Powertrain Controls - ECM/PCM

DTC 31 Chart:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold vacuum. The PCM provides the MAP sensor with a 5 volt reference and a sensor ground. The MAP sensor varies the signal on CKT 432 to PCM between 0 and 5 volts depending on manifold vacuum. As vacuum increases, the MAP signal voltage will decrease indicating low engine load. As vacuum decreases, the MAP signal voltage will increase indicating higher engine load. If the PCM detects the MAP sensor signal voltage higher than 5.06 volts, DTC 31 will set.

DTC 31 WILL SET WHEN
- DTC(s) 21 or 22 are not set.
- Engine is running and Throttle Position (TP) sensor is less than 21 degrees.
- MAP signal indicates eater than 5.06 volts (103.5 kPa)

ACTION TAKEN (PCM WILL DEFAULT TO)
- With a current DTC 31 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- The PCM will disable the long term fuel correction and substitute a default MAP value based on engine RPM and throttle position switch status.

DTC 31 WILL CLEAR WHEN
The fault no longer exists.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If DTC 38 is also set, CKT 452 is open or shorted to voltage because MAP sensor and IAT sensor share the same return.
2. If MAP sensor or circuitry are shorted, Tech 1 will read 103-105 kPa.
3. If Tech 1 data goes to 10-16 kPa with the sensor unplugged, the fault is in the sensor.
4. Checking CKT 432 for a short to battery. If wire OK, replace the PCM.

DIAGNOSTIC AIDS
If idle is rough or unstable, refer to Rough, Unstable or Incorrect Idle, Stalling in Diagnosis by Symptom. Rough, Unstable, or Incorrect Idle, Stalling
An open in CKT 452 or the connection will result in a DTC 31.
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. Headings should be the same ±0.4 volt.