Powertrain Controls - ECM/PCM

DTC 34 Chart:

MAP Sensor Circuit:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor changes resistance based on manifold vacuum. The Powertrain Control Module (PCM) supplies a 5 volt reference and a ground. The MAP sensor voltage varies from 1.0 to 1.5V at idle (high vacuum) to 4.0-4.5V at wide open throttle (low vacuum). The MAP sensor is also used to measure barometric pressure, which allows the PCM to make adjustments for altitude changes.

DIAGNOSTIC TROUBLE CODE (DTC) 34 WILL SET WHEN
- DTC 21 is not set.
- MAP is less than 14 kPa.
- Engine speed is less than 1200 RPM or Throttle Position (TP) sensor is greater than 15.2%.
- All above conditions are met for 0.2 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate. The PCM will substitute a fixed MAP based on RPM value and use the 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
- 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 +/- 0.4 volt.
- 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.
- Refer to Chart C-1D Manifold Absolute Pressure (MAP) Output Check, MAP sensor voltage vs. atmospheric pressure for further diagnosis. Chart C-1D Manifold Absolute Pressure (MAP) Output Check
- If DTC 33 is intermittent, refer to Diagnosis by Symptom. Testing and Inspection