Code 33A Manifold Absolute Pressure (MAP) Sensor Circuit

SIGNAL VOLTAGE HIGH-LOW VACUUM




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 1.0 to 1.5 volts, at closed Throttle idle, to 4.0 - 4.5 volts at Wide Open Throttle (low vacuum). If the MAP Sensor fails, the ECM will substitute a fixed MAP value based on Throttle Position Sensor to control Fuel delivery.




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

1. This step will determine if Diagnostic Trouble Code (DTC) 33 is the result of a hard failure or an intermittent condition. A DTC 33 will set if:
- MAP Signal indicates greater than 95 kPa (low vacuum).
- Throttle Position Sensor less than 2%.
- No DTC 21A or DTC 21B is set.
- These conditions are present for a time longer than 5.3 seconds.

2. This step simulates conditions for a DTC 33B. If the ECM recognizes the change, the ECM, and BLU/ORG and GRY/RED wires are OK. If GRY wire is open, there may also be a DTC 23 stored.

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 and is referred to as Barometric pressure. Comparison of this Barometric pressure 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 volts.
- A DTC 33A will result if GRY wire is open, or if GRY/RED is shorted to voltage or to BLU/ORG wire.
- If DTC 33A is intermittent, refer to Diagnosis by Symptom. Symptom Related Diagnostic Procedures