EWMA Fault Filtering
The EWMA logic incorporates several important CARB requirements. These are:
- Fast Initial Response (FIR): The first 4 tests after a battery disconnect or code clear will process unfiltered data to quickly indicate a fault. The FIR will use a 2-trip MIL. This will help the service technician determine that a fault has been fixed.
- Step-change Logic (SCL): The logic will detect an abrupt change from a no-fault condition to a fault condition. The SCL will be active after the 4th DCMS monitor cycle and will also use a 2-trip MIL. This will illuminate the MIL when a fault is instantaneously induced.
- Normal EWMA (NORM): This is the normal mode of operation and uses an Exponentially Weighted Moving Average (EWMA) to filter the DCMS test data. It is employed after the 4th DCMS test and will illuminate a MIL during the drive cycle where the EWMA value exceeds the fault threshold. (1 trip MIL).
REAR O2 DFSO RESPONSE MONITOR OPERATION
| DTCs | P013A - O2 Sensor Slow Response - Rich to Lean (Bank 1 Sensor 2) P013C - O2 Sensor Slow Response - Rich to Lean (Bank 2 Sensor 2) P013E - O2 Sensor Delayed Response - Rich to Lean (Bank 1 Sensor 2) (sensor stuck in range) P014A - O2 Sensor Delayed Response - Rich to Lean (Bank 2 Sensor 2) (sensor stuck in range) |
| Monitor Execution | Once per driving cycle, after 3 DFSO events. |
| 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, HO2S 2 and 3 functional tests completed, HO2S/UEGO heater voltage and current checks completed, FAOS monitor system bias maturity met (UEGO applications only) |
| Sensors OK | ECT, IAT, MAF, VSS, TP, ETC, FRP, EGR, VCT, VMV/EVMV, CVS, FTP, CKP, CMP, ignition coils, injectors, no misfire DTCs, no system failures affecting fuel, no EVAP gross leak failure, UEGO heaters OK, rear HO2S heaters OK, no "lack of switching" malfunction, no "lack of movement" malfunction, no UEGO circuit malfunction, no rear stream 2 HO2S circuit malfunction, no rear stream 2 HO2S functional DTCs, Not performing CSER spark retard. Flex fuel composition not changing. No intrusive EGO monitors running. |
| Monitoring Duration | 3 DFSO events, 450 seconds on the FTP. |
TYPICAL DFSO RESPONSE MONITOR ENTRY CONDITIONS
| Entry Condition | Minimum | Maximum |
| Air Mass | 0.5 | 6 |
| Vehicle Speed | 90 | |
| Inlet Air Temp | 140 °F | |
| Engine Coolant Temp | 155 °F | 240 °F |
| Catalyst Temperature (Inferred) | 800 °F | 1600 °F |
| Rear Ego Tip Temperature (Inferred) | 800 °F | |
| Fuel Level | 15% | |
| Fuel In Control | -3% | 3% |
| Adaptive Fuel Within Limits | -3% | 3% |
| Battery Voltage | 11.0 Volts | 18.0 Volts |
| Rich Voltage on downstream CMS sensor(s) | 0.6 Volts | |
| Rich Voltage on upstream HEGO / UEGO sensor(s) | 0.45 Volts (HEGO) | 1 UEGO) |
TYPICAL DFSO RESPONSE RATE MALFUNCTION THRESHOLDS
| Rich to lean slew rate thresholds: Normal Threshold = > 0.0 mV/sec Fast Initial Response Threshold = > 0.0 mV/sec Step Change Threshold = > 0.3 mV/sec
NOTE:
Note that the thresholds use a normalized offset and the threshold is set at "zero".
|
TYPICAL DFSO DELAYED RESPONSE MALFUNCTION THRESHOLDS
| Successive failures are counted up (5 to 10 faults). Monitor will now intrusively force rich fuel to run the test. Intrusive controls will time out based on driveability (1 to 2 sec). Successive driveability failures are counted up (3 faults). Intrusive controls will now time out at a slower time (5 to 10 sec) and count a fault. After 3 faults are counted, a DTC is set. |
J1979 DFSO RESPONSE RATE MODE $06 DATA
| Monitor ID | Test ID | Description | Unit |
| $02 | $85 | HO2S12 Fuel Shut off Rich to Lean Response Rate (P013A) | mV/sec |
| $02 | $86 | HO2S12 Fuel Shut off Rich to Lean Response Time (P013E) | msec |
| $06 | $85 | HO2S22 Fuel Shut off Rich to Lean Response Rate (P013C) | mV/sec |
| $06 | $86 | HO2S22 Fuel Shut off Rich to Lean Response Time (P014A) | msec |