Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 33:

Manifold Absolute Pressure (MAP) Sensor Circuit:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The Powertrain Control Module (PCM) receives this information as a signal voltage that will vary from about 1 - 1.5 volts at idle to 4.0 - 4.8 volts at Wide Open Throttle (WOT).
The Tech 1 Scanner displays manifold pressure in kPa of pressure and voltage. Low pressure (high vacuum) indicates a low voltage while a high pressure (low vacuum) indicates a high voltage.

DTC 33 WILL SET WHEN
Less than 3% throttle angle, MAP greater than 80 kPa, MAP greater than 90 kPa with A/C "ON," RPM greater than 500 RPM, and DTCs 21 and 22 not set. All conditions met for 1 second.

ACTION TAKEN (PCM WILL DEFAULT TO)
If the MAP sensor fails, the PCM will calculate a MAP value based on throttle position and engine speed (RPM). The Malfunction Indicator Lamp (MIL) will illuminate.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Engine misfire or a low unstable idle may set DTC 33. Disconnect MAP sensor and system will go into backup mode. If the misfire or idle condition remains, refer to DIAGNOSIS BY SYMPTOM Testing and Inspection
2. If the PCM recognizes the low MAP signal, the PCM and wiring are OK.
3. An open in CKT 452 will result in a DTC 33.

DIAGNOSTIC AIDS
If the idle is rough or unstable, refer to Diagnosis By Symptom. Testing and Inspection
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 and is referred to as BARO. Comparison of this BARO 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, CHART C-1D can be used to test the MAP sensor. Chart C-1D Manifold Absolute Pressure (MAP) Output Check
If DTC 23, 66 or 71 is also set, check CKT 452 for faulty wiring or connections.
Refer to Diagnosis By Symptom. Testing and Inspection