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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 Manifold Absolute Pressure Sensor Diagnosis

Circuit Description

The manifold absolute pressure (MAP) sensor responds to changes in intake manifold pressure which gives an indication of the engine load. The MAP sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit, which is relative to the pressure changes in the manifold. With low MAP, such as during idle or deceleration, the PCM should detect a low MAP sensor signal voltage. With high MAP, such as ignition ON, engine OFF or wide open throttle (WOT), the PCM should detect a high MAP sensor signal voltage. The MAP sensor is also used in order to calculate the barometric pressure (BARO) when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 sets. If the PCM detects a MAP sensor signal voltage that is excessively high DTC P0108 sets.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step tests the MAP sensor's ability to correctly indicate BARO.

    2.

  2. The measurement noted in this step will be used in subsequent steps if the measurement does not exceed the specified value.

    3.

  3. This step calculates the resistance in the 5-volt reference circuit.

    4.

  4. This step calculates the resistance in the low reference circuit.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Inspect for the following conditions:

    • Disconnected, damaged, or incorrectly routed vacuum hoses
    • Missing or damaged manifold absolute pressure (MAP) sensor seal
    • Restrictions in the MAP sensor vacuum source
    • Intake manifold vacuum leaks

Did you find and correct the condition?

--

Go to Step 28

Go to Step 3

3

Important: The vehicle used for the comparison is not limited to the same type of vehicle as is being serviced. A vehicle known to provide an accurate reading is acceptable.

Do you have access to another vehicle in which the MAP sensor pressure can be observed with a scan tool?

--

Go to Step 4

Go to Step 5

4

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the MAP sensor pressure with a scan tool.
  3. Observe the MAP sensor pressure in the known good vehicle with a scan tool.
  4. Compare the values.

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

3 kPa

Go to Step 6

Go to Step 10

5

Important: The Altitude vs. Barometric Pressure table indicates a pressure range for a given altitude under normal weather conditions. Weather conditions consisting of very low or very high pressure and/or very low or very high temperature may cause a reading to be slightly out of range.

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the MAP sensor pressure with a scan tool. Refer to Altitude Versus Barometric Pressure .
  3. The MAP sensor pressure should be within the range specified for your altitude.

Does the MAP sensor indicate the correct barometric pressure?

--

Go to Step 6

Go to Step 10

6
  1. Observe the MAP sensor pressure with a scan tool.
  2. Start the engine.

Does the MAP sensor pressure change?

--

Go to Step 7

Go to Step 10

7
  1. Turn OFF the ignition.
  2. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness.
  3. Connect a J 23738-A Mityvac to the MAP sensor.
  4. Turn ON the ignition, with the engine OFF.
  5. Observe the MAP sensor pressure with the scan tool.
  6. Apply vacuum to the MAP sensor with the J 23738-A in 1 inch Hg increments until 15 inches Hg is reached. Each 1 inch Hg should decrease MAP sensor pressure by 3-4 kPa.

Is the decrease in MAP sensor pressure consistent?

--

Go to Step 8

Go to Step 10

8

Apply vacuum with the J 23738-A until 20 inches Hg is reached.

Is the MAP sensor pressure less than the specified value?

34 kPa

Go to Step 9

Go to Step 10

9

Disconnect the J 23738-A from the MAP sensor.

Does the MAP sensor pressure return to the value observed in step 4 or 5?

--

System OK

Go to Step 26

10

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

Did you find and correct the condition?

--

Go to Step 28

Go to Step 11

11
  1. Disconnect the MAP sensor electrical connector.
  2. Observe the MAP sensor parameter with the scan tool.

Is the voltage less than the specified value?

0.1 V

Go to Step 12

Go to Step 18

12

Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground with a DMM. Refer to Circuit Testing . Note the measurement as Supply voltage.

Is the voltage more than the specified value?

5.2 V

Go to Step 19

Go to Step 13

13

Is the voltage more than the specified value?

4.8 V

Go to Step 14

Go to Step 20

14
  1. Connect a test lamp and a DMM in series between the 5-volt reference circuit and the low reference circuit of the MAP sensor, at the harness connector.
  2. Measure the amperage, with the DMM. Note the measurement as Amperage.

Is the amperage equal to the specified value?

0 mA

Go to Step 23

Go to Step 15

15

  1. Remove the DMM from the circuit.
  2. Connect the test lamp between the 5-volt reference circuit and the low reference circuit of the MAP sensor, at the harness connector.
  3. Measure the voltage from the 5-volt reference circuit at the test lamp to a good ground, with the DMM. Note the measurement as Load voltage drop.

    4. Important: Before any calculations are performed, ensure that all measurements are converted to like units, for example, volts/amps or millivolts/milliamps.

  4. Subtract the Load voltage drop from the Supply voltage. Note the result as Supply voltage drop.
  5. Divide the Supply voltage drop by the Amperage.

Is the result more than the specified value?

5 ohms

Go to Step 21

Go to Step 16

16

  1. Measure the voltage from the low reference circuit of the MAP sensor at the test lamp to a good ground, with the DMM. Note the result as Low reference voltage drop.

    2. Important: Before any calculations are performed, ensure that all measurements are converted to like units, for example, volts/amps or millivolts/milliamps.

  2. Divide the Low reference voltage drop by the Amperage.

Is the result more than the specified value?

5 ohms

Go to Step 24

Go to Step 17

17
  1. Remove the test lamp.
  2. Connect a 3-amp fused jumper wire between the 5-volt reference circuit and the signal circuit of the MAP sensor, at the harness connector.
  3. Observe the MAP sensor parameter with the scan tool.

Is the voltage more than the specified value?

4.9 V

Go to Step 26

Go to Step 22

18

Test the MAP sensor signal circuit between the powertrain control module (PCM) and the MAP sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 28

Go to Step 25

19

Test the 5-volt reference circuit between the PCM and the MAP sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 28

Go to Step 25

20

Test the 5-volt reference circuit between the PCM and the MAP sensor for an open or for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 28

Go to Step 25

21

Test the 5-volt reference circuit between the PCM and the MAP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 28

Go to Step 25

22

Test the MAP sensor signal circuit between the PCM and the MAP sensor for the following conditions.

    • An open
    • A short to ground
    • High resistance

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 28

Go to Step 25

23

Test the low reference circuit between the PCM and the MAP sensor for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 28

Go to Step 25

24

Test the low reference circuit between the PCM and the MAP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 28

Go to Step 25

25

Test for shorted terminals and for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 28

Go to Step 27

26

Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 28

--

27

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

Did you complete the replacement?

--

Go to Step 28

--

28
  1. Reassemble the vehicle as necessary.
  2. Clear the DTCs with the scan tool.
  3. Start the engine.
  4. Operate the system in order to verify the repair.

Did you correct the condition?

--

Go to Step 29

Go to Step 2

29

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