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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 81 (Engine Controls - Self-Diagnostics - 8.1L) >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit >> Test Description

Test Description

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The numbers below refer to the step number in the diagnostic procedures.

  1. 2

    The 5-volt reference circuits for the sensors are connected together inside the PCM. Both DTCs P1635 and P1639 set at the same time, indicates a 5-volt reference circuit is shorted to a voltage.

  2. 3

    The 5-volt reference circuits for the sensors are connected together inside the PCM. When only DTC P1639 is set, this indicates a short to ground on one of the 5-volt reference circuits.

  3. 5

    This step determines if a 5-volt reference circuit is shorted to ground.

  4. 6

    The 5-volt reference circuits may be shorted to another PCM circuit. The shorted circuit may not be apparent when the PCM harness connector is disconnected. Testing continuity from each 5-volt reference circuit isolates the shorted circuit.

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