DTC 33

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

CHART 1 OF 2

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

CHART 1 OF 2

MAP Sensor Wiring Circuit:

Circuit Description:
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1 to 1.5 volts at closed throttle (idle), to 4 to 4.5 volts at Wide Open Throttle (WOT) (low vacuum).

If the MAP sensor fails, the Engine Control Module (ECM) will substitute a fixed MAP value based on RPM and use the Throttle Position (TP) sensor to control fuel delivery. (Tech 1 will not show defaulted value.)

DTC 33 Will Set When:
^ No DTC 21.
^ MAP signal less then .25 volt.
^ RPM less than 1200 or greater than 12OO with TP sensor greater than 15%.
OR
^ MAP signal greater than 3.7 volts.
^ TP sensor less than 5%.
^ These conditions exist for 5 seconds or more.

Action Taken (ECM will default to): Malfunction Indicator Lamp (MIL) illuminates. ECM will substitute a fixed MAP value and use the Throttle Position (TP) sensor to control fuel delivery. (Tech 1 will not show defaulted value.)

DTC Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step determines if DTC 33 is the result of a hard failure or an intermittent condition.
2. if the ECM recognizes the change, the ECM and CKTs 474 and 432 are OK.
3. This step will determine if there is a wiring problem, vacuum problem or faulty MAP sensor.
4. This step checks to see if DTC 33 is the result of a hard failure or an intermittent condition.
5. Jumpering harness terminals "B" to "C" (5 volts to signal circuit) will determine if the sensor is at fault or if there is a problem with the ECM or wiring.
6. The scan tool may not display 12 volts. The important thing is that the ECM recognizes the voltage as more than 4 volts, indicating that the ECM and CKT 432 are OK.
7. If CKT 474 is open or shorted to ground, other DTC(s) may also be set.

Diagnostic Aids:
With the ignition "ON" and the engine not running, the manifold pressure is equal to atmospheric pressure and the signal voltage will be high. This information is used by the ECM 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" MAP sensor. Reading should be within +/- .4 volt.

If CKT 474 is shorted to ground or to CKT 455, other DTC(s) may also be set.

If DTC 33 is intermittent, refer to "Diagnosis By Symptom." - Intermittent Malfunctions