Circuit Description
The heated oxygen sensor (HO2S) bank 2 sensor 2 is threaded into the front exhaust pipe directly behind the cylinder 2, 4, 6 pre-converter. Cylinders 2, 4, 6 are closest to the radiator. The sensor is used by the engine control module (ECM) to determine the oxygen storage capability of the pre-converter, fuel trim biasing, time held lean or rich, and certain techniques used to diagnose DTCs associated with the pre-catalyst oxygen sensor. The sensor is equipped with a heater to provide additional heat to speed up sensor activation time. The ECM calculates the efficiency of the sensor heating element by calculating the internal sensor, NOT HEATER, resistance based on actual current and signal voltage measurements on circuit 1671 after the engine has been running a certain length of time. As temperature increases, the sensor internal resistance will decrease. The ECM compares modeled sensor resistance values to the measured values based on the calculated sensor temperature, exhaust gas temperature. If the heater is working properly, the internal sensor resistance will decrease at a certain rate based on the exhaust gas temperature. Normal internal sensor resistance values will vary between 80-250 ohms when the sensor is fully operational. If the resistance takes too long to decrease or is too high after a certain amount of engine run time, the heater is assumed to be heating insufficiently. DTC P0161 will set if the calculated internal sensor resistance is too high after a certain length of engine run time indicating an inefficient heating element.
Conditions for Setting the DTC
DTC P0161 will set if the HO2S bank 2 sensor 2 calculated sensor resistance, based on the actual signal voltage and actual signal current, is greater than 3,968 ohms when:
| • | The condition exists for longer than 15 seconds. |
| • | The engine is running. |
| • | The calculated converter temperature is between 400-580°C (752-1076 °F). |
| • | The battery voltage is between 7.5-15 volts. |
| • | No HO2S bank 2 sensor 2 heater circuit DTCs have been set. |
DTC P0161 diagnostic runs continuously once the above conditions have been met.
DTC P0161 is a type B DTC.
Diagnostic Aids
If DTC P0160 is also set, diagnose that DTC first. An open in the sensor signal or sensor return may set this DTC.
Make sure no corrosion is present in the HO2S bank 2 sensor 2 harness connector and that all terminals, heater AND signal, are contacting correctly. If OK, replace the HO2S bank 2 sensor 2.
The heater element resistance is 5-12 ohms.
