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Home >> Buick >> 2007 >> Allure CX >> Repair and Diagnosis >> External Pages >> Different car >> Section 68 (Engine Control System & Fuel System - 3.6L - DTC P0335 To DTC P2097) >> DTC P0685, P0686, P0687, P0689, or P0690 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the PT relay.
  2. Ignition ON, load test for B+ between both of the PT relay circuit terminals C5, C6, and ground.
    • If less than the specified range, repair the appropriate circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect a test lamp between the control circuit terminal A6 of the PT relay and B+. Verify the test lamp does not illuminate.
    • If the test lamp illuminates, test for a short to ground on the control circuit. If the circuit/connections test normal, replace the ECM.
  4. Ignition ON. Verify the test lamp illuminates when the ignition switch is cycled ON.
    • 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.
    5. IMPORTANT: The ignition 1 voltage circuit is between the PT relay and the ECM. The ignition 1 voltage is a feedback circuit.
  5. Connect a 15A fused jumper wire between the B+ supply voltage circuit terminal C6, and the ignition 1 voltage circuit terminal A5, of the PT relay.
  6. 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.
  7. If all circuits/connections test normal, test or replace the PT relay.
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