Powertrain Controls - ECM/PCM

Diagnostic Trouble Code 33:

MAP Sensor Circuit:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The Engine Control Module (ECM) receives this information as a signal voltage that will vary from about 1 - 1.5 volts at idle to 4.5 - 4.8 volts at Wide Open Throttle (WOT).

A scan tool displays manifold pressure in volts. Low pressure (high vacuum) reads a low voltage while a high pressure (low vacuum) reads a high voltage.

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
Numbers below refer to circled numbers on the diagnostic chart.

1. Diagnostic Trouble Code (DTC) 33 will set when:

^ Engine is running.
^ TP sensor less than 4%.
^ MAP sensor signal voltage is too high (greater than 68 kPa of pressure or less than 9.5 in Hg of vacuum) for a time greater than 5 seconds.

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, refer to Diagnosis By Symptom. Testing and Inspection

2. If the ECM recognizes the low MAP signal, the ECM and wiring are 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 +/- 0.4 volt.

A DTC 33 will result if CKT 455 is open or If CKT 432 is shorted to voltage or to CKT 474.

If DTC 33 is intermittent, refer to Diagnosis By Symptom. Testing and Inspection

ELECTRICAL CHECKS
Make sure electrical connector remains securely fastened.

^ Check all connections.
^ Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connections. Output changes greater than 0.1 volt indicates a bad connector or connection. If OK, replace sensor.
^ Refer to Chart C-1D MAP Sensor Voltage Output Check for further diagnosis. Chart C-1D Manifold Absolute Pressure (MAP) Output Check