Threshold OVERBOOST Monitoring (2014)
The pressure-based overboost diagnostic is adequate for detecting a turbo stuck in the closed position on the dyno cert application, however with a stuck turbocharger on the chassis cert application the pressure deviation is not significant because of wastegate operation. With a wastegate in place, the closed loop boost pressure governor is capable of maintaining the desired boost pressure with the turbocharger stuck in a closed position. The functional overboost monitor is not able to detect this, so an additional boost system diagnostic is utilized since desired pressure is maintained in the system.v
The closed loop boost pressure controller controls boost based predicted control targets and anticipated turbocharger position. The output value, in percentage, indicates the "control effort" required to maintain the desired boost pressure. With a turbocharger stuck in the closed position, the control effort decreases. There is a temperature entry condition, torque entry conditions, a steady state requirement on manifold pressure, an exhaust temperature entry condition, and a threshold map. If the threshold is exceeded for 4 seconds, a fault is detected.
THRESHOLD OVERBOOST MONITOR
| DTCs |
P0234 - Turbocharger/Supercharger "A" Overboost Condition |
| Monitor Execution |
Continuous |
| Monitor Sequence |
None |
| Sensors OK |
ECT, MAP, MAF |
| Typical Monitoring Duration |
4 sec |
TYPICAL THRESHOLD OVERBOOST ENTRY CONDITIONS
| Entry Condition |
Minimum |
Maximum |
| Engine Torque |
200 Nm |
700 Nm |
| Engine Coolant Temperature |
-7 deg C |
|
| Ambient Air Temperature |
-7 deg C |
|
| Barometric Pressure |
75 kPa |
110 kPa |
| MAP Steady State Pressure |
|
100 kPa |
| TOxiCatUs Temperature |
99 deg C |
|
| Mass Air Flow |
|
1300 kg/h |
| Not in Cold Start Warm-up Mode |
|
| Regeneration Status |
None |
TYPICAL THRESHOLD OVERBOOST MONITOR MALFUNCTION THRESHOLDS
| If control effort percent is < threshold map for 4 seconds a fault is detected. |
TYPICAL THRESHOLD OVERBOOST MONITOR (P0234) THRESHOLD MAP
| RPM/TRQ |
600 |
750 |
1000 |
1200 |
1600 |
2000 |
2250 |
2500 |
2750 |
3000 |
3250 |
3500 |
| 0 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 100 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 150 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 200 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 250 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 300 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 350 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 400 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 450 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 500 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 600 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
| 700 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |
-43 |