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Home >> Buick >> 2008 >> Allure CXL >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 10 (Engine Control System & Fuel System - 5.3L - DTC P0420 To DTC P3449) >> DTC P0641 or P0651 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different variant/trim than selected.
IMPORTANT: A short to voltage on the signal circuit of certain components may cause this DTC to set.
  1. Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC. Refer to Diagnostic Aids  for appropriate sensors.
  2. Ignition ON, measure for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.
    • If less than the specified range, test for a short to ground on all the 5-volt reference circuits. If all circuits test normal, replace the ECM.
    • If greater than the specified range, test for a short to voltage on all of the 5-volt reference circuits. If all circuits test normal, replace the ECM.
  3. Connect each component associated with the 5-volt reference circuit, one at a time, while monitoring the voltage. Verify the voltage remains between 4.8-5.2 volts.
    • If not within the specified range when a component is connected, test the signal circuit for a short to voltage. If the circuit tests normal, replace the appropriate component.
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