Powertrain Controls - ECM/PCM

DTC 33 MAP Sensor Circuit (Voltage High - Vacuum Low):

Manifold Absolute Pressure Sensor Wiring Circuit:

CIRCUIT DESCRIPTION:
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The PCM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4-4.5 volts at Wide Open Throttle (WOT). Voltage signals are lower at high altitudes.

A Tech 1 scan tool displays manifold pressure in volts. Low pressure (high vacuum) reads a low voltage while a high pressure (low vacuum) reads a high voltage.

If the MAP sensor fails the PCM will substitute a fixed MAP value and use the Throttle Position (TP) sensor to control fuel delivery

DTC 33 WILL SET WHEN:
No current DTC 21 or DTC 22 is present, MAP is greater than 80 kPa, throttle angle is less than 4%, engine running, vehicle speed is less than 2 mph with all conditions met for 5 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO):
A default table of MAP values will be used by the PCM to calculate air flow. The MIL will become illuminated and MAP values on the Tech 1 scan tool 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 value. A history DTC 33 will clear after 50 consecutive ignition key cycles without a current DTC 33 being stored.

DTC CHART 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
2. If the PCM recognizes the low MAP signal, the PCM and wiring are OK.

DIAGNOSTIC AIDS:
If idle is rough or unstable refer to "Symptoms," for items which can cause an unstable idle. Rough, Unstable, or Incorrect Idle, Stalling

An open in CKT 469 or the connection will result in a DTC 33.

With the ignition "ON," and the 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 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 +/- .4 volt.

If MAP sensor is suspected to be faulty, refer to CHART C-1D. Chart C-1D Manifold Absolute Pressure (MAP) Output Check

Refer to "Intermittents" in "Diagnosis By Symptom." - Intermittent Malfunctions