DTC 33

Fig. 049a Chart - Code 33:

Fig. 050 - Wiring Diagram for Code 33 Sensor. VIN Z:

CODE 33

MAP SENSOR CIRCUIT

SIGNAL VOLTAGE HIGH

(LOW VACUUM)

5.0L "F" SERIES

4.3L "B & G" SERIES

FUEL INJECTION (TBI)

Circuit Description: The Manifold Absolute Pressure Sensor (MAP) 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 Throttle Position Sensor (TPS) to control fuel delivery.

A "Scan" displays manifold pressure in volts. Low pressure (high vacuum) reads as a low voltage, high pressure (low vacuum) reads as a higher voltage.

Test Description: Numbers below refer to circled numbers on Diagnostic Charts.

1. This step will determine if Code 33 is the result of a hard failure or an intermittent condition.
A Code 33 will set if:
MAP signal indicates greater than 68 kPa (low vacuum).
TPS less than 4%.
These conditions for a time longer than 5 seconds
A low unstable idle or engine misfire may set a code 33. By disconnecting the MAP sensor the system will go to a backup mode. If the condition remains see DIAGNOSIS BY SYMPTOMS.

2. This step simulates conditions for a Code 34. If the ECM recognizes the change, the ECM, and CKTs 416 and 432, are OK. If CKT 469 is open, there may, also, be a stored Code 23.

Diagnostic Aids:

The ignition "ON", engine stopped; voltage chart at the right may be used to determine the accuracy of the MAP sensor. This boltage reading is used by ECM as a Barometric pressure reading.
A Code 33 will result if CKT 469 is open, or if CKT 432 is shorted to voltage or to CKT 416.
If Code 33 is intermittent, refer to DIAGNOSIS BY SYMPTOM.