With 4L80 Automatic Transmission

Code 33 Manifold Absolute Pressure Sensor Circuit:

Wiring For Diagram For Code 33 Manifold Absolute Pressure Sensor Circuit:

CODE 33 - MANIFOLD ABSOLUTE PRESSURE SENSOR CIRCUIT


CIRCUIT DESCRIPTION:

The manifold absolute pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The PCM receives this information as a signal voltage that will vary from about 1 to 1.5 volts at idle to 4.0 to 4.5 volts at wide open throttle. If the MAP sensor fails, the PCM will substitute a fixed MAP value and use the Throttle Position Sensor (TPS) to control fuel delivery.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 33 will set when:

^ MAP signal voltage is too high.
Engine misfire or a low unstable idle may set Code 33.
^ TPS less than 4%.
^ These conditions exist longer than 5 seconds.


2. This step simulates conditions for a code 34. If the PCM reconizes the change, the PCM and CKT 474 and CKT 432 are ok. If CKT 455 is open, there may also be a stored code 23.

DIAGNOSTIC AIDS:


With the ignition "ON" and the engine stopped, the manifold pressure is equal to atmospheric pressure and the signal voltage will be to high. This information is used by the PCM as an indication of vehicle altitude. Comparison of this reading with known good vehicle with the same sensor is a good way to check the accuracy of a suspected bad sensor. Readings should be the same +/- .4 volt.
A code 33 will result if CKT 455 is open or if CKT 432 is shorted to voltage or to CKT 474.

If code 33 is intermittent, SEE DIAGNOSIS BY SYMPTOM - NO TROUBLE CODES STORED.
Check all connections.
Disconnect sensor from bracket and twist sensor connections. Output changes greater than .1 volt indicates a bad connector or connections. If OK, replace sensor.