The time between HO2S switches is monitored after vehicle startup when closed loop fuel has been requested, during closed loop fuel conditions and when open loop fuel has been requested due to an HO2S fault. Excessive time between switches with short term fuel trim at its limits (up to +/- 40%), or no switches since startup indicate a malfunction. Since "lack of switching" malfunctions can be caused by HO2S sensor malfunctions or by shifts in the fuel system, DTCs are stored that provide additional information for the "lack of switching" malfunction. Different DTCs indicate whether the sensor was always indicates lean/disconnected (P2195, P2197), or always indicates rich (P2196, P2198).
Characteristic Shift Downward (CSD) is a deviation from the normal positive voltage output of the HO2S signal to negative voltage output. During a full CSD, the HO2S signal shifts downward (negative) by 1 volt. CSD occurs when the reference chamber of the HO2S becomes contaminated, causing negative HO2S voltage to be generated. Even though CSD can occur in both front and rear HO2S signals, only the front HO2S are compensated for CSD. The CSD compensation algorithm must not be in the process of driving fuel to bring the HO2S out of CSD before running some of the HO2S monitors.
2005 MY and later vehicles monitor the HO2S signal for high voltage, in excess of 1.1 volts and store a (P0132, P0152) DTC. An over voltage condition is caused by a HO2S heater or battery power short to the HO2S signal line.
HO2S "LACK OF SWITCHING" OPERATION:
| DTCs |
P2195 - Lack of switching, sensor indicates lean, Bank 1
P2196 - Lack of switching, sensor indicates rich, Bank 1
P2197 - Lack of switching, sensor indicates lean, Bank 2
P2198 - Lack of switching, sensor indicates rich, Bank 2 |
| Monitor execution |
continuous, from startup and while in closed loop fuel or open loop fuel due to HO2S fault |
| Monitor Sequence |
None |
| Sensors OK |
ECT, IAT, MAF, VSS, TP, ETC, FRP, DPFE EGR, VCT, VMV/EVMV, CVS, FTP, CKP, CMP, ignition coils, injectors, no misfire DTCs, no system failures affecting fuel, no EVAP gross leak failure, front HO2S heaters OK, no front HO2S over voltage |
| Monitoring Duration |
30 seconds to register a malfunction |
TYPICAL HO2S "LACK OF SWITCHING" ENTRY CONDITIONS:
| Entry Condition |
Minimum |
Maximum |
| Closed Loop or Open Loop Requested due to HO2S fault |
|
|
| Stream 1 HO2S not in CSD recovery mode |
|
|
| No fuel flow entering thru PCV during cold start when flashing off fuel in oil (for O2 Sensor Stuck Rich DTCs only |
|
|
| Inferred Ambient Temperature |
-40 °F |
|
| Time within entry conditions |
10 seconds |
|
| Fuel Tank Pressure |
|
10 in H2
O |
| Fuel Level |
15% |
|
| Battery Voltage |
11.0 volts |
18.0 volts |
TYPICAL HO2S "LACK OF SWITCHING" MALFUNCTION THRESHOLDS:
| < 5 switches since startup for > 30 seconds in test conditions or > 30 seconds since last switch while closed loop fuel |
HO2S "OVER VOLTAGE TEST" OPERATION:
| DTCs |
P0132 - O2 Sensor Circuit Higher Voltage, Bank 1
P0152 - O2 Sensor Circuit Higher Voltage, Bank 2 |
| Monitor execution |
Continuous |
| Monitor Sequence |
None |
| Sensors OK |
front HO2S heaters OK |
| Monitoring Duration |
10 seconds to register a malfunction |
TYPICAL HO2S "OVER VOLTAGE TEST" ENTRY CONDITIONS:
| Entry Condition |
Minimum |
Maximum |
| Inferred Stream 1 HO2S temperature |
400 °F |
|
| Battery Voltage |
11.0 volts |
18.0 volts |
TYPICAL HO2S "OVER VOLTAGE TEST" MALFUNCTION THRESHOLDS:
| HO2S Voltage > 1.1 volts for 10 seconds for over voltage test |
The HO2S is also tested functionally. The response rate is evaluated by entering a special 1.5 Hz. square wave, fuel control routine. This routine drives the air/fuel ratio around stoichiometry at a calibratable frequency and magnitude, producing predictable oxygen sensor signal amplitude. A slow sensor will show reduced amplitude. Oxygen sensor signal amplitude below a minimum threshold indicates a slow sensor malfunction. (P0133 Bank 1, P0153 Bank 2). If the calibrated frequency was not obtained while running the test because of excessive purge vapors, etc., the test will be run again until the correct frequency is obtained.
HO2S RESPONSE RATE OPERATION:
| DTCs |
P0133 - O2 Sensor Circuit Slow Response Bank 1
P0153 - O2 Sensor Circuit Slow Response Bank 2 |
| Monitor Execution |
once per driving cycle |
| Monitor Sequence |
> 30 seconds time in lack of switch test |
| Sensor OK |
ECT, IAT, MAF, VSS, TP, ETC, FRP, DPFE EGR, VCT, VMV/EVMV, CVS, FTP, CKP, CMP, ignition coils, injectors, no misfire DTCs, no system failures affecting fuel system, no EVAP gross leak failure, no "lack of switching" malfunctions, front HO2S heaters OK no front HO2S over voltage |
| Monitoring Duration |
6 seconds |
TYPICAL HO2S RESPONSE RATE ENTRY CONDITIONS:
| 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 |
| Fuel Level |
15% |
|
| Short Term Fuel Trim Range |
-9% |
11% |
| Short Term Fuel Trim Absolute Change while in monitor |
|
10% |
| Engine Load |
20% |
50% |
| Maximum change in engine load while in monitor |
|
0.13 |
| Vehicle Speed |
30 mph |
80 mph |
| Maximum change in vehicle speed while in monitor |
|
3 mph |
| Engine RPM |
1000 rpm |
2000 rpm |
| Maximum change in engine rpm while in monitor |
|
150 rpm |
| Battery Voltage |
11.0 volts |
18.0 volts |
TYPICAL HO2S RESPONSE RATE MALFUNCTION THRESHOLDS:
| Voltage amplitude: < 0.5 volts |
J1979 FRONT HO2S MODE $06 DATA
| Monitor ID |
Test ID |
Description |
Units |
| $01 |
$80 |
HO2S11 voltage amplitude and voltage threshold (P0133/P0153) |
Volts |
| $01 |
$01 |
H02S11 sensor switch-point voltage |
Volts |
| $05 |
$80 |
HO2S21 voltage amplitude and voltage threshold (P0133/P0153) |
Volts |
| $05 |
$01 |
H02S21 sensor switch-point voltage |
Volts |