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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Malibu 🢒 Engine 🢒 Engine Controls - 3.1L (LG8) 🢒 Manifold Absolute Pressure Sensor Circuit Diagnosis

Circuit Description

The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). The MAP sensor signal voltage to the PCM varies from below 2.0 volts at idle (high vacuum) to above 4.0 volts with the key on, engine not running, or engine running at wide open throttle (low vacuum).

The MAP sensor is used to determine manifold pressure changes while the linear EGR flow test diagnostic is being run to determine engine vacuum level for other diagnostics and to determine barometric pressure (BARO). The PCM monitors the MAP signals for voltages outside the normal range of the MAP sensor. If the PCM detects a MAP signal voltage that is excessively high, DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage will be set. If the PCM detects a MAP signal voltage that is excessively low, DTC P0107 Manifold Absolute Pressure (MAP) Sensor Circuit Low Voltage will be set.

The PCM also uses the MAP Sensor for throttle position sensor performance. If the PCM detects a TP in an out of range condition, when the MAP reading is above or below a calibrated amount then DTC P0121 Throttle Position (TP) Sensor Performance will be set.

Diagnostic Aids

Check for the following conditions:

    •  Monitor the MAP sensor using the scan tool. If the MAP sensor does not respond to throttle changes, check the 3X reference circuits from the ignition control module to the PCM.
         If the 3X reference signal is lost the PCM will only update the MAP sensor reading once per key cycle, when the engine is first started.
         Depending on where the MAP sensor voltage (high voltage or low voltage) is when the engine is started, the high or low voltage MAP sensor DTCs will set.
    •  Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs in Wiring Systems.
    •  Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the MAP display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems.
    •  Inspect for kinked and damaged vacuum hoses, ensure that a good vacuum source is available. Refer to Emission Hose Routing Diagram .

Step

Action

Value(s)

Yes

No

1

Was the Powertrain OBD System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Test for the following conditions:
    2. •  MAP sensor seal missing or damaged.
    •  Vacuum hoses disconnected, damaged, incorrectly routed.
    •  Intake manifold vacuum leaks.
    •  Vacuum leaks at throttle body.
    •  Vacuum leaks at EGR valve flange and pipes.
    •  Positive crankcase ventilation valve faulty, missing, or incorrectly installed.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 14

Go to Step 3

3
  1. Disconnect the MAP sensor electrical connector.
  2. Observe the MAP value displayed on the scan tool.

Is MAP value near the specified value?

0.0V

Go to Step 4

Go to Step 12

4
  1. Connect a test lamp between battery positive voltage and the MAP sensor signal circuit at the MAP sensor harness connector.
  2. Observe the MAP value displayed on the scan tool.

Is MAP value near the specified value?

4.95V

Go to Step 5

Go to Step 8

5
  1. Jumper the 5 Volt Reference A circuit and the MAP signal circuit together at the MAP sensor harness connector.
  2. Observe the MAP value displayed on the scan tool.

Is MAP value near the specified value?

4.95V

Go to Step 6

Go to Step 7

6
  1. Turn the ignition off.
  2. Disconnect the PCM and test the sensor ground circuit for high resistance, an open between the PCM and the MAP sensor or for a poor connection at the PCM. Refer to Testing for Continuity
  3. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 14

Go to Step 10

7
  1. Test the 5 Volt Reference A circuit for high resistance, an open between the PCM and the MAP sensor or a poor connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 14

Go to Step 9

8
  1. Turn the ignition off.
  2. Disconnect the PCM, and test the MAP sensor signal circuit for high resistance, an open, a short to ground, or a short to the sensor ground circuit.
  3. If a problem is found, repair as necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals Connector Repairs and Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 14

Go to Step 9

9
  1. Test the MAP sensor signal circuit for a poor connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Testing for Continuity , Repairing Connector Terminals and Connector Repairs in Wiring Systems.

Did the terminal require replacement?

--

Go to Step 14

Go to Step 13

10
  1. Test for a poor connection at the MAP sensor.
  2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 14

Go to Step 11

11

Replace the MAP sensor. Refer to MAP Sensor Replacement .

Is the action complete?

--

Go to Step 14

--

12
  1. Turn the ignition off.
  2. Disconnect the PCM.
  3. Turn the ignition on.
  4. Test the MAP signal circuit for a short to voltage or a short to the 5 Volt Reference A circuit.
  5. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step 14

Go to Step 13

13

Important: :  Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Is the action complete?

--

Go to Step 14

--

14

With engine idling, monitor MAP Sensor with scan tool while increasing engine RPM.

Does MAP sensor value change?

--

System OK

Go to Step 2