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Discussion Starter #1
Well, doesn't that just beat all.

2003 C4500 LB7, 78,000 miles, bone stock work truck.

Truck has intermittent low power and no boost. MAP and BARO are showing the same numbers.

Wastegate flapper is intact. Turbo spins properly. I backprobed the signal wire on the MAP sensor and I had Zero. Do we just have a dead MAP? I don't have one to swap it with.

After reading some, it seems to me that on an LB7:

No boost + smoke = turbo problem or boost leak,

No boost + no smoke = no fueling.

If I'm right, then we aren't fueling for some reason.

Is there another way to test the MAP sensor? I have a Solus scanner so I can gather data if I knew what to gather and how to interpret it.
 

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Discussion Starter #4
Wow. I would have thought that this was a more common problem, but apparently it's not.
 

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Discussion Starter #5
Interesting. I have a notification via Email that RamblinRodney replied to this thread, but his post isn't here.

He suggested swapping the MAP sensor with the BARO sensor. But where is the BARO sensor?
 

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Interesting. I have a notification via Email that RamblinRodney replied to this thread, but his post isn't here.
He suggested swapping the MAP sensor with the BARO sensor. But where is the BARO sensor?
I did post that then deleted because I seen someone suggested swap your MAP sensor with your BARO sensor then I looked up the two and they had different part numbers so that didn't make sense to do. I also reread your first post and seen that your MAP and BARO are showing the same numbers so I took it for granted that you knew where it was at.
This is an 03 LB7 2500 HD so I don't know if it's the same as your truck but it should be close.
(9) GM Part 12623671 SENSOR,TURBO PRESS(MAP) ACDelco #213-4658)
(24) GM Part 12615136 SENSOR,BARO PRESS (ACDelco #213-1631)
http://www.wholesalegmpartsonline.com/showAssembly.aspx?ukey_assembly=375177&ukey_make=1024&ukey_model=20287&modelYear=2003&ukey_category=19455
There are a lot of threads and posts on what your MAP and BARO sensor readings should be at idle.
 

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Your not getting no responses to this thread most likely because you say you have no codes.
I'm done with this thread. Every thing I've posted is because of the search feature.
This is one persons readings.
At idle, at sea level, your Boost sensor should read 14-15 PSI. Keep in mind your ECM subtracts what your BARO(this sensor is the one that reads in inHg) sensor is reading from your Boost sensor reading meaning Boost-Baro=Actual boost. Your Baro sensor should read around 29inHg give or take a couple depending on altitude and weather conditions. Bad weather will typically read lower and good weather will typically read higher. If you watch a weather report local to you, and they give the Baro pressure, you should be able to go outside and an see your truck reading about the same.


Baro and MAP should read the same with the engine not running and the key turned on. The number will all depend where you are at but at close to sea level it will be 100.

DTC P2227
Circuit Description
The barometric pressure (BARO) sensor measures the pressure of the atmosphere. This pressure is affected by altitude and weather conditions. A diaphragm within the BARO sensor is displaced by the pressure changes that occur from varying altitudes and weather conditions. The sensor translates this action into electrical resistance. The BARO 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 BARO sensor provides a signal voltage to the ECM, relative to the pressure changes on the BARO sensor signal circuit. The ECM converts the signal voltage input to a pressure value.

Changes in BARO due to weather are relatively small, while changes due to altitude are significant. Pressure can range from 56 kPa at an altitude of 4267 meters (14,000 feet), to 105 kPa at or below sea level. The BARO sensor has a range of 8-207 kPa. The ECM uses the BARO sensor input for fuel delivery and other diagnostics.

Within the ECM, the diagnostic compares the BARO sensor input to the boost pressure sensor input. If the ECM detects that the inputs are not within a specified amount of each other, DTC P2227 sets.

DTC Descriptor
The following procedure supports the following DTC:

DTC P2227 Barometric Pressure (BARO) Sensor Performance

Conditions for Running the DTC
DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0237, P0238, P0299, P0335, P0336, P0500, P2228, P2229 is not set.
The engine speed is between 580-900 RPM.
The engine run time is more than 8 seconds.
The vehicle speed is less than 40 km/h (25 mph).
The accelerator pedal position (APP) is less than 69 percent.
The engine coolant temperature is more than 20°C (68°F).
The mass air flow (MAF) is less than 50 g/s.
The power take-off (PTO) is not active.
The above conditions are met for 5 seconds.
DTC P2227 runs continuously once the above conditions are met.
Conditions for Setting the DTC
The ECM detects that the difference between the BARO pressure and the boost pressure is more than 15 kPa for 6 seconds.

Action Taken When the DTC Sets-Federal
The control module stores the DTC information into memory when the diagnostic runs and fails.
The MIL will not illuminate.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
The driver information center, if equipped, may display a message.
Action Taken When the DTC Sets-California
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.

Test Description
The numbers below refer to the step numbers on the diagnostic table.

This step tests the ability of the boost pressure sensor to correctly indicate barometric pressure.

This step tests the circuits and the controller output.

This step test the circuits and the controller output.

