Powertrain Controls - ECM/PCM

Trouble Code 34 Chart:

MAP Sensor Wiring Schematic:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure. MAP is the inverse of vacuum, so as MAP increases such as during wide open throttle, vacuum decreases. The MAP sensor should indicate approximately 1-2 volts at idle, and between 4 and 5 volts at wide open throttle. MAP is one of the most important inputs used by the Powertrain Control Module (PCM) for calculating fuel delivery.

DIAGNOSTIC TROUBLE CODE (DTC) 34 WILL SET WHEN
Engine speed is greater than 500 RPM, throttle angle is greater than 3% and MAP is less than 11 kPa. All conditions must be met for 3 seconds.

ACTION TAKEN (PCM) WILL DEFAULT TO
A default table of MAP values will be used by the PCM to calculate air flow. The Malfunction Indicator Lamp (MIL) will become illuminated and MAP values on the Tech 1 (or equivalent) will become minimum (11 kPa).

DTC 34 WILL CLEAR WHEN
A current DTC 34 will clear when the MAP value exceeds the minimum low MAP threshold value. A History DTC 34 will clear after 50 consecutive ignition key cycles without a current DTC 34 being stored.

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

1. This test is to see if the sensor is at fault for the low voltage or if there is a PCM or wiring problem.
2. This simulates a high signal voltage to check for an open in circuit 432. If the test light is bright during this test, circuit 432 is probably shorted to ground. If Tech 1 scan tool reads over 4 volts at this test, circuit 416 can be checked by measuring the voltage at terminal "C" (should be 5 volts).

DIAGNOSTIC AIDS
An intermittent open in circuit 432 or circuit 416 will result in a DTC 34.
With the ignition "ON" and engine stopped, the manifold pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the PCM 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 ± 0.4 volt.

NOTE: Check all connections and make sure electrical connector remains securely fastened for the following test.

Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connections. Output changes greater than 0.1 volt indicates a bad connector or connections. If OK, replace sensor. For further diagnosis refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C-1D. Chart C-1D Manifold Absolute Pressure (MAP) Output Check
Refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis by Symptom / Intermittents. - Intermittent Malfunctions