DTC 33

DTC 33 Chart Manifold Absolute Pressure Sensor Circuit:

Manifold Absolute Pressure Sensor Wiring Diagram:

Circuit Description:

The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1 - 1.5 volts at idle (high vacuum) to 4 - 4.8 volts at Wide Open Throttle (WOT) (low vacuum). The scan tool displays manifold pressure in kPa of pressure and voltage. Low pressure (high vacuum) displays a low voltage, while high pressure (low vacuum) displays a high voltage. If the MAP sensor fails, the ECM will substitute a MAP value based on RPM and Throttle Position (TP) sensor to control fuel delivery.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 33 will set when:

^ Less than 3% throttle.
^ MAP greater than 80 kPa.
^ MAP greater than 90 kPa with A/C "ON."
^ RPM greater than 500 RPM.
^ All above conditions met for 1 second.
^ Engine misfire or a low unstable idle may set DTC 33. Disconnect MAP sensor and system will go into backup mode. If the misfire or idle condition remains, see "Symptoms."

2. If the ECM recognizes the low MAP signal, the ECM and wiring are OK.

Diagnostic Aids:

If the idle is rough or unstable, Rough, Unstable, or Incorrect Idle, Stalling

An open in CKT 808 will result in a DTC 33. - Intermittent Malfunctions

With the ignition "ON," and the engine "OFF," the manifold pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the ECM as an indication of vehicle altitude and is referred to as BARO. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Reading should be the same + 0.4 volt. Chart C-1D Manifold Absolute Pressure (MAP) Output Check