Rear Ho2S Signal
A functional test of the rear HO2S sensors is done during normal vehicle operation. The peak rich and lean voltages are continuously monitored. Voltages that exceed the calibratable rich and lean thresholds indicate a functional sensor. If the voltages have not exceeded the thresholds after a long period of vehicle operation, the air/fuel ratio may be forced rich or lean in an attempt to get the rear sensor to switch. This situation normally occurs only with a green catalyst (< 500 miles). If the sensor does not exceed the rich and lean peak thresholds, a malfunction is indicated.
2005 MY and beyond vehicles will continuously monitor the rear HO2S signal for high voltage, in excess of 1.1 volts and store a unique DTC (P0138, P0158). An over voltage condition is caused by a HO2S heater or battery power short to the HO2S signal line.
2011 MY and beyond vehicles with Conti-Moto CBP-A2 PCM will also continuously monitor the rear HO2S signal for out of range low voltage, below -0.2 volts and store DTC P2A01, P2A04. An out of range low voltage condition is caused by swapped sensor wires (sensor signal and signal return) and sensor degradation.
Furthermore, the rear HO2S signal will also be monitored continuously for circuit open or shorted to ground beginning 2011 MY as the PCM hardware becomes capable of measuring HO2S impedance. An intrusive circuit test is invoked whenever the HO2S voltage falls into a voltage fault band. A pull-up resistor is enabled to alter the HO2S circuit characteristics. A very high HO2S internal resistance, > 500 k ohms, will indicate an open HO2S circuit while a low HO2S internal resistance, < 10 ohms, will indicate a HO2S circuit shorted to ground. Both HO2S circuit open and shorted to ground malfunction will set DTC P0137, P0157 if the fault counter exceeds the threshold.
Beginning 2015MY, Conti ATIC142 UEGO ASIC has both UEGO and rear HO2S wire diagnostics capability included on the chip. The wire diagnostics will continuously detect sensor wires open, shorted to battery, or ground.
| DTCs Sensor 2 | P0136 - HO2S12 No activity or P2270 - HO2S12 Signal Stuck Lean P2271 - HO2S12 Signal Stuck Rich P0156 - HO2S22 No activity or P2272 - HO2S22 Signal Stuck Lean P2273 - HO2S22 Signal Stuck Rich |
| Monitor execution | once per driving cycle for activity test |
| Monitor Sequence | > 30 seconds time in lack of movement test (UEGO only), > 30 seconds time in lack of switch test, front HO2S/UEGO response test completed, Stream 2 HO2S circuit open/short to ground test time slice completed. |
| Sensors OK | ECT, IAT, MAF, MAP, VSS, TP, ETC, FRP, FVR, DPFE EGR, VCT, VMV/EVMV, CVS, CPV, EVAPSV, FTP, CKP, CMP, ignition coils, injectors, no misfire DTCs, no system failures affecting fuel, no EVAP gross leak failure, UEGO/HO2S (front and rear) heaters OK, no "lack of switching" malfunction, no "lack of movement" malfunction (UEGO only), no UEGO/HO2S (front and rear) circuit malfunction, no rear HO2S out of range low malfunction, no UEGO FAOS monitor malfunction, no front HO2S/UEGO response rate malfunction |
| Monitoring Duration | continuous until monitor completed |
| Entry Condition | Minimum | Maximum |
| Stream 1 HO2S not in CSD recovery mode | ||
| Flex Fuel Composition not changing | ||
| Not in Phase 0 of Evaporative System Monitor | ||
| No Purge System reset | ||
| Purge intrusive test not running | ||
| Not performing CSER spark retard | ||
| Engine Coolant Temp | 150 °F | 240 °F |
| Intake Air Temp | 140 °F | |
| Time since entering closed loop fuel | 10 seconds | |
| Inferred Catalyst Midbed Temperature | 1600 °F | |
| Heater-on Inferred Sensor(s) 2/3 HO2S Temperature Range | 400 °F | 1400 °F |
| Sensor(s) 2/3 HO2S heater-on time | 90 seconds | |
| Short Term Fuel Trim Range | -9% | 11% |
| Fuel Level (forced excursion only) | 15% | |
| Throttle position | Part throttle | |
| Engine RPM (forced excursion only) | 1000 rpm | 2000 rpm |
