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Old 07-27-2017, 01:05 AM   #1 (permalink)
jjbced
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p0101 when going down hill

I have a 2005 duramax that's primarily used to pull my boats and travel trailer (3000-8000lbs) up and down long grades of 8-12%. When I am going down hill I downshift (typically to 3rd to keep rpm around 2500-2700) and after a mile or so throw a p0101 code (maf voltage low), truck goes into limp mode, it automatically downshifts to 2nd and redlines the engine. After slamming on the brakes to save the engine and SLOWLY getting to the bottom of the hill I start having to accelerate again. It takes about 3 minutes and the truck comes out of limp mode and runs great again. If I downshift down hill again within 5-10 minutes it'll go limp again quick, otherwise it runs fine. I have 4" cat back exhaust and am running the wretched spectre filter. Filter is clean and I'll admit, I wash it and rarely remember to re-oil so its safe to say the filter is very lightly oiled. Other than that the truck is all stock. I do have a android based radio so I run Torque Pro with a Bluetooth obd2 reader and when throwing the fault going down hill I looked at the live scan data... because realistically there is absolutely nothing else to do when you have a 6k lb trailer on the back and are stuck going 25mph down hill on a straight road at an 8% grade for 6 miles.... The live data showed the maf sensor was reading though I'll admit I forgot the numbers. Just yesterday I was pulling a 3k lb trailer and truck acted up again. This time my code reader was in my other car so I couldn't pull the numbers. I did check it this morning and am showing 27.1g/s at 680rpm with engine at 170 deg. The live data lags quite bit but I did romp on it a bit in town today without a load and its clearly reading the additional airflow. Hard to tell exactly what it was at due to the lag but I did see numbers in the 100's. To me this clearly shows the maf is working, which causes me to be at a complete loss! Any thoughts on what could be causing this?

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Old 07-30-2017, 03:44 PM   #2 (permalink)
jjbced
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Sadly no replies never the less, ove cleaned the maf, seafoamed the injectors and changed the oil. Yesterday I was towing 3-4k lb load yesterday and it happened again, this time i got it at a pending before it threw the code. My maf was showing about 80-90g when coasting down hill in lower gear. Any ideas???? I attached a pic of the pending fault codes

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Old 07-31-2017, 02:24 PM   #3 (permalink)
Ron Nielson
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Perhaps your answer lies with P0299

DTC P0299

Diagnostic Instructions


  • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure See: Testing and Inspection\Component Tests and General Diagnostics.
  • Review Strategy Based Diagnosis for an overview of the diagnostic approach See: Testing and Inspection\Component Tests and General Diagnostics.
  • Diagnostic Procedure Instructions provide an overview of each diagnostic category See: Testing and Inspection\Component Tests and General Diagnostics.
DTC Descriptor

DTC P0299: Turbocharger Engine Underboost

Circuit/System Description

The manifold absolute pressure (MAP) sensor measures the pressure inside the intake manifold. Pressure in the intake manifold is affected by turbocharger output, engine speed, accelerator pedal input, ambient air temperature, and barometric pressure (BARO). A diaphragm within the MAP pressure sensor is displaced by the pressure changes that occur from the varying load and operating conditions of the engine. The sensor translates these changes into electrical resistance. The engine control module (ECM) supplies a regulated 5 volts on the 5-volt reference circuit and a ground on a low reference circuit. The MAP sensor provides a signal voltage to the ECM, relative to intake manifold pressures, on the MAP sensor signal circuit. The ECM converts the signal voltage input to a pressure value. Under normal operation, the lowest pressure that can exist in the intake manifold is equal to the BARO. This occurs when the vehicle is operated at idle or when the ignition is ON while the engine is OFF. The highest manifold pressures occur when the turbocharger output is high. Manifold pressure can range from 58 kPa (8 psi) when pressures are low to more than 295 kPa (42.7 psi) when pressures are high, depending on the BARO. The MAP pressure sensor has a range of 43-365 kPa (6-53 psi). The ECM monitors the MAP sensor by comparing a calculated predicted value at a predetermined engine load and speed, to the actual sensor input.

Conditions for Running the DTC


  • DTCs P2564 or P2565 are not set.
  • The engine speed is between 800-3,000 RPM.
  • DTC P0299 runs continuously when the above conditions are met.
Conditions for Setting the DTC

The measured MAP pressure is more than 39 kPa below the expected range for 10 seconds.

Action Taken When the DTC Sets


  • DTC P0299 is a Type A DTC.
  • A message center or an indicator may display reduced engine power.
  • The ECM commands reduced engine power.
  • Diesel particulate filter (DPF) regeneration is inhibited.
Conditions for Clearing the DTC

DTC P0299 is a Type A DTC.

