DTC 33

Code Chart 33:

MAP Sensor Circuit:

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 to 2 volts at idle (high vacuum) to 4-4.8 volts at wide open throttle (low vacuum).

If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the 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:

^ Engine running.
^ Manifold pressure greater than 74 kPa (A/C "OFF"), 83.4 kPa (A/C "ON").
^ Throttle angle less than 2%.
^ Conditions met for 4.8 seconds.

Engine misfire, or a low unstable idle, may set DTC 33.

2. With the MAP sensor disconnected, the ECM should see a low voltage if the ECM and wiring is OK.

DIAGNOSTIC AIDS:
With the ignition "ON" and the engine stopped, 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. Comparison of this reading with a known good vehicle with the same sensor is a good way to check accuracy of a "suspect" sensor. Readings should be the same + .4 volt.

^ Check all connections.
^ Make sure electrical connector remains securely fastened.
^ Disconnect sensor from bracket and twist senor by hand (only) to check for intermittent connections. Output changes greater than .1 volt indicates a bad connector or connections. If OK, replace sensor.
^ For MAP sensor voltage output check diagnosis, Chart C-1D Manifold Absolute Pressure (MAP) Output Check