| UEGO ASIC not in recalibration mode | ||
| No air passing through during valve overlap (scavenging). | ||
| Battery Voltage | 11.0 Volts | 18.0 Volts |
| Does not exceed rich and lean threshold envelope: Rich < 0.42 volts Lean > 0.48 volts |
| Monitor ID | Test ID | Description | Unit |
| $02 | $01 | HO2S12 sensor switch-point voltage | volts |
| $06 | $01 | HO2S22 sensor switch-point voltage | volts |
| $03 | $01 | HO2S13 sensor switch-point voltage | volts |
| $07 | $01 | HO2S23 sensor switch-point voltage | volts |
| DTCs | P0138 - HO2S12 Circuit High Voltage P0158 - HO2S22 Circuit High Voltage |
| Monitor execution | continuous |
| Monitor Sequence | None |
| Sensors OK | rear HO2S heaters OK |
| Monitoring Duration | 10 seconds to register a malfunction |
| Entry Condition | Minimum | Maximum |
| Inferred Stream 2/3 HO2S Temperature | 400 °F | |
| Sensor(s) 2/3 HO2S heater-on time | 90 seconds | |
| Voltage at sensor 2 HO2S connector | 11.0 Volts | |
| Battery Voltage | 11.0 Volts | 18.0 Volts |
| > 1.1 volts for 10 seconds for over voltage test |
| DTCs | P2A01 HO2S12 Circuit Range/Performance (Bank 1 Sensor 2) P2A04 HO2S22 Circuit Range/Performance (Bank 2 Sensor 2) |
| Monitor execution | continuous |
| Monitor Sequence | None |
| Sensors OK | rear HO2S heaters OK, no rear HO2S shorted to ground malfunction |
| Monitoring Duration | 10 seconds to register a malfunction |
| Entry Condition | Minimum | Maximum |
| Inferred Stream 2 HO2S Temperature | 400 °F | |
| Sensor 2 HO2S heater-on time | 90 seconds | |
| Voltage at sensor 2 HO2S connector | 11.0 Volts | |
| Battery Voltage | 11.0 Volts | 18.0 Volts |
| < -0.2 volts for 10 seconds for out of range low test |
| DTCs | P0137 HO2S12 Circuit Low Voltage (Bank 1 Sensor 2) P0157 HO2S22 Circuit Low Voltage (Bank 2 Sensor 2) |
| Monitor Execution | Continuous |
| Monitor Sequence | None |
| Sensors OK | rear HO2S heaters OK, no rear HO2S out of range low malfunction, no rear HO2S functional DTCs |
| Monitoring Duration | 10 seconds to register a malfunction |
| Entry Condition | Minimum | Maximum |
| Closed Loop | ||
| Inferred Stream 2 HO2S Temperature | 680 °F | 1290 °F (short to ground) |
| Inferred Stream 2 HO2S Element Temperature (applicable only if Stream 2 HO2S Heater Impedance Monitor is enabled) | 480 °F | |
| Time Stream 2 HO2S inferred element temperature within 10% of the predicted steady state temperature (applicable only if Stream 2 HO2S Impedance Monitor is enabled) | 1 second | |
| Sensor 2 HO2S heater-on time | 60 seconds | |
| All injectors on (no Decel Fuel Shut Off) | ||
| Not commanding lean lambda due to torque reduction | ||
| Not requesting enrichment due to catalyst reactivation following decel fuel shut off | ||
| Sensor 2 HO2S voltage (open circuit voltage fault band): Conti-Moto CBP-A2 PCM Other PCMs or depending on feedback circuit |
-0.05 Volts 0.27 Volts 1.30 Volts |
0.05 Volts 0.50 Volts 1.90 Volts |
| Sensor 2 HO2S voltage (circuit shorted to ground voltage fault band) | -3.00 Volts | 0.06 Volts |
| Voltage at sensor 2 HO2S connector | 11.0 Volts | |
| Battery Voltage | 11.0 Volts | 18.0 Volts |
| HO2S Circuit Open: HO2S Impedance > 500 k ohms, fault counter > 14 (200 msec test every 500 msec check) HO2S Circuit Shorted to ground: HO2S Impedance < 10 ohms, fault counter > 17 (100 msec test every 500 msec check) |
| DTCs | P0137 - HO2S12 Circuit Low Voltage (Bank 1 Sensor 2) P0157 - HO2S22 Circuit Low Voltage (Bank 2 Sensor 2) P0138 - HO2S12 Circuit High Voltage P0158 - HO2S22 Circuit High Voltage |
| Monitor Execution | Continuous |
| Monitor Sequence | None |
| Sensors OK | HO2S heaters OK |
| Monitoring Duration | 10 seconds to register a malfunction |
| Entry Condition | Minimum | Maximum |
| Fault reported by UEGO ASIC | ||
| Battery Voltage | 11.0 Volts | 18.0 Volts |
| UEGO ASIC indicated malfunction, DTC sets after 10 seconds when circuit failure is present. |