The manifold absolute pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The engine control module (ECM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The ECM provides a ground on the low reference circuit. The MAP sensor provides a signal to the ECM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The ECM detects a low signal voltage at a low MAP, such as during an idle or a deceleration. The ECM detects 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 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 throttle position (TP) sensor is greater than 28 percent.

If a shared 5-volt reference circuit is shorted to ground or shorted to a voltage, other 5-volt reference circuits may be affected.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Engine Control Module Connector End Views

Electrical Information Reference

Scan Tool Reference

Engine Control Module Scan Tool Information

Special Tools Required

J 23738-A Vacuum Pump

1. Ignition ON, observe the DTC information with a scan tool. Verify DTC 81-5 Volt Reference Circuit out of Range is not set.

⇒	If DTC 81-5 Volt Reference Circuit out of Range is set, refer to DTC 81 for further diagnosis.

2. Engine idling with all accessories OFF, observe the DTC information with a scan tool. DTCs 33 or 34 should not set.

1. Ignition OFF, disconnect the harness connector at the MAP sensor.
2. Test for less than 5 ohms between the low reference circuit terminal A and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal C and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the ECM.

⇒	If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Test for 4.8-5.2 volts between the signal circuit terminal B and ground.

⇒	If less than the specified range, test the signal circuit for an open or a short to ground. If the circuit tests normal, replace the ECM.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

5. If all circuits test normal, test or replace the MAP sensor.

The ignition ON, engine OFF, MAP sensor scan tool value should decrease within +/- 4 kPa by the amount of vacuum applied with the J 23738-A . For example, at 92 kPa, the MAP sensor scan tool reading should be between 71-79 kPa with 5 in Hg (17 kPa) of vacuum applied to the sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.