Hummer H1 (2006+). Manual - part 73

OBD-136

On-Board Diagnostics

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DTC P0238 Turbo Charger Boost Sensor Circuit High Voltage (Figure OBD-40)

Figure OBD-40:   Turbocharger Boost Sensor Circuit

Circuit Description

The boost pressure sensor measures the pressure inside the intake manifold. Pressure in the intake manifold is affected by turbo-
charger 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 refer-
ence circuit. The boost pressure sensor provides a signal voltage to the ECM, relative to the pressure changes, 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 vehi-
cle 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 the diagnosis of the BARO sensor. The highest manifold pressure occur when the turbo charger output is high.
Manifold pressure can range from 58 kPa (8 psi) when pressure are low, to more than 240 kPa (34 psi) when pressure are high, de-
pending on the BARO. The boost pressure sensor has a range of 33-255 kPa (4-36 psi). The ECM also uses the boost pressure sen-
sor to provide engine overboost protection.

The ECM monitors the boost pressure sensor signal for pressure outside of the normal range. If the ECM detects a boost pressure
that is excessively high, DTC P0238 sets.

Conditions for Setting the DTC

The ECM detects that the boost pressure is more than 254 kPa (36 psi) for 2 seconds.

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 On-Board Diagnostics  OBD-137

5745804

Action Taken When the DTC Sets 

• The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diag-

nostic 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 consecu-
tive 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

Value(s)

Yes

No

    1

NOTE: Before clearing DTC(s) use the scan tool “Capture info”
to record Freeze Frame and Failure Records for reference, as data
will be lost when “Clear Info” function is used 

Was the “On-Board Diagnostic (OBD) System Check” per-
formed?

Go to step 2.

Go to OBD Sys-

tem Check.

    2

Observe the boost pressure sensor parameter with a scan tool.

Is the pressure less than the specified value?

254 kPa 

(36 psi)

Go to Step 4

Go to Step 3

    3

1.

Observe the Freeze Frame/Failure Records for this DTC.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

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 4 

Intemittent Go 

To Diagnostic 

Aids

    4

Monitor the Diagnostic Trouble Code (DTC) Information with a
scan tool.

Does the scan tool indicate that DTC P0653 is also set?

Go to Step 7 

Go to Step 5

    5

1.

Turn OFF the ignition.

2.

Disconnect the electrical connector of the boost pressure. 

3.

Turn ON the ignition, with the engine OFF.

Does the scan tool indicate that the Boost Pressure Sensor param-
eter is less than the specified value?

36 kPa (5 

psi)

Go to Step 6

Go to Step 8

OBD-138

On-Board Diagnostics

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    6

1.Remove the boost pressure sensor.

2.Connect a jumper wire between each of the terminals in the
boost pressure sensor harness connector and the corresponding
terminal at the boost pressure sensor. 

3.Measure the voltage from the low reference circuit 616 (OR/
BK) of the boost pressure sensor at the jumper wire terminal to a
good ground with a DVOM. 

Is the voltage more than the specified value?

0.2 Volts

Go to Step 9

Go to Step 10

    7

1.Turn OFF the ignition.

2.Disconnect the electrical connector of the boost pressure sen-
sor.

3.Turn ON the ignition, with the engine OFF.

Does the scan tool indicate that the Boost Pressure Sensor param-
eter is less than the specified value?

36 kPa (5 

psi)

Go to DTC 

P0653

Go to Step 8

    8

Test the signal circuit 615 (LG) of the boost pressure sensor for a
short to voltage. 

Did you find and correct the condition?

Go to Step 14

Go to Step 13

    9

Test the low reference circuit 616 (OR/BK) of the boost pressure
sensor for high resistance or an open between C76 pin 30 and pin
A of the boost sensor. 

Did you find and correct the condition?

Go to Step 14

Go to Step 11

    10

Inspect for poor connections at the boost pressure sensor. 

Did you find and correct the condition?

Go to Step 14

Go to Step 12 

    11

Inspect for poor connections at the engine control module
(ECM).

Did you find and correct the condition?

Go to Step 14 

Go to Step 13 

    12

Replace the faulty boost pressure sensor. 

Did you complete the replacement?

Go to Step 14 

    13

Replace the faulty ECM.

Did you complete the replacement?

Go to Step 14

    14

1.

Clear the DTCs with a scan tool.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

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 15

   15

1.

Using the Scan Tool select “Capture Info,” Review Info.” Are 
any DTC’s displayed that have not been diagnosed?

Go to the appli-

cable DTC 

table.

System OK.

Step

Action

Value(s)

Yes

No

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 On-Board Diagnostics  OBD-139

5745804

DTC P0299 Turbocharger Engine Underboost (Figure OBD-41)

Figure OBD-41:   Turbocharger Boost Sensor Circuit

Circuit Description

The boost pressure sensor measures the pressure inside the intake manifold. Pressure in the intake manifold is affected by turbo-
charger 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 refer-
ence circuit. The boost pressure sensor provides a signal voltage to the ECM, relative to pressure, on the boost pressure sensor sig-
nal 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 in-
put. If the ECM detects that the boost pressure sensor input is below the predicted range, this DTC will set.

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.