Powertrain Controls - ECM/PCM

DTC 33 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.

DTC 33 WILL SET WHEN
- MAP is greater than 80 kPa.
- TP sensor is less than 12%.
- VSS is less than 1 mph.
- DTC 21 or 22 is not set.
- Above conditions are met for 10 seconds.

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 will determine if DTC 33 is the result of a hard failure or an intermittent condition.
2. This step simulates conditions for a DTC 34. If the PCM recognizes the change, the PCM, CKT 474 and CKT 432 are OK. If CKT 452 is open, there may also be a stored DTC 23.

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