Powertrain Controls - ECM/PCM

Code 33 Chart:

Code 33 Wiring Diagram:

***UPDATED BY TSB # 90-6-27 DATED APRIL 1990


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 idle, when manifold pressure is low (high vacuum), to 4.5 - 4.8 volts at wide open throttle (low vacuum or high pressure).

If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the throttle position sensor (TPS) to control fuel delivery.


NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.

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

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

Code 33 will set when:

- MAP signal is to high. (Low vacuum).
- TPS less than 2%.
- Above conditions met for longer than 5 seconds.

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

DIAGNOSTIC AIDS:

- With the ignition "ON and the engine stopped, the manifold pressure will be 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 the accuracy of a suspect sensor. Readings should be the same +/- 0.4 volt.

- A code 33 will result if circuit 469 is open or if circuit 432 is shorted to voltage or to circuit 416.

- If code 33 is intermittent, refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.

- Make sure electrical connection 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 indicate a bad connector or connection. If ok, replace sensor. Refer to CHART C-1D, MAP sensor voltage output check for further diagnosis.