p0128
Moderate
RAM · Trucks
Coolant Thermostat Below Temp
Quick Answer
Error code P0128 on your RAM Trucks means: Coolant Thermostat Below Temp. This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Allow engine to warm up and verify temperature gauge reading
2
Scan for additional thermostat codes
3
Check coolant level and top off if low
4
Feel radiator hoses for temperature difference
5
Replace thermostat housing and thermostat if stuck
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 assembly
Thermostat housing gasket
Coolant
Radiator hose clamps
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