Powertrain Controls - ECM/PCM

DTC 34 - MAP Sensor Circuit (Signal Voltage Low - High Vacuum):

MAP Sensor Wiring Circuit:

Circuit Description:
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The Powertrain Control Module (PCM) receives this information as a signal voltage that will vary from about 1 to 1.5 volts at closed throttle (idle) to 4.5 - 4.8 volts at Wide Open Throttle (WOT) (low vacuum).

DTC 34 Will Set When:
^ The engine is running.
^ DTC 21 is not set.
^ MAP is less than 14 kPa.
^ Engine RPM is less than 1200 or TP sensor is greater than 15.2%.
^ Above conditions are met for .2 second.

Action Taken (PCM will default to): The Malfunction Indicator Lamp (MIL) will illuminate. The PCM will substitute a fixed MAP value and use the Throttle Position (TP) sensor to control fuel delivery. The cooling fan will enable.

DTC Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step determines if DTC 34 is the result of a hard failure or an intermittent condition.
2. Jumpering harness terminals "B" to "C" (5 volts to signal circuit) will determine if the sensor is at fault, or if there is a problem with the PCM or wiring.
3. The Tech 1 scan tool may not display 5 volts. The important thing is that the PCM recognizes the voltage as more than 4 volts, indicating that the PCM and CKT 432 are OK.

Diagnostic Aids: An open in CKT 432 or CKT 474 will result in a DTC 34. With the ignition "ON" and the engine "OFF," 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 +/- .4 volt. Also CHART C-1D can be used to test the MAP sensor. Refer to "Intermittents," in "Diagnosis By Symptom." - Intermittent Malfunctions

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 connection. If OK, replace sensor.

Refer to CHART C-1D, MAP sensor voltage vs. atmospheric pressure for further diagnosis. Chart C-1D Manifold Absolute Pressure (MAP) Output Check

NOTICE: Make sure electrical connector remains securely fastened.

NOTICE: After repairs use Tech 1 scan tool "Fuel Trim Reset" function to reset long term fuel trim to 128