Heated Oxygen Sensors (HO2S) - Heater

Diagnostic Codes:
P1185/P1186, P1187/P1188, P1189/P1190,
P1191/P1192, P1193/P1194, P1195/P1196

The heaters are connected to the ECM in pairs and hardware detection will provide indication of both heaters in a pair open circuit or, one or both heaters short circuit. The heater current and average output tests use the closed loop tip temperature control system to indicate faults and, if this system is unable to control tip temperature satisfactorily, then a number of faults can be detected.

If a fault is registered, the system will default to operating the heaters whenever the fuel pump is on, except when engine speed and load are above limits.

The strategy will report to the Diagnostic Status Manager (DSM) when an oxygen sensor heater fault is present and the DSM will then decide whether to store a fault code and illuminate the MIL lamp.


Sensor Heater Open Circuit
HO2S Sensor Heater Open Circuit - Banks land 2 Sensor 1, P1185
HO2S Sensor Heater Open Circuit - Banks land 2 Sensor 2, P1191

Possible causes:
- Heater wiring open circuit
- ECM to heater connector open circuit
- ECM to heater wiring is short circuit to ground
- Both heaters open circuit supply - harness or connector faults
- Both heaters open circuit-sensor
- ECM hardware monitor fault implying open circuit heaters

Sensor Heater Short Circuit
HO2S Sensor Heater Short Circuit - Banks land 2 Sensor 1, P1186
HO2S Sensor Heater Short Circuit - Banks land 2 Sensor 2, P1192

NOTE: The heaters are connected to the ECM; hardware detection will provide indication of both heaters open circuit and one or both heaters short circuit.

Possible causes:
- ECM to heater wiring is short circuit to voltage source
- Both heaters short circuit - sensor
- ECM hardware monitor fault implying short circuit heaters

Sensor Heater Open Circuit
HO2S Sensor Heater Open Circuit - Inferred - Banks 1 and 2 Sensor 1, P1187
HO2S Sensor Heater Open Circuit - Inferred - Banks 1 and 2 Sensor 2, P1193

NOTE: The heaters are connected to the ECM in pairs; hardware detection will provide indication of both heaters open circuit and one or both heaters short circuit.

Possible causes:
- Heater harness high resistance or open circuit
- Excessive ignition retard causing hot exhaust gases
- Both heaters high resistance
- Incorrect test timing - air flow meter problem
- Incorrect heater calibration - ECM programming
- ECM fault - heater control system

Sensor Heater - Resistance
HO2S Sensor Heater - Resistance - Banks 1 and 2 Sensor 1, P1188
HO2S Sensor Heater - Resistance - Banks 1 and 2 Sensor 2, P1194

The heater current and average output tests use the closed loop tip temperature control system to indicate faults. If the closed loop system is unable to control tip temperature then faults will be detected.

Possible causes:
- ECM to heater wiring is open circuit
- ECM to heater wiring is part open circuit
- ECM to heater wiring is short circuit to ground
- Battery voltage low and battery voltage sensing
- Both heaters are high resistance or open circuit - sensor
- ECM heater current monitor reads low
- Incorrect heater calibration
- ECM current sense resistor

Sensor Heater Circuit Low Resistance
HO2S Sensor Heater Circuit Low Resistance - 1 - Banks 1 and 2 Sensor 1, P1189
HO2S Sensor Heater Circuit Low Resistance - 1 - Banks I and 2 Sensor 2, P1195

The heater current and average output tests use the closed loop tip temperature control system to indicate faults. If the closed loop system is unable to control tip temperature then faults will be detected.

Possible causes:
- HC2S out of exhaust
- Heater harness short circuit
- Low battery voltage
- Incorrect test timing - air flow meter problem
- HO2S heater low resistance
- Incorrect heater calibration - ECM programming



Sensor Heater Circuit Low Resistance
HO2S Sensor Heater Circuit Low Resistance -2- Banks 1 and 2 Sensor 1, P1190
HO2S Sensor Heater Circuit Low Resistance -2- Banks 1 and 2 Sensor 2, P1196

The heater current and average output tests use the closed loop tip temperature control system to indicate faults. If the closed loop system is unable to control tip temperature then faults will be detected.

Possible causes:
- ECM to heater wiring short circuit to a voltage source
- Excess heater current - battery voltage > 17 V
- Both heaters low resistance or short circuit
- ECM heater current monitor reads high - CM fault
- Incorrect heater calibration - ECM programming
- ECM current sense resistor

Fig. 1 Sensor Resistance With Respect To Temperature:

Fig.2:

Additional Information
Figure above shows a graph of sensor resistance with respect to the tip temperature; GEMS controls the temperature of the tip to 700 °C.

The voltage level for any temperature may be calculated by taking the following readings and substituting them into the formula. Figure above shows the test points.