Monitoring Procedure (Heater)
HEATED OXYGEN SENSOR (HO2S) - HEATERDiagnostic Codes:
P1185/P1186, P1187/P1188, P1189/P1190,
P1191/P1192, P1193/P1194, P1195/P1196
Monitoring Procedure
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.
Fig. 1 Upstream Sensors:
Fig. 2 Downstream Sensors:
Location
The Heated Oxygen Sensors (HO2S) are situated before and after the catalysts in the exhaust system and are identified as follows:
Bank 1 - Cylinders 1 to 3 - forward exhaust system
Bank 2 - Cylinders 4 to 6 - rearward exhaust system
Sensor 1 - Sensor upstream of the catalyst - close to the cylinder head
Sensor 2 - Sensor downstream of the catalyst - away from the cylinder head
NOTE: HO2S sensors and harness connectors are not identified as to position, so when sensors, harness or exhaust are changed they must be label led to enable correct reconnection and location. Failure to observe this precaution may require the use of a Jaguar Diagnostic equipment to re-programme the ECM.
Fig. 2 HO2S Circuit:
Description
The HO2S resistance varies with temperature and so a heater is used to maintain a constant tip temperature of approximately 700 °C. At this temperature the sensor output will be 3.3 V for lean running and 1.1 V for rich running.
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.