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Circuit/System Testing

IMPORTANT: Diagnose any antilock brake system (ABS) related DTCs before performing this diagnostic.
  1. Ignition OFF, disconnect the X2 harness connector at the radio. Connect a DMM to the vehicle speed signal (VSS) circuit terminal E and ground.
  2. Ignition ON, operate the vehicle drive wheels at 5 mph. Verify 3-7 Hertz on the VSS circuit.
    • If the reading is not as specified, test the VSS circuit for an open, high resistance, short to ground or short to voltage. If the circuit tests normal replace the ECM.
  3. If the circuit tests normal, replace the radio.
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