Manifold Pressure/Vacuum Sensor: Testing and Inspection

Manifold Absolute Pressure Sensor Diagnosis

Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview






Typical Scan Tool Data






Circuit/System Description

The manifold absolute pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits:

* 5-volt reference circuit
* Low reference circuit
* MAP sensor signal circuit

The control module supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The control module also provides a ground on the low reference circuit. The MAP sensor provides a signal to the control module on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The control module should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The control module should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at a wide open throttle (WOT). The MAP sensor is also used in order to determine the barometric pressure (BARO). This occurs 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 control module monitors the MAP sensor signal for voltage outside of the normal range.

Diagnostic Aids

Poor idle characteristics may be due to uncontrolled fueling caused by an open or high resistance in the heated oxygen sensor (HO2S) 1 low signal circuit. Before replacing any component, ensure that this condition does not exist.

Circuit/System Testing

Always perform the Diagnostic System Check - Vehicle. Initial Inspection and Diagnostic Overview

1. Start the engine.
2. Monitor the DTC information with the scan tool.
3. If DTC P0641 or P0651 is also set then correct DTC P0641 or P0651 first.
4. Inspect for the following conditions:

* Disconnected, damaged, or incorrectly routed vacuum hoses
* MAP sensor disconnected from the vacuum source
* Restrictions in the MAP sensor vacuum source
* Intake manifold vacuum leaks
* Inspect for a properly functioning oxygen sensor.

5. With the ignition ON, and the engine OFF.
6. Disconnect the MAP sensor.
7. Measure for 4.8-5.2 volts from the 5-volt reference circuit of the MAP sensor to a good ground, with a DMM.

* If more than 5.2 volts, then test the circuit for a short to voltage. If the circuit tests normal, replace the control module.
* If less than 4.8 volts, then test the circuit for high resistance, an open, a short to ground, or an intermittent and poor connection or at the control module. If the circuit tests normal, replace the control module.

8. Use a scan tool and observe the MAP sensor for less than 12 kPa.

^ If the MAP sensor is more than 12 kPa then test the MAP sensor signal circuit for a short to voltage. If the circuit tests normal, replace the control module.

9. Use a 3-amp fused jumper wire and connect it between the MAP sensor 5-volt reference circuit and the MAP sensor signal circuit.
10. Use a scan tool and observe the MAP sensor for more than 103 kPa.

^ If the MAP sensor is less than 103 kPa, then test the MAP sensor signal circuit for a short to ground, an open, high resistance. If the circuit tests normal, replace the control module.

11. Turn OFF the ignition and allow the control module to power down.
12. Remove the MAP sensor from the engine vacuum source. Leave the MAP sensor connected to the engine harness.
13. Connect a J 23738-A to the MAP sensor.
14. Turn ON the ignition, with the engine OFF.
15. Observe the MAP sensor pressure with the scan tool.
16. 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. Monitor the MAP sensor pressure to see if the decrease in pressure is consistent.

^ If decrease in pressure is not consistent then, test for intermittent and poor connections at the MAP sensor. If connections test OK, replace the MAP sensor

17. Apply vacuum with the J 23738-A until 20 inches Hg is reached. Observe the MAP sensor pressure for less than 34 kPa.

^ If more than 34 kPa, test for an intermittent and for a poor connection at the MAP sensor. If connections test OK, replace the MAP sensor.

18. With a DMM measure for less than 5 ohms of resistance between the low reference circuit of the MAP sensor and battery negative post.

^ If the resistance is more than 5 ohms, then test the low reference circuit for a high resistance. If the circuit tests normal, replace the control module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Manifold Absolute Pressure Sensor Replacement
* Control Module References Programming and Relearning