The heated oxygen sensor (HO2S) bank 1 sensor 2 is threaded into the cylinder 1, 3, 5 exhaust pipe behind the pre-converter (cylinders 1, 3 and 5 are closest to the front of the dash). The sensor is an electrical source that responds to oxygen content out of the pre-converter. When the sensor reaches approximately 316°C (600°F), it produces a voltage based on the difference in oxygen between the atmosphere and exhaust gas. The ECM sends a bias voltage (421-479 mV) on the signal line, which is pulled up through high resistance. When the HO2S bank 1 sensor 2 is cold, it produces no voltage and has extremely high internal resistance. The internal resistance of the sensor is much greater than the resistance of the bias pull-up resistor. However, when the sensor heats up, it produces voltage that overrides the bias voltage. This voltage is read by the ECM to determine the efficiency of the catalytic converter. Under normal conditions, low sensor voltage means high oxygen content/lean air-fuel mixture and vice versa. Normal sensor readings at steady cruise with a properly functioning catalytic converter will be around 500-800 mV. If the ECM does not see the expected response (the signal switching above or below a threshold for a certain length of time) from the HO2S bank 1 sensor 2, the ECM will command a rich and lean status to force a response. DTC P0139 sets when the HO2S bank 1 sensor 2 does not react for a certain length of time.
DTC Parameters
DTC P0139 will set if HO2S bank 1 sensor 2 does not react to an ECM commanded rich or lean status when:
| • | The condition exists for longer than 1 minute and 40 seconds. |
| • | The HO2S bank 1 sensor 2 is in a closed loop. |
| • | The calculated converter temperature is less than 940° C (1724° F). |
| • | The battery voltage is greater than 11.0 volts. |
| • | The commanded air/fuel ratio is 14.7 to 1. |
DTC P0139 will set if the HO2S bank 1 sensor 2 voltage is greater than 200 mV in decel fuel cut-off mode for more than 5 seconds (2002 only).
DTC P0139 diagnostic runs continuously once the above conditions have been met.
P0139 is a type B DTC.
Diagnostic Aids
A leaking fuel injector on bank 1, cyl. 1, 3, or 5 can set this DTC (2002 only). A good indication of this would be fuel in the engine oil or a hard start condition. If either of these are suspect, perform a fuel rail leakdown test.
Important: An intermittent open in either signal wire will not set this DTC.
Important: Do not apply grease or any material in the HO2S bank 1 sensor 2 harness connector or alter the wiring in any way. The wires carry air reference to the sensor used to determine the difference in oxygen between the exhaust gas and atmosphere.
