Engine Control Module - ECM

DTC 33 Chart:

DTC 33 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 1-1.5 volts at closed throttle (idle) to 4-4.6 volts at Wide Open Throttle (WOT) (low vacuum).

DTC 33 Will Set When:

^ MAP signal voltage is too high (low vacuum) 68kPa.

^ TP signal less than 2%.

^ These conditions exist longer than 5 seconds.

^ Engine misfire or a low unstable idle may set DTC 33.

Action Taken (ECM will default to): The Malfunction Indicator Lamp (MIL) will illuminate and the ECM will substitute a fixed MAP value and use the Throttle Position (TP) sensor and RPM to control fuel delivery.

DTC 33 Will Clear When: Conditions for fault are no longer present and Tech 1 "Clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and ECM B fuse is removed for 10 seconds.

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 ECM recognizes the change, the ECM and CKT 416 and CKT 432 are OK. If CKT 455 is open, there may also be a stored DTC 23.

Diagnostic Aids: 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 ECM 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 +/- .4 volt.

A DTC 33 will result if CKT 455 is open or if CKT 432 is shorted to voltage or to CKT 416.

If DTC 33 is intermittent, refer to DIAGNOSIS BY SYMPTOM/ INTERMITTENTS - Intermittent Malfunctions.

^ Check all connections.

^ Disconnect sensor from bracket and twist sensor connections. Output changes greater than .1 volt indicates a bad connector or connection. If OK, replace sensor.

NOTICE: Make sure electrical connector remains securely fastened.

^ Refer to "MAP Output Check" in C CHARTS/ MANIFOLD ABSOLUTE PRESSURE (MAP) OUTPUT CHECK MAP Sensor Output Diagnosis for further diagnosis.