Federal Emissions

Code 34 Diagnostic Chart:

Manifold Absolute Pressure (MAP) Sensor Circuit Diagram:

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 1-1.2 volts at idle (high vacuum) to 4-4.8 volts at Wide Open Throttle (WOT) (low vacuum). If the MAP sensor fails, the ECM will substitute a fixed MAP valve and use the TP sensor to control fuel delivery.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 34 will set if:
^ Engine RPM less than 600.
^ Manifold pressure reading less than 13 kPa.
^ Conditions met for .22 second.
OR
^ Engine RPM greater than 600.
^ Throttle angle over 20%.
^ Manifold pressure less than 13 kPa.
^ Conditions met for .22 second.

2. This test is to see if the sensor is at fault for the low voltage or if there is an ECM or wiring problem.

3. This simulates a high signal voltage to check for an open in CKT 432. If the test light is bright during this test, CKT 432 is probably shorted to ground. If Tech 1 (or equivalent) scan tool reads over 4 volts at this test, CKT 474 can be checked by measuring the voltage at terminal "C" (should be 5 volts).


DIAGNOSTIC AIDS:
^ An intermittent open in CKT 432 or CKT 474 will result in a DTC 34.

^ 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 Comparison of this 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 +/- .4 volt.

^ Check all connections. Make sure electrical connector remains securely fastened.


^ Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connections. Output changes greater than .1 volt indicates a bad connector or connections. If OK, replace sensor.

^ Refer to CHART C-1D, MAP sensor voltage output check for further diagnosis. Chart C-1D Manifold Absolute Pressure (MAP) Output Check