P0117 on Ford: How to Diagnose & Fix
Engine Coolant Temperature Sensor Circuit Low
2 Ford models · 2 documented issues · 2 critical · $400-$7,000 repair
P0117 on Ford by model: symptoms, diagnosis and fix
The 3.5L Duratec and 3.5L EcoBoost V6 engines in the Ford Flex have a critical design flaw: the water pump is driven by the timing chain and mounted internally inside the engine. When the water pump seal fails, coolant leaks directly into the engine oil, creating a milky sludge that destroys engine bearings in a matter of miles. Because the pump is internal, there is no external leak to warn the owner — the first symptom is often catastrophic engine failure. This is one of the most expensive and common failures on high-mileage Flex vehicles, with repair quotes ranging from $5,000 to $7,000+ for engine replacement.
Common Symptoms
- Milky or frothy substance on oil dipstick or under oil fill cap
- Sweet smell from engine oil indicating coolant contamination
- Coolant level dropping with no visible external leak
- Engine overheating
- Low oil pressure warning light
- Knocking or ticking sound from engine indicating bearing damage
- White or sweet-smelling exhaust
How to Fix
Proactively replace the water pump and timing chain as preventive maintenance between 100,000-120,000 miles ($1,500-$2,500 labor-intensive job). Check oil regularly for milky appearance or coolant smell — catching it early can save the engine. If coolant is found in the oil, stop driving immediately and have it towed. Use only Ford-approved coolant to minimize seal degradation. Consider extended warranty coverage when purchasing a high-mileage Flex.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Engine Water PumpCross-refWPFD-609V
Fitment confirmed against the ShowMeTheParts catalog for this vehicle's year and engine.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (1)
The 3.8L V6 intake manifold gaskets degrade and allow coolant to leak externally or internally into the engine oil. This is closely related to the head gasket issue and can lead to overheating and engine damage if not addressed.
Common Symptoms
- Coolant loss with no visible leak
- Milky oil
- Overheating
- Coolant smell from engine bay
How to Fix
Replace both upper and lower intake manifold gaskets. Use updated Fel-Pro gaskets. Flush the cooling system and change the oil if coolant contamination is found.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Engine Intake Manifold Gasket SetCross-refMIS16230-1
Fitment confirmed against the ShowMeTheParts catalog for this vehicle's year and engine.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (1)
P0117 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0117 mean on a Ford?
P0117 stands for "Engine Coolant Temperature Sensor Circuit Low." This code means the engine coolant temperature (ECT) sensor is reading too low a voltage, which the computer interprets as an impossibly high coolant temperature. In most cases this is an electrical fault — such as a short to ground in the wiring — rather than the engine actually overheating. The coolant temperature signal affects fuel mixture, cooling fans, and other functions, so a bad reading can cause poor running, hard starting, or fans running constantly. The fault is usually in the sensor or its wiring. On Ford it is documented across 2 models: Flex, Windstar.
What are the most common causes of P0117?
The most common causes of P0117 are: Faulty engine coolant temperature sensor, Short to ground in the sensor signal wire, Damaged or corroded wiring/connector at the sensor, Coolant contamination affecting the sensor, Poor electrical ground, Faulty PCM/ECM (less common). The specific cause varies by vehicle.
How much does it cost to fix P0117 on a Ford?
Published repair estimates on Ford range from $400 to $7,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0117 on a different make?
View P0117 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.