2014 GMC Acadia - CEL and limp mode activated

Maintenance/Repairs
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1

Check engine light comes on. goes into limp mode.
Have replaced knock sensor.

2

If you post the check engine light codes someone here might be able to help you better. most Autoparts stores like Autozone will scan your car for free.

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Limp Mode - Symptoms, Causes & Diagnosis (4 Easy Fixes) (mechanicbase.com)

also, there is a recall on your vehicle that might be causing your problem.
It is something to look into.


October 1, 2014 NHTSA CAMPAIGN NUMBER: 14V614000
Contamination of the Chassis Electronic Module
If the module experiences an electrical short, the vehicle could stall, increasing the risk of a crash.

NHTSA Campaign Number: 14V614000

Manufacturer General Motors LLC

Components ELECTRICAL SYSTEM

Potential Number of Units Affected 106,307

Summary

General Motors LLC (GM) is recalling certain model year 2013-2014 Cadillac CTS, Escalade, Escalade ESV, Chevrolet Suburban, Tahoe, GMC Yukon, and Yukon XL, and 2014 Buick Enclave, Chevrolet Express, Impala, Silverado HD, Traverse, GMC Acadia, Savana, and Sierra HD vehicles. In the affected vehicles, the chassis electronic module may be internally contaminated, resulting in an electrical short.

Remedy

GM will notify owners, and dealers will replace the chassis electronic module, free of charge. The recall began on December 26, 2014. Owners may contact GM customer service at 1-800-521-7300 (Buick), 1-800-458-006 (Cadillac), 1-800-222-1020 (Chevrolet), and 1-800-462-8782 (GMC). GM’s number for this recall is 14515.

Notes

Owners may also contact the National Highway Traffic Safety Administration Vehicle Safety Hotline at 1-888-327-4236 (TTY 1-800-424-9153), or go to www.safercar.gov.

22 Affected Products

26 Associated Documents

Request Research (Services fees apply)

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I don’t think a faulty knock sensor would be a common cause for limp mode. The knock sensor allows the computer to advance the timing a little more than it otherwise would (with no knock sensor). So a faulty knock sensor might cause the ignition timing to be more retarded, and that would show up as perhaps some hesitation on accelerations, perhaps also making the engine run a little hotter and leaner. You might also hear a little “ping” noise from the engine, esp when going uphill, accelerating.

As posted above, the best way to address this is by asking your shop to read out the OBD II drivetrain codes. You are welcome to post them here for more ideas. Usually they start with the letter “P”.