Diagnostic Aids
NOTE:
The following procedure is designed to account for intermittent codes. If no malfunction is uncovered using this procedure, it will indicate that the DFI system is OK at this time. Refer to NOTE ON INTERMITTENTS if further investigation is necessary.
Code 33 indicates that the ECM has seen a condition where the Manifold Absolute Pressure (MAP) sensor signal and the Barometric Pressure (BARO) sensor signal should have been the same voltage but were not (ignition on but the engine not running or cranking). Possible causes of this condition are:
- A. A faulty MAP sensor.
- B. A faulty BARO sensor.
- C. Defective wires, terminals, etc.
- D. An ECM not processing the signals properly.
- Begin diagnosis by determining whether the code is hard, intermittent or a sensor response problem. If after 10 seconds at ignition on, the code does not set either as a hard code or an intermittent, then the malfunction s not present at this time.
- If Code 33 is stored as a hard code after 10 seconds at ignition on, then this condition can be verified by displaying engine data parameters .0.2 and .0.3. The two pressure readings will differ by 2 or more kPa at ignition on. This could be caused by an open in one of the sensor ground circuits. If one of the sensor readings moves closer to the other when the ground circuits (476-X and 476-Y) are jumpered together, then the circuit to the sensor which changed in value is open.
- If neither reading moved, one of the sensors is faulty. To determine which sensor to replace, obtain a replacement MAP or BARO sensor and connect it to the appropriate harness connector. Compare this sensor's parameter value to those recorded previously. If the new sensor reads closer to the original reading for the BARO sensor, replace the MAP sensor. If the new sensor reads closer to the MAP sensor, replace the BARO sensor.
- If Code 33 was stored as an intermittent after 10 seconds at ignition on, one of the sensor's may be responding too slowly when power is applied. To determine if this is the case, observe each sensor's parametric value as the sensor is reconnected. A good sensor should go to its maximum value without displaying more than one intermediate value. If several values are displayed before the maximum, replace the affected sensor. If both respond properly, the ECM may not be processing the signals properly.