Step
Action
Values
Yes
No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module (ECM) Connector End Views or Engine Controls Connector End Views

1
Did you perform the Diagnostic System Check - Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2
Turn ON the ignition, with the engine OFF.
Observe and record the BARO parameter with a scan tool.
Compare the barometric pressure (BARO) value to the range specified in the altitude vs. barometric pressure table. Refer to Altitude vs Barometric Pressure .
Is the BARO parameter within the range specified?
--
Go to Step 3
Go to Step 7

3
Observe and record the Boost Pressure Sensor parameter with a scan tool.
Compare the Boost Pressure Sensor value to the range specified in the altitude vs. barometric pressure table. Refer to Altitude vs Barometric Pressure .
Is the Boost Pressure Sensor parameter within the range specified?
--
Go to Step 4
Go to Step 13

4
Connect a J 23738-A Mityvac to the BARO sensor port.
Observe the BARO parameter with a scan tool.
Apply vacuum with the J 23738-A until 10 inches Hg is reached.
Does the BARO parameter decrease?
--
Go to Step 5
Go to Step 24

5
Start the engine.
Operate the vehicle, at a consistent altitude, within the Conditions for Running the DTC.
Observe the BARO parameter with a scan tool.
Does the BARO parameter change more than the specified value?
15 kPa
Go to Step 7
Go to Step 6

6
Operate the vehicle, at a consistent altitude, within the Conditions for Running the DTC.
Observe the Boost Pressure Sensor parameter and the BARO parameter with a scan tool.
Is the difference between the Boost Pressure Sensor parameter and the BARO parameter more than the specified value?
15 kPa
Go to Step 13
Go to Intermittent Conditions

7
Test for an intermittent and for a poor connection at the BARO sensor connector. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 27
Go to Step 8

8
Disconnect the BARO sensor.
Measure the amperage between the 5-volt reference circuit and the low reference circuit, at the BARO sensor connector, with a DMM.
Is the amperage more than the specified value?
170 mA
Go to Step 9
Go to Step 10

9
Connect a jumper wire between the 5-volt reference circuit and the BARO sensor signal circuit at the BARO sensor connector.
Observe the BARO parameter with a scan tool.
Is the pressure more than the specified value?
205 kPa
Go to Step 24
Go to Step 19

10
Test for an intermittent and for a poor connection at the engine control module (ECM). Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 27
Go to Step 11

11
Disconnect the ECM.
Measure the resistance of the 5-volt reference circuit between the BARO sensor and the ECM, with a DMM.
Is the resistance more than the specified value?
5 ohms
Go to Step 23
Go to Step 12

12
Measure the resistance of the low reference circuit between the BARO sensor and the ECM, with a DMM.

Is the resistance more than the specified value?
5 ohms
Go to Step 23
Go to Step 26

13
Test for an intermittent and for a poor connection at the boost pressure sensor connector. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 27
Go to Step 14

14
Disconnect the boost pressure sensor.
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?
170 mA
Go to Step 15
Go to Step 16

15
Disconnect the ECM.
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 23
Go to Step 20

16
Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 27
Go to Step 17

17
Disconnect the ECM.
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 23
Go to Step 18

18
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 23
Go to Step 26

19
Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 27
Go to Step 21

20
Connect the ECM.
Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the boost sensor and the signal circuit of hte boost sensor.
Turn ON the ignition, with the engine OFF.
Observe the Boost Pressure Sensor parameter with a scan tool.
Is the Boost Pressure Sensor parameter more than the specified value
254 kPa (36 PSI)
Go to Step 25
Go to Step 22

21
Disconnect the ECM.
Measure the resistance of the BARO sensor signal circuit between the BARO sensor and the ECM, with a DMM.
Is the resistance more than the specified value?
5 ohms
Go to Step 23
Go to Step 26

22
Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
--
Go to Step 27
Go to Step 26

23
Repair the high resistance in the circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?
--
Go to Step 27
--

24
Replace the BARO sensor. Refer to Barometric Pressure (BARO) Sensor Replacement .

Did you complete the replacement?
--
Go to Step 27
--

25
Replace the boost pressure sensor. Refer to Boost Pressure Sensor Replacement .

Did you complete the replacement?
--
Go to Step 27
--

26
Replace the ECM. Refer to Engine Control Module (ECM) Replacement .

Did you complete the replacement?
--
Go to Step 27
--

27
Clear the DTCs with a scan tool.
Turn OFF the ignition for 30 seconds.
Start the engine.
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 28

28
Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List
System OK
 

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Discussion Starter #8
Thanks Rodney. There is some stuff in there that can help me track down if the Boost sensor is working properly.
 

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Discussion Starter #9
The boost sensor is working properly right now.

I was watching boost with my scanner and when I unplugged it, it went from 26.X to 14.X. Then I hooked my mityvac up to the sensing port and pulled a vacuum and the pressure dropped. I put the hose on the pressure port of the mityvac and the pressure went up.

I then hooked it all up and ran it and it ran perfect. Had good boost, power and no codes.

So now what? This has been an intermittent issue so the only thing I can think of is to go out every morning and drive it around the block a couple of times to see if it still has power.
 
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