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CODE 33 MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

Code Chart 33A:

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 1.5 volts, at closed throttle idle, to 4-4.5 volts at wide open throttle (low vacuum). If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery.

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

1. This step will determine if Code 33A is the result of a hard failure or an intermittent condition. Code 33A will set if:

^ MAP signal indicates greater than 84 kPa (low vacuum).
^ No Code 21 is set.
^ TPS less than 5%.
^ These conditions are present longer than 5 seconds.

2. This step simulates conditions for a Code 33B. If the ECM recognizes the change, the ECM and GRY wire and GRY/RED wire, are OK. If PPL/ORN wire 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 high. This information is used by the ECM as an indication of vehicles altitude and is referred to as BARO. Comparison of this BARO reading with a known good vehicles with the same sensor is a good way to check accuracy of a suspect sensor. Readings should be the same +/- 0.4 volts. A Code 33A will result if the GRY wire is open, or if the GRY/RED wire is shorted to voltage or to the PPL/ORN wire. If Code 33A is intermittent, Testing and Inspection