UEGO Heaters
The UEGO heater is controlled as a function of the measured impedance to keep the sensor at a near constant temperature (Bosch: 780 deg C, NTK: 830 deg C). The impedance of the Nernst cell decreases as the sensor temperature increases. This impedance is measured by periodically applying a small current across the Nernst cell and measuring the change in the voltage. The output voltage is then sent to an A/D input on the PCM. After a cold start, the UEGO heater ramps up to the maximum duty cycle to heat the sensor. After a few seconds, the measured impedance will start to decrease and when the target value is crossed, the heater goes into closed loop heater control to maintain the sensor at a near constant temperature.
The "UEGO Heater Temperature Control Monitor" tracks the time at the maximum duty cycle during the open loop sensor warm up phase. If the measured impedance does not come down to the target value to allow the system to transition from open loop heater control to closed loop heater control within a specified time, then a P0030/P0050 fault code is set. This monitor also sets a malfunction when the closed loop heater controller reaches a maximum or minimum duty cycle for a period of time indicating that the controller is no longer able to maintain the target temperature. However, if the exhaust temperature is high enough that the sensor will be above the target temperature even with no heat, then this monitor is disabled.
The UEGO heaters are also monitored for proper voltage and current. A UEGO heater voltage fault (open, shorted to ground, or shorted to battery) is determined by turning the heater on and off and looking for corresponding voltage change in the heater output driver circuit in the PCM.
A separate current-monitoring circuit monitors heater current once per driving cycle. This monitor normally runs in closed loop heater control after all the exhaust gas sensor functional tests are completed (2010 MY and earlier), however, it can also run intrusively. When the UEGO sensor indicates cold, but the heater is inferred to have been adequately warm, the current monitor is forced to run intrusively prior to the completion of the heater temperature control monitor. If the heater measured current falls below or above a calibratable threshold, the heater is assumed to be degraded or malfunctioning.
Beginning 2012MY, some PCMs do not have a separate current-monitoring circuit. For PCMs that do not have the current-monitoring circuit, a degraded or malfunctioning UEGO heater is detected by the "UEGO Heater Temperature Control Monitor".
| DTCs | P0030
- HO2S Heater Control Circuit Bank 1 P0050 - HO2S Heater Control Circuit Bank 2 P0135 - HO2S Heater Circuit, Bank 1 P0155 - HO2S Heater Circuit, Bank 2 P0053 - HO2S Heater Resistance, Bank 1 P0059 - HO2S Heater Resistance, Bank 2 |
| Monitor execution | once per driving cycle for heater current monitor, continuous for voltage monitoring and UEGO heater temperature control monitoring |
| Monitor Sequence | Heater current monitor:
Stream 1 UEGO response test completed (2010 MY and earlier), Stream 2 and 3 HO2S functional tests completed (2010 MY and earlier), Stream 1 UEGO heater voltage check completed. UEGO heater temperature control monitor: Stream 1 UEGO heater voltage check completed, Stream 1 UEGO circuit check completed, intrusive heater current monitor completed (if applicable). |
| Sensors OK | Heater current monitor:
no HO2S/UEGO heater circuit malfunction, no UEGO heater temperature control malfunction, no UEGO circuit malfunction UEGO heater temperature control monitor: no UEGO circuit malfunction, no UEGO heater circuit malfunction, no UEGO heater current monitor DTCs. |
| Monitoring Duration | < 10 seconds for heater voltage check, < 5 seconds for heater current check, >= 30 seconds for the UEGO heater temperature control monitor to register a malfunction |
| Entry Condition | Minimum | Maximum |
| Inferred UEGO unheated tip temperature (heater voltage check only) | 75 °F | 1562 °F |
| Inferred UEGO heated tip temperature (heater current check only) | 1346 °F | 1526 °F |
| UEGO heater-on time (heater current check only) | 30 seconds | |
| Engine RPM (heater current check only) | 5000 rpm | |
| Time heater control voltage at maximum limit during open loop heater control (intrusive heater current check only | 9 seconds (Bosch UEGO) 20 seconds (NTK UEGO) |
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| Time heater control voltage at maximum or minimum limit during closed loop heater control (intrusive heater current check only) | 7 seconds (Bosch UEGO) 1 second (NTK UEGO) |
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| Inferred UEGO unheated tip temperature (heater control monitor only) | 75 °F | 1000 °F |
| UEGO ASIC not in recalibration mode | ||
| Battery Voltage | 11.0 Volts | 18.0 Volts |
| Monitor ID | Test ID | Description | Units |
| $41 | $81 | HO2S11 Heater Current (P0053) | Amps |
| $45 | $81 | HO2S21 Heater Current (P0059) | Amps |
