Coolant Thermostat Below Regulating Temperature
The POWERSTROKE-P0128 (Power Stroke) diesel fault code means: Coolant Thermostat Below Regulating Temperature. This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- intermediate
- Estimated cost
- $150-$400
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Common Symptoms
- Slow warm-up
- Heater blows cool
- CEL
- Lower MPG in winter
Probable Causes (Ranked by Likelihood)
- Stuck-open thermostat(s) Very Likely
- Failed ECT sensor reading low Likely
Frequently Asked Questions
What is P0128 on a 6.7L Power Stroke (Scorpion)?
P0128 on a 6.7L Power Stroke (Scorpion) (2011-present) indicates: Coolant Thermostat Below Regulating Temperature. This is a known diagnostic trouble code on this engine family and typically points to the causes listed above.
Can I drive with P0128 on my Power Stroke?
Yes, you can generally drive with this code, but diagnose it soon to prevent further damage.
How much does it cost to fix P0128?
Repair cost is typically $150-$400 depending on the underlying cause and whether you DIY or use a shop. Diagnostic time alone runs $100-$180 at most independent diesel shops.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
Monitor ECT warm-up time; spec is <10 min.
Replace thermostats (6.7L has two stats).
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines P0128 as a generic OBD-II code)
P0128 on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown:
Commonly Affected Vehicles
- 2011-present Ford F-250 Super Duty 6.7L Power Stroke
- 2011-present Ford F-350 Super Duty 6.7L Power Stroke
- 2011-present Ford F-450/F-550 Super Duty 6.7L Power Stroke
- 2015-2019 Ford F-650/F-750 6.7L Power Stroke
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