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Home >> Buick >> 2007 >> Lucerne CX >> Repair and Diagnosis >> External Pages >> Different car >> Section 150 (Engine Control System - 3.6L (Ly7) - DTC P0442 To DTC P1551) >> DTC P0685, P0686, P0687, P0689 or P0690 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the EC ignition or PT relay.
  2. In order to load the circuit, connect a test lamp between the B+ supply circuit to the coil side of the PT relay and the negative terminal of the battery.
  3. Ignition ON, test for less than 0.1 volts between the B+ voltage circuit of the PT relay and the positive battery terminal.
    • If greater than 0.1 volts, repair the B+ voltage circuit to the coil side of the PT relay for a short to ground or an open/high resistance.
  4. In order to load the circuit, connect a test lamp between the B+ voltage supply circuit to the switch side of the PT relay and the negative terminal of the battery.
  5. Ignition ON, test for less than 0.1 volts between the B+ voltage circuit of the PT relay and the positive battery terminal.
    • If greater than 0.1 volts, repair the B+ voltage circuit to the switch side of the PT relay for a short to ground or an open/high resistance.
  6. With the ignition OFF, connect a test lamp between the control circuit of the PT relay and the B+ voltage supply circuit to the coil side of the PT relay.
  7. Turn ON the ignition. The test lamp should turn ON when the ignition switch is cycled ON and OFF when the ignition switch is cycled OFF.
    • If the test lamp remains ON all the time, test for a short to ground on the control circuit. If the circuit/connections test normal, replace the ECM.
    • If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the control circuit. If circuit/connections test normal, replace the ECM.
    8. IMPORTANT: The ignition 1 voltage circuit is between the PT relay and the ECM. The ignition 1 voltage is a feedback circuit.
  8. Connect a 15-amp fused jumper wire between the B+ supply voltage circuit and the ignition 1 voltage circuit of the PT relay.
  9. Attempt to start the engine. The engine should start.
    • If the engine does not start, test the ignition 1 voltage circuit between the PT relay and the ECM for a short to ground or for an open/high resistance. If the circuit/connections test normal, replace the ECM.
  10. If all circuits/connections test normal, test or replace the PT relay.
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