Rough Running GM Vehicle – UnderhoodService
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Diagnostics

Rough Running GM Vehicle

This condition may be caused by an internal circuit board fault within the throttle body.

Rough Running, Reduced Engine Power, Service Engine Soon (SES) Light On, P0123 AND P0222

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Models

2020-2021 Chevrolet Silverado 2500/3500 w/6.6L 

L8T engine

2020-2021 GMC Sierra 2500/3500 w/6.6L L8T engine

A vehicle may come into the shop with a rough idle and/or reduced engine power. Upon inspection, you may find the SES lamp is illuminated and DTC’s P0123 and P0222 may be active or stored history. This condition may be more noticeable in very cold climates. Note: This PI is only applicable to failures that have resulted from vehicles being exposed to extreme cold, -10 Fahrenheit.

Cause

This condition may be caused by an internal circuit board fault within the throttle body.

Correction

If you encounter a vehicle with the above concern, it will be necessary to replace the throttle body and add a ground wire following the steps outlined below. Reference the attached pictures showing ground wire location. 

FIGURE 1
FIGURE 2

Repair Procedure

  1. Replace throttle body following the service procedure as outlined in service information.
  2. Using two 8mm ring terminals and one 8-inch piece of 14-gauge wire to make a ground wire as shown in Figure 1.
  3. Remove the oil fill cap and beauty cover from rocker cover on left bank.
  4. Attach one end of the ground wire to the lower right throttle body fastener with the crimp side of the ring terminal facing toward the bolt head (#1 in Figure 2), then attach the other end of the ground wire to the rocker cover fastener with the crimp side of the ring terminal facing toward the bolt head (#2 in Figure 2).
  5. Ensure that ground wire is secure.
  6. Road-test vehicle to ensure repair procedure is complete and clear any DTCs.

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