Diagnostic Aids

The ECM supplies a 5 volt signal to pin C (circuit 474) of the Barometric Pressure (BARO) sensor and supplies a ground path to pin A (circuit 476-X). The BARO signal from pin B (circuit 433) is a variable voltage which is dependent on the barometric pressure.

Trouble Code 36 indicates that the voltage signal from the BARO sensor is too low. This situation can be observed in engine data display as a "BARO" reading (parameter .0.3) of 14 to 52 kPa. Possible causes of this condition are:

• A. A defective BARO sensor.
• B. Defective wiring, terminals, etc.
• C. An ECM which is unable to process signals properly.

1. If the opposite condition (high BARO signal) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter .0.3. With the opposite condition created parameter .0.3 should display a "BARO" reading of 106 to 108 kPa. To create a high BARO signal, disconnect the BARO sensor com1ector and jumper circuits 433 and 474 together. If the "BARO" reading is now 106 to 108 kPa the fault must be improper mating of sensor terminals or a faulty BARO sensor.
2. If the "BARO" reading is 105 kPa or less, measure the voltage on circuit 474. If the voltmeter reads 0 volts, then the BARO sensor is not receiving 5 volts and circuit 474 must be repaired for an open or short to ground.
3. If the voltmeter reads 5 volts, then measure the voltage between circuits 474 and 433. If the voltage is 5 volts, check circuit 433 for a short to ground. If the wiring is OK, then the fault must be in the ECM connector or ECM itself.
4. If the voltmeter does not read 5 volts, then an open must exist in either the wiring harness or the ECM. If the BARO reading is still 105 kPa or less with circuits 474 and 433 jumpered together at the ECM, the fault must be in the ECM connector or ECM itself. If the reading is 106 to 108 kPa, then circuit 433 is open.