Circuit Description: Notes

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The DTC P1128 Manifold Absolute Pressure (MAP) Sensor Low Pressure diagnostic monitors the MAP sensor response to pressure changes in the intake manifold. The pressure changes occur based on engine load and the throttle valve opening. The MAP sensor has the following circuits:

A 5-volt reference circuit
A low reference circuit
A signal circuit

The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The PCM receives a low voltage on the signal circuit when manifold vacuum is high at idle or deceleration. The PCM receives a high voltage when manifold vacuum is low at wide open throttle (WOT) or when the ignition is ON and the engine is OFF. If the MAP sensor output is less than the expected value, a DTC P1128 can set.

The following table illustrates the difference between MAP kPa, signal voltage and engine vacuum.

DTC P1128

Engine Condition	MAP kPa	MAP Signal Voltage	Manifold Vacuum
Idle	Low	Low	High
Deceleration	Low	Low	High
Ignition ON, Engine OFF	High	High	Zero
Wide-Open Throttle	High	High	Low