DTC 63

***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. Code 33 will set when:

^ Manifold pressure greater than 75.3 kPa (A/C "OFF") 81.2 kPa (A/C "ON).
^ Throttle angle less than 2%.
^ Above conditions met for 2 seconds.
^ Engine misfire or low unstable idle may set a Code 63.

2. With the MAP sensor disconnected, the ECM should see a low voltage if the ECM and wiring are ok.


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.

^ If idle is rough or unstable, refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/STALLS/ROUGH, UNSTABLE OR INCORRECT IDLE.

^ An open in circuit 455 or the connection will result in a Code 63.

^ 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.