# 2003 GMC Yukon - Low Power Mode, Service 4ws, Service Brake

**URL:** <https://community.cartalk.com/t/2003-gmc-yukon-low-power-mode-service-4ws-service-brake/151905>\
**Category:** Maintenance/Repairs\
**Created:** [November 1, 2019, 1:20am UTC](https://community.cartalk.com/t/2003-gmc-yukon-low-power-mode-service-4ws-service-brake/151905 "2019-11-01T01:20:13Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![lowel](https://avatars.discourse-cdn.com/v4/letter/l/5e9695/32.png) [@lowel](https://community.cartalk.com/u/lowel)\
**Post date:** [November 1, 2019, 1:20am UTC](https://community.cartalk.com/t/2003-gmc-yukon-low-power-mode-service-4ws-service-brake/151905/1 "2019-11-01T01:20:13Z")

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lo power mode dtc code p1518 service 4wd servicebrake system all show up on any bump

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**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\
**Post date:** [November 1, 2019, 1:33pm UTC](https://community.cartalk.com/t/2003-gmc-yukon-low-power-mode-service-4ws-service-brake/151905/3 "2019-11-01T13:33:07Z")

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3 distinctly different problems needing repair…

Bad throttle body actuator, likely a bad 4WD switch and low brake fluid, maybe.

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**Author:** ![Scrapyard-John](https://avatars.discourse-cdn.com/v4/letter/s/f6c823/32.png) [@Scrapyard-John](https://community.cartalk.com/u/Scrapyard-John)\
**Post date:** [November 1, 2019, 4:06pm UTC](https://community.cartalk.com/t/2003-gmc-yukon-low-power-mode-service-4ws-service-brake/151905/4 "2019-11-01T16:06:05Z")

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Since all of these warnings appear whenever you hit a bump, I wonder if a connection in the wiring harness could be loose? Just a thought…