Having problems with your 1999 GMC Sonoma ?
99' GMC Sonoma. The heater quit heating completely about a week ago. I flushed the system and added fresh coolant and even disconnected the lines at the firewall and applied air pressure to blow out any clogs that might be in the core. The coolant runs through perfectly free and the heater now gets warm. Can't find any leaks, but it still doesn't get as hot as it used to. The only other thing I see, is that it takes a few seconds now for the air flow to change from the upper vents, to the floor,
Repair Help & Product Troubleshooting for 1999 GMC Sonoma
Tips for a great answer:- Provide details, support with references or personal experience .
- If you need clarification, ask it in the comment box .
- It's 100% free, no registration required.