Diagnostic Aids


  • If the condition is intermittent. Refer to Testing for Intermittent Conditions and Poor Connections and Inducing Intermittent Fault Conditions See: Testing and Inspection\Component Tests and General Diagnostics.
  • A MAP sensor that is stuck at BARO, or is skewed 40 kPa lower than desired while under boost will cause this DTC to set.
  • If the vehicle passes the Circuit/System Verification Test, operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records list.
Reference Information

Schematic Reference

Engine Controls Schematics See: Powertrain Management\Diagrams\Electrical

Connector End View Reference

Component Connector End Views See: Diagrams

Description and Operation

Turbocharger System Description See: Powertrain Management\Fuel Delivery and Air Induction\Turbocharger\Description and Operation

Electrical Information Reference


  • Circuit Testing See: Testing and Inspection\Component Tests and General Diagnostics
  • Connector Repairs See: Testing and Inspection\Component Tests and General Diagnostics
  • Testing for Intermittent Conditions and Poor Connections See: Testing and Inspection\Component Tests and General Diagnostics
  • Wiring Repairs See: Testing and Inspection\Component Tests and General Diagnostics
DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions See: Diagnostic Trouble Code Descriptions\Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Scan Tool Testing and Procedures

Circuit/System Verification


  1. Verify that DTCs P003A, P0047, P0048, P046C, P0402, P0403, P0698, P0699, P2563, P2564 or P2565 are not set.
    • If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis See: Diagnostic Trouble Code Descriptions\Diagnostic Trouble Code (DTC) Type Definitions.
  1. Engine running, command the TC Vane Pos. Ctrl. Solenoid ON, while performing a snapshot of the induction data list. Perform the following actions during the snapshot: Refer to Scan Tool Snapshot Procedure See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Scan Tool Testing and Procedures.
2.1. Slowly increase the engine speed to 1,700 RPM for 5 seconds and then return the engine speed to idle. 2.2. Plot the snapshot and verify that the MAP sensor parameter increases smoothly and follows the Engine Speed parameter as the engine speed is increased, and then returned to idle.
  • If the MAP parameter plot slope is not a straight line with even the RPM change, replace the MAP sensor.
  1. Operate the vehicle within the Conditions for Running the DTC to verify that the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing

Important: Perform the Repair Verification after completing the Circuit/System Testing.


  1. Verify the integrity of the air induction system, the turbocharger ducts and hoses by inspecting for the following conditions:
    • Any damaged components
    • Any loose or improperly installed components
    • A wet or restricted air filter
    • Any exhaust leaks before the turbocharger
    • Any exhaust restrictions after the turbocharger
    • Any snow or ice build-up at the air cleaner and MAF sensor
    • Any water, snow, ice build-up, restrictions or coking at the MAP sensor
  1. Test the charge air system for air leaks. Refer to Charge Air Cooler Diagnosis for Full System Air Leak Test See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics.
  2. Test the turbocharger oil supply feed. Refer to Turbocharger Lack of Oil Supply See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics.
  3. Inspect the turbocharger oil supply tube for restrictions.
    • If a restriction is found, clean or replace the oil supply tube as necessary.
  1. Inspect the turbocharger for debris, worn impeller and turbine blades, or damage Refer to Turbocharger Cleaning and Inspection See: Engine, Cooling and Exhaust\Engine\Service and Repair\Overhaul.
    • If worn or damaged turbocharger blades or vanes are found, replace the turbocharger assembly.
  1. If the induction system, charger air cooler system, the turbocharger, and the turbocharger oil supply test normal, replace the MAP sensor.
Repair Instructions


  • Diesel Particulate Filter (DPF) Service Regeneration See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics
  • Manifold Absolute Pressure Sensor Replacement See: Powertrain Management\Fuel Delivery and Air Induction\Turbocharger\Service and Repair
  • Turbocharger Replacement See: Powertrain Management\Fuel Delivery and Air Induction\Turbocharger\Service and Repair
  • Turbocharger Oil Feed Pipe Replacement See: Engine, Cooling and Exhaust\Engine\Oil Line, Turbocharger\Service and Repair
Repair Verification


  1. Install any components or connectors that have been removed or replaced during diagnosis.
  2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced.
  3. Clear the DTCs.
  4. Turn OFF the ignition for 60 seconds.
  5. Duplicate the Conditions for Running the DTC and use the freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to the Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure See: Diagnostic Trouble Code Descriptions\Diagnostic Trouble Code (DTC) Type Definitions.
  6. If any service has been performed on the turbocharger or on the turbocharger components, a turbocharger relearn must be performed. Failure to perform the turbocharger learn procedure may cause this DTC to set. Refer to Turbocharger Learn See: Powertrain Management\Fuel Delivery and Air Induction\Turbocharger\Testing and Inspection.
  7. Perform the Diesel Particulate Filter (DPF) Service Regeneration See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics.
__________________
Ron Nielson

2008 2500HD LT CCLB/Ally. Line-X, B&W Companion, MaxLoader Springs, Edge Insight CTS, Kennedy Custom ECM
2009 Arctic Fox 5er, Silver Fox Edition 29-5T, 3.6 Onan LPG, SteadyFast Stabilizers
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