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HOMESERVICE MANUALSFORD2018F-450 SUPER DUTY LARIAT, 4D PICKUP CREW CAB, 4WDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCEMODE 6 - 2017-18 FORD - DIESELBOOST PRESSURE CONTROL SYSTEM MONITORINGUNDERBOOST MONITORING
2018 Ford F-450 Super Duty Lariat, 4D Pickup Crew Cab, 4WD

UNDERBOOST Monitoring

2018 Ford F-450 Super Duty Lariat, 4D Pickup Crew Cab, 4WDSECTION 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
RENDER: 1.0x

NO RELATED

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.