p0128
Moderate
Hyundai · Sedans
Coolant Thermostat Malfunction - Below Temperature
Quick Answer
Error code P0128 on your Hyundai Sedans means: Coolant Thermostat Malfunction - Below Temperature. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Accent SE 2022Azera Limited 2022Elantra SEL 2024Elantra Hybrid SEL 2024Elantra N 2024Elantra Limited 2024Elantra N Line 2024Elantra SE 2024Ioniq 6 Limited 2024Ioniq 6 SE Long Range 2024Ioniq 6 SE Standard Range 2024Ioniq 6 SEL 2024Sonata Limited 2024Sonata N Line 2024Sonata SE 2024Sonata SEL Plus 2024Ioniq 6 SE 2024Ioniq Hybrid Blue 2022Sonata SEL 2024Sonata Hybrid SEL 2024
Likely Causes
How to Fix It
1
Connect OBD-II scanner to read P0128
2
Check coolant level and top off if needed
3
Monitor coolant temperature during warm-up
4
Replace thermostat if stuck open
5
Test coolant temperature sensor resistance
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Thermostat
Coolant
Coolant temperature sensor
Water pump (if needed)
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