK.
6. If the test lamp illuminates, the low reference circuit between the HO2S and PCM terminal C1-63 is OK and the PCM low reference terminal is OK.
7. If the voltage is below the specified value, the high signal circuit, the low reference circuit, and the PCM are OK.
11. The opposite bank HO2S must be disconnected to isolate a short to ground in the HO2S heater high control circuit.
15. Resistance within the specified range indicates the HO2S heater is OK.