UNDERBOOST Monitoring

The underboost monitor works in a similar fashion to the overboost monitor by comparing the desired vs. actual measured boost pressure while in a specific range of closed loop boost pressure operation. If the boost pressure governor deviation is greater than the calibrated threshold for 7 seconds, a fault is detected and the P-code is set. The closed loop monitoring window is defined as any inner torque above 50 Nm, and any engine speed above 1500 rpm. The threshold limit is wider for the underbooost monitor due to transient boost system response, compensation for boost pressure lag, and short term (1-2 second) momentary torque truncation when air path torque is kept high, but fueling is limited for component protection.

This diagnostic will detect a gross air path leak such as the turbo discharge or CAC discharge tube being blown off, major pre-turbo exhaust leaks, or a turbo slowly responding or stuck in the open VGT position.

UNDERBOOST MONITOR

DTCs	P1247 - Turbocharger Boost Pressure Low P0299 - Turbocharger/Supercharger "A" Underboost Condition P259E - Turbocharger "A" Boost Control Position At Low Limit
Monitor Execution	Continuous
Monitor Sequence	None
Sensors OK	ECT, MAP, MAF, VGTP
Typical Monitoring Duration	7 sec

TYPICAL OVERBOOST MONITOR ENTRY CONDITIONS

Entry Condition	Minimum	Maximum
Closed-Loop Boost Control	enabled
P1247:
Engine Torque	50 Nm
Engine Speed	1000 rpm	4000 rpm
P259E:
Engine Torque	50 Nm
Engine Speed	1000 rpm	4000 rpm
P0299:
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 UNDERBOOST MONITOR MALFUNCTION THRESHOLDS

P1247: If desired boost pressure - actual boost pressure > 15 kPa
P0299: If control effort percent > threshold (see map below) for 4 seconds and exhaust lambda <1.33
P259E: If desired VGT position - actual VGT position < -25%

TYPICAL THRESHOLD UNDERBOOST MONITOR (P0299) THRESHOLD MAP

RPM/TRQ	600	750	1000	1200	1600	2000	2250	2500	2750	3000	3520	3500
0	50	50	50	50	50	50	50	50	50	50	50	50
100	50	50	50	50	50	50	50	50	50	50	50	50
150	50	50	50	50	50	50	50	50	50	50	50	50
200	50	50	20	12	12	12	12	12	12	25.5	25.5	25.5
250	50	50	20	12	12	12	12	12	12	27.5	27.5	25.5
300	50	50	20	12	12	12	12	12	12	27.5	27.5	25.5
350	50	50	20	12	12	12	12	12	12	27.5	27.5	25.5
400	50	50	20	12	12	12	12	15	15	25.5	25.5	25.5
450	50	50	20	12	12	12	12	15	16	25.5	25.5	25.5
500	50	50	20	12	12	12	12	18.5	18.5	25.5	25.	25.5
600	50	50	20	12	12	12	12	18.5	22.5	25.5	25.5	25.5
700	50	50	20	12	12	12	12	18.5	22.5	25.5	25.5	25.5