GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 GMC C Sierra - 2WD 🢒 Engine 🢒 Engine Controls - 6.6L (LLY) 🢒 DTC P0299

Circuit Description

The boost pressure sensor measures the pressure inside the intake manifold. Pressure in the intake manifold is affected by turbocharger output, engine speed, accelerator pedal input, air temperature, and barometric pressure (BARO). A diaphragm within the boost pressure sensor is displaced by the pressure changes that occur from the varying load and operating conditions of the engine. The sensor translates this action into electrical resistance. The boost pressure sensor wiring includes 3 circuits. The engine control module (ECM) supplies a regulated 5 volts to the sensor on a 5-volt reference circuit. The ECM supplies a ground on a low reference circuit. The boost pressure sensor provides a signal voltage to the ECM, relative to pressure, on the boost pressure 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. Under these conditions, the ECM uses the boost pressure sensor to aid in diagnosis of the BARO sensor. 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 240 kPa (34 psi) when pressures are high, depending on the BARO. The boost pressure sensor has a range of 33 kPa (4 psi) to 255 kPa (36 psi). The ECM also uses the boost pressure sensor to provide engine overboost protection. The ECM calculates a predicted value for the boost pressure sensor. The ECM then compares the predicted value to the sensor input. If the ECM detects that the boost pressure sensor input is below the predicted range, this DTC will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0299 Turbocharger Engine Underboost

Conditions for Running the DTC
    • DTCs P0237, P2227, P2228, P2229 are not set.
    • The engine speed is between 500-3,600 RPM.
    • The engine speed does not vary more than 50 RPM.
    • The engine run time is more than 10 seconds.
    • DTC P0299 runs continuously within the enabling conditions.

Conditions for Setting the DTC
    • The ECM detects that the boost pressure input is 35 kPa below the calibrated value.
    • To obtain the desired boost, the ECM must command the turbocharger vanes closed further than expected.
    • One of the above conditions exist for more than 12 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Turn ON the ignition, with the engine OFF.
  2. Monitor the DTC information with a scan tool.

Is DTC P0045, P0046, P0652, P2563, P2564 or P2565 also set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3

Inspect the following components:

    • Inspect the air cleaner element for the following conditions:
       - Excessive dirt
       - Debris
       - Water saturation
    • Inspect the air intake duct for a leak or restriction.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 4

4

Observe the Boost Pressure Sensor parameter and the BARO parameter with a scan tool.

Is the difference between the values more than the specified value?

3 kPa

Go to Step 12

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Remove the boost sensor from the intake manifold. Refer to Turbocharger Pressure Sensor Replacement .
  3. Inspect for the following conditions:
    4. • A plugged sensor port
    • A damaged or leaking seal

Did you find and correct the condition?

--

Go to Step 23

Go to Step 6

6
  1. Connect the electrical connector to the boost sensor.
  2. Connect a J 23738-A Mityvac vacuum pump to the sensor port.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the Boost Pressure Sensor parameter with a scan tool.
  5. Slowly apply vacuum with the J 23738-A to the sensor until 10 inches Hg is reached.

Does the Boost Pressure Sensor parameter decrease?

--

Go to Step 7

Go to Step 20

7
  1. Observe the Boost Pressure Sensor parameter with a scan tool.
  2. Remove the vacuum from the sensor port.

Does the Boost Pressure Sensor parameter return to the value observed in Step 3?

--

Go to Step 8

Go to Step 20

8

Test the charge air cooler and connecting pipes and hoses for air leaks using the J 46091 Charge Air Cooler Tester.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 9

9

Inspect the exhaust system for the following conditions:

    • Leaks between the exhaust manifolds and the turbocharger--Refer to Exhaust Leakage .
    • Restrictions--Refer to Restricted Exhaust .
        
    • Aftermarket parts

Did you find and correct the condition?

--

Go to Step 23

Go to Step 10

10

Remove and inspect the turbocharger for wear or damage. Refer to Turbocharger Replacement and Turbocharger Cleaning and Inspection .

Did you find a condition with the turbocharger?

--

Go to Step 22

Go to Step 11

11
  1. Test for the following conditions:
    2. • Charge air leaks between the following components:
       - Air inlet tube
       - Intake manifold tube
       - Center intake manifold
       - Left and right intake manifolds
       - Left and right cylinder heads
    • Head gasket failure--Refer to Engine Compression Test .
    • Worn piston rings--Refer to Engine Compression Test .
  2. Repair as necessary.

Did you find and correct the condition?

--

Go to Step 23

Go to Intermittent Conditions

12

Test for an intermittent and for a poor connection at the boost pressure sensor connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 23

Go to Step 13

13
  1. Disconnect the boost pressure sensor.
  2. Measure the amperage between the 5-volt reference circuit and the low reference circuit, at the boost pressure sensor connector, with a DMM.

Is the amperage more than the specified value?

220 mA

Go to Step 14

Go to Step 15

14
  1. Connect a jumper wire between the 5-volt reference circuit and the signal circuit of the boost pressure sensor at the connector.
  2. Observe the Boost Pressure Sensor parameter with the scan tool.

Is the pressure more than the specified value?

254 kPa (36 psi)

Go to Step 20

Go to Step 17

15
  1. Disconnect the engine control module (ECM).
  2. Measure the resistance of the 5-volt reference circuit between the boost pressure sensor and the ECM, with a DMM.

Is the resistance more than the specified value?

5 ohms

Go to Step 19

Go to Step 16

16

Measure the resistance of the low reference circuit between the boost pressure sensor and the ECM with a DMM.

Is the resistance more than the specified value?

5 ohms

Go to Step 19

Go to Step 21

17

Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 23

Go to Step 18

18
  1. Disconnect the ECM.
  2. Measure the resistance of the boost pressure sensor signal circuit between the boost pressure sensor and the ECM with a DMM.

Is the resistance more than the specified value?

5 ohms

Go to Step 19

Go to Step 21

19

Repair the high resistance in the circuit. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 23

--

20

Replace the boost pressure sensor. Refer to Turbocharger Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 23

--

21

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 23

--

22

Replace the turbocharger. Refer to Turbocharger Replacement .

Did you complete the replacement?

--

Go to Step 23

--

23
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Perform the turbocharger learn procedure. Refer to Turbocharger Learn .
  5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 24

24

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK