Just did a coolant service on a 2023 Tucson Hybrid and stumbled onto something I haven’t seen anyone talk about: a hidden self-bleed/test routine that seems to cycle the electric water pump, 3-way valve, and radiator fans without a dealer scan tool. I was able to get heat back quickly and watched the reservoir burp multiple times while the valve clicked through positions. Super cool to see it work in real time.
Here’s what I noticed:
- With ignition on (not READY), the pump and fans cycled on/off in a pattern and the 3-way valve stepped through a few positions. Heater went from lukewarm to hot once the valve moved, and the reservoir level dropped a few times as air purged.
- The routine ran about 10-15 minutes before everything settled, then repeated in shorter bursts. I kept a smart charger on the 12V to be safe.
- I did separate services on both loops: engine loop and the power electronics/motor loop (two reservoirs). A vacuum fill pulled the engine loop down fine, but the PE loop didn’t respond unless I capped and pulled directly on its reservoir neck, so they’re definitely isolated.
Questions for anyone with access to Hyundai docs or who has tried this:
1) Is this an official air-bleed mode for the Tucson Hybrid/PHEV? If so, what’s the proper entry/exit sequence and run time? Any risks running it with ignition on vs READY? I avoided READY to keep the engine from firing.
2) Does the non-hybrid 2.5 have an equivalent pump/thermostat service mode without GDS? Or is the old-school warm-up/idle at 2-3k still the way to go?
3) For the hybrid: is there a way to command the heater/valves fully open during bleeding without a scan tool, or is max-temp/max-fan sufficient? It seemed like the 3-way valve position mattered a lot for getting trapped air out.
4) Coolant intervals: owner’s info is a bit vague for the PE loop. What are you all following for engine vs inverter/motor coolant change intervals, especially in hot climates or lots of short trips? Anyone sent samples for lab analysis to see additive depletion (silicates/phosphates) on the OE coolant?
5) Vacuum fill tips on these cars: have you found a reliable method to pull both loops without cross-contaminating or overdrawing from one reservoir? I had to treat them independently.
6) Any gotchas with bleeding that could aerate the hybrid drive unit or cavitate the PE pump if the level dips during the cycle? I kept topping to the HOT mark as it dropped, but curious if there’s a better sequence.
If this is a legit built-in service routine, it’s a game changer for DIY cooling system work on the Tucson Hybrid/PHEV. Would love to confirm the correct procedure, temperature targets, and any precautions (time limits, 12V support, cap on/off, etc.).