Engine Control Module - ECM

Diagnostic Trouble Code 34:

MAP Sensor Circuit:

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 1-1.5 volts at idle to 4-4.6 volts at Wide Open Throttle (WOT).

DTC 34 WILL SET WHEN
^ Engine is less than 1200 rpm.
^ Manifold pressure reading is less than 12 kPa for one second.
^ Engine speed is greater than 1200 rpm.
^ Throttle angle over 8%.
^ Manifold pressure less than 12 kPa for one second.

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

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 ECM or wiring.

3. The scan tool may not display 5 volts. The important thing is that the ECM recognized the voltage as more than 4 volts, indicating that the ECM and CKT 432 are OK.

DIAGNOSTIC AIDS
An intermittent open in CKT 432 or CKT 416 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 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. 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.

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