Heater Control Problem E70 3.0

[lt2mc]

Hey All, Did a lot of searching to get ideas on what may be causing a heater issue I was having. Most of the posts were for heater problems with only a few fixes posted. So I am starting a short thread for a heater fix I just did... and to brag a little.

Symptom; Minimal heat through all vents at any fan speed (except rear foot vents, which are electric heaters). After approximately 20 minutes of driving the system would produce some heat, but cool back down when fans were turned to high. Auto heat control did not function at all.

Possible Causes; Based on online research, possible causes, bad thermostat, failing water pump, bad heater valve, flackey sensors, etc...

Diagnostics; 1, Accessed the hidden OBC menus, and verified the thermostat/cooling system were working properly by watch the engine temp (07.00 KTMP) cycled between 98-105c during normal driving. 2, inspected the heater valve and determined all three lines were the same temp, though not too hot to hold. Suspected bad water flow through the heater core. 3, inspected coolant level, low but not too bad.

Repair; Performed the coolant auto bleed cycle while topping off the coolant, then repeated the auto bleed cycle. First cycle saw a lot of air being spit out of the system, second cycle showed a more solid stream.

Test; Closed up the system and let the engine idle for about 5 minutes while watching the KTMP display. Auto heating kicked on at about 58c, and the vehicle heated up to 70f within 5 minutes of that. Test drove the vehicle to verify the thermostat still cycled between 98-105c. All was normal.

Conclusion; She is all better now. all said and done three days of diagnostics, 30 minutes of work, and best of all no money spent.