P279A GMC - Four Wheel Drive High Range Performance

Repair Importance Level: 3/3
Repair Difficulty Level: 3/3   
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Possible causes

  • Faulty Engine Control Module (ECM)
  • Engine Control Module (ECM) harness is open or shorted
  • Engine Control Module (ECM) circuit poor electrical connection
  • Possible symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)
  • P279a Gmc Description

    The Engine Control Module (ECM) uses the following two ways to determine if the transfer case is in 4WD Low, 4WD High or Neutral.

    1. The first way is to compare the transmission output speed sensor to the transfer case output speed sensor in order to calculate transfer case range.

    2. The second way is to use a LAN message sent by the transfer case shift control module to the ECM.

    The ECM uses this message to determine motor torque required and transmission shifting.

    The internal fault detection is handled inside the control module. No external circuit diagnosis is involved.

    OBDII Code P279a Gmc - Four Wheel Drive High Range Performance - AutoCodes.com

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