Circuit/System Testing

WARNING: This page is about a different car, the 2021 GMC Sierra 3500 HD and 2021 GMC Sierra 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.

NOTE:

This diagnostic procedure will only diagnose factory installed components. It will not diagnose upfitter provided equipment. If the cover for the frame rail X176 Provisional connector, which includes a jumper wire, is removed DTC P251E may set.

Ignition OFF and all vehicle systems OFF, disconnect the harness connectors at the K44 Power Take - Off Control Module and connector X3 at the K20 Engine Control Module. Remove the frame rail X176 Provisional connector cover. It may take up to 2 min for all vehicle systems to power down.
Test for less than 1 V between the K44 Power Take - Off Control Module connector X2 terminal 28 and ground.
- If 1 V or greater
  Repair the short to voltage on the circuit.
- Go to next step: If less than 1 V
Test for infinite resistance between the K44 Power Take - Off Control Module connector X2 terminal 28 circuit and ground.
- If less than infinite resistance
  Repair the short to ground on the circuit.
- Go to next step: If less than 2 Ω
Test for less than 2 Ω end to end at the K44 Power Take - Off Control Module terminals listed below:
- K20 Engine Control Module connector X1 terminal 25.
- K44 Power Take - Off Control Module connector X2 terminal 28.
- If 2 Ω or greater
  Repair the open/high resistance in the circuit.
- Go to next step: If less than 2 Ω
Test or replace the K20 Engine Control Module.
Verify DTC P159C does not set when operating the vehicle within the conditions for running the DTC.
- If the DTC sets
  Replace the K44 Power Take-Off Control Module.
- Go to next step: If the DTC does not set
All OK.