Powertrain Controls - ECM/PCM

DTC 33 Map Circuit:

MAP Sensor Wiring Schematic:

CIRCUIT DESCRIPTION
The Manifold Absolute Pressure (MAP) sensor responds to changes in the intake manifold pressure. MAP is the inverse of vacuum, so as MAP increases such as during wide open throttle, vacuum decreases. The MAP sensor should indicate approximately 1 - 2 volts at idle, and between 4 and 5 volts at wide open throttle. MAP is one of the most important inputs used by the Powertrain Control Module (PCM) for calculating fuel delivery.

DIAGNOSTIC TROUBLE CODE (DTC) 33 WILL SET WHEN
No current DTC 21 or 22 is present, MAP is greater than 84 kPa (A/C "OFF") 87 kPa (A/C "ON"), throttle angle is between 3% and 30% and held steady. All conditions met for 4 seconds.

ACTION TAKEN (PCM) WILL DEFAULT TO
A default table of MAP values will be used by the PCM to calculate air flow. The Malfunction Indicator Lamp (MIL) will become illuminated and MAP values on the Tech 1 (or equivalent) will become maximum (5 volts).

DTC 33 WILL CLEAR WHEN
A current DTC 33 will clear when the MAP value falls below the calibrated high MAP threshold. A History DTC 33 will clear after 50 consecutive key cycles without a current DTC 33 being stored.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Engine misfire or an unstable idle may set DTC 33.
2. With the MAP sensor disconnected, the PCM should see a low voltage if the PCM and wiring are OK.


DIAGNOSTIC AIDS
If idle is rough or unstable, refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis By Symptom. Rough, Unstable, or Incorrect Idle, Stalling

An open in circuit 469 or the connection will result in a DTC 33.
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. Readings should be the same ± 0.4 volts.

NOTE: Check all connections. Make sure electrical connector remains securely fastened for the following test.

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 connections. If OK, replace sensor. For further diagnosis refer to Computers and Controls / System Diagnosis / Procedures / Diagnostic Charts / Chart C1D. Chart C-1D Manifold Absolute Pressure (MAP) Output Check

Refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis by Symptom / Intermittents. - Intermittent Malfunctions