Powertrain Control Module - PCM

Diagnostic Trouble Code 34:

MAP Sensor Circuit:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The PCM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4-4.6 volts at Wide Open Throttle (WOT).

Tech 1 scan tool displays manifold pressure in volts. Low pressure (high vacuum) reads a low voltage while a high pressure (low vacuum) reads a high voltage.

DTC 34 WILL SET WHEN
^ When engine is less than 1000 rpm.
^ Manifold pressure reading less than 12 kPa.
^ Conditions met for 1 second.
OR
^ Engine speed is greater than 1000 rpm.
^ Throttle angle over 10%.
^ Manifold pressure less than 12 kPa, conditions met for 1 second.

ACTION TAKEN (PCM WILL DEFAULT TO)
If the MAP sensor fails, the PCM will substitute a fixed MAP value, use the Throttle Position (TP) sensor and rpm to control fuel delivery and the Malfunction Indicator Lamp (MIL) will illuminate.

DTC 34 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.

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 recognized the voltage as more than 4 volts, indicating that the PCM and CKT 432 are OK.

DIAGNOSTIC AIDS
An intermittent open in MAP sensor circuit or the 5 volt reference circuit 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. Reading should be the same +/- 0.4 volt. Also, MAP Output Check in C Charts / Manifold Absolute Pressure (MAP) Output Check can be used to test the MAP sensor. MAP Sensor Output Diagnosis

Refer to Diagnosis By Symptom / Intermittents - Intermittent Malfunctions

^ 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 connection. If OK, replace sensor.

NOTE: Make sure electrical connector remains securely fastened.

Refer to "MAP Output Check" in C Charts / Manifold Absolute Pressure (MAP) Output Check for further diagnosis. MAP Sensor Output Diagnosis