GM Service Manual Online
For 1990-2009 cars only

Object Number: 32862  Size: MF
Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Manifold Absolute Pressure (MAP) sensor responds to changes in the intake manifold pressure (vacuum). A 5 volt reference is applied to the sensor on the 5 volt reference circuit. A variable resistor moves in relation to the manifold pressure and a voltage signal is sent back to the VCM on the MAP sensor signal circuit. This voltage signal will vary from 1.0-1.5 volts at closed throttle to 4.0-4.6 volts at wide open throttle (low vacuum). The VCM utilizes the MAP signal and the throttle position in order to determine the correct amount of fuel delivered to the engine. This DTC is a type D DTC.

Conditions for Setting the DTC

The following conditions will set the DTC:

    • No TP sensor DTCs are set
    • Throttle Position is no more than 0.4% when engine speed is no more than 1200 RPM
    • Or the Throttle Position is no more than 19.9% when engine speed is greater than 1200 RPM
    • MAP is greater than or equal to 4.34 volts

Action Taken When the DTC Sets

The VCM turns the MIL ON when this DTC is reported and 1 failure has occurred. The VCM substitutes a calculated value for the MAP sensor value so that acceptable performance is maintained.

Conditions for Clearing the MIL/DTC

The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.

Diagnostic Aids

With the ignition ON and the engine off, the manifold pressure is equal to atmospheric pressure with the signal voltage high. The VCM uses this information as an indication of the vehicle's altitude. Comparison of this reading with a known good vehicle using the same sensor is a good way to check the accuracy of a suspect sensor. Readings should be the same ±0.4 volts.

Refer to Intermittent Conditions .

Important: The electrical connector must remain securely fastened.

Important: Disconnect the sensor from the bracket and twist the sensor by hand (only) in order to check for intermittent connections. The output changes greater than 0.1 volt indicates a bad connector or connection. If OK, replace the sensor.

Important: After removing the MAP sensor from the intake manifold, replace the MAP Sensor to intake manifold seal.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. This step checks for a short to voltage on the 5 volt reference circuit.

  2. This step checks the integrity of the MAP sensor ground circuit.

  3. VCM pins GR12 and GR27 are spliced together inside the VCM. This step isolates the two pins from one another.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing the DTC(s) use the scan tool to record the Freeze Frame and Failure Records for reference. This data will be lost when the Clear Info function is used.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. If the engine idle is unstable, incorrect, or if the manifold vacuum at idle is less than the specified value, correct the fault before using this table. Refer to Engine Symptoms.
  2. Connect a scan tool.
  3. Engine at idle.

Does the scan tool display a voltage less than the specified value?

15 in Hg

4 V

Go to Step 3

Go to Step 4

3

  1. Turn the ignition OFF.
  2. Disconnect the MAP sensor electrical connector.
  3. Turn the ignition ON.

Does the scan tool display a voltage less than the specified value?

1 V

Go to Step 5

Go to Step 9

4

The DTC is intermittent. If no other DTCs are stored, go to Diagnostic Aids.

Are any additional DTCs stored?

--

Go to Applicable DTC Table

--

5

With a DVM connected to ground, probe the 5 volt reference circuit (at the MAP sensor harness connector).

Is the voltage greater than the specified value?

5.2 V

Go to Step 10

Go to Step 6

6

Probe the MAP sensor ground circuit (at the MAP sensor connector) with a test light to B+.

Is the test light ON?

--

Go to Step 7

Go to Step 14

7

Check the MAP sensor vacuum source for a restriction.

Was a problem found?

--

Go to Step 15

Go to Step 8

8

Replace the MAP sensor.

Is the action complete?

--

Go to Step 19

--

9

Check for a short to voltage in the MAP sensor signal circuit.

Was a problem found?

--

Go to Step 15

Go to Step 18

10

  1. Turn the ignition OFF.
  2. Disconnect the VCM gray connector.
  3. Turn the ignition ON.
  4. With a DVM connected to ground, measure the voltage on the 5 volt reference circuit (at the VCM harness connector).

Is the voltage greater than the specified value?

5.2 V

Go to Step 11

Go to Step 13

11

  1. Disconnect the EGR valve electrical connector.
  2. Measure the voltage on the 5 volt reference circuit (at the VCM harness connector).

Is the voltage greater than the specified value?

5.2 V

Go to Step 12

Go to Step 16

12

Repair the short to voltage on the 5 volt reference circuit

Is the action complete?

--

Go to Step 19

--

13

With a DVM to ground, measure the voltage on the VCM connector terminal GR 12.

Is the voltage greater than the specified value?

5.2 V

Go to Step 17

Go to Step 18

14

Repair the sensor ground circuit.

Is the action complete?

--

Go to Step 19

--

15

Repair as necessary.

Is the action complete?

--

Go to Step 19

16

Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .

Is the action complete?

--

Go to Step 19

--

17

Repair the short to voltage on the 5 volt reference circuit (terminal GR 12).

Is the action complete?

--

Go to Step 19

--

18

Replace the VCM.

Important: If the VCM is faulty, the new VCM must be programmed. Refer to VCM Replacement/Programming .

Is the action complete?

--

Go to Step 19

--

19

  1. Using the scan tool, select DTC, Clear Info.
  2. Start the engine and idle until normal operating temperature is reached.
  3. Select DTC, Specific, then enter the DTC number which was set.
  4. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic Ran and Passed?

--

Go to Step 20

Go to Step 2

20

Using the scan tool, select Capture Info, Review Info.

Are any additional DTCs displayed that have not been diagnosed?

--

Go to Applicable DTC Table

System OK