P0300 Code Ford Fusion: Random Misfire Causes & Fixes

Verifying a Fusion misfire repair

Write down the freeze frame and all cylinder counters before clearing anything. Those numbers are your only record of the conditions that produced the misfire, and you need them to prove the repair worked.

After the repair, drive the load, rpm and temperature conditions the freeze frame recorded and confirm the counters stay at zero across all of them. A lamp that stays off during a short idle proves nothing about a misfire that appeared under load.

On a 1.5L or 2.0L EcoBoost, check the coolant level again a week later even if the misfire is gone. Coolant intrusion can be slow and intermittent in its early stages, and a level that has dropped again while the car appears to run fine is telling you something important while it is still cheap to act on.

What can set P0300—and how to separate it

The order below is evidence-driven, not a universal probability ranking. Vehicle year, repair history, companion codes and the operating condition in freeze frame change where diagnosis should begin.

The coolant-intrusion test, and why it takes five hours

If you have a 1.5L or 2.0L EcoBoost Fusion with misfire and coolant loss, this is the single most useful section on the page — because it describes a specific, published test rather than a general suspicion.

The failure itself is a crack forming in the narrow, unsupported casting between cylinders on these open-deck blocks. Coolant escapes into the combustion chamber, which produces the misfire, the white smoke, the stalling and the limp mode. It is not a head-gasket failure in the conventional sense and it does not always show on a quick pressure check, because the leak can be slow.

Ford's diagnostic route for the 2.0L, published in TSB 19-2346, is deliberately patient. The cooling system is pressurised to 138 kPa — 20 psi — and held for five hours. If pressure has dropped by 27.57 kPa (4 psi) over that period, and a borescope inspection confirms coolant inside the cylinders, the remedy is short-block replacement.

That five-hour hold is the part people skip. A ten-minute pressure test can pass an engine that is genuinely losing coolant internally, which is exactly how these get misdiagnosed as ignition faults. If a shop tells you the cooling system holds pressure, ask how long they held it for.

What the repair actually involves

Where coolant intrusion is confirmed, the Ford-recommended repair is an engine long-block assembly. There is one detail worth knowing that saves money: Ford has found that returned 1.5L cylinder heads pass inspection, so the original head can be reused rather than replaced.

If someone quotes you for a complete engine including a new head on a 1.5L, that is worth questioning against the published guidance. The block is the part that cracked; the head generally is not.

It is also worth checking coverage before paying. Ford addressed this through service bulletins rather than a formal recall, but bulletin coverage, extended warranty programmes and ongoing legal action have all applied to various model years. Check your VIN through a dealer and through the NHTSA database before assuming the bill is entirely yours.

The cheaper 1.5L possibility worth ruling out first

Before you conclude a 1.5L Fusion needs a short block, check one much smaller thing. Ford TSB 16-0150 covers some 2014–2017 Fusion vehicles with the 1.5L GTDI engine where an intake manifold bolt backs out and damages the charge air cooler.

The symptoms it lists overlap almost exactly with the ones that frighten people into expecting the worst: low coolant, white exhaust smoke and an illuminated lamp. The remedy, however, is nothing like a short block.

So on a 1.5L with coolant loss and misfire, checking bulletin coverage costs you nothing and can change the outcome by thousands. Do that before authorising major work.

2.5L, 2.0L Hybrid and the ordinary causes

• The 2.5L Duratec and the 2.0L Atkinson hybrid are not part of the coolant-intrusion pattern
• On those engines work plugs, coils, vacuum leaks and fuel delivery in that order
• Start with the plugs — cheapest to inspect and they frequently show the answer outright
• Use the free coil swap before buying anything: move a coil, clear the code, see if the misfire follows
• On the hybrid, allow for the engine cycling on and off; live data needs a continuous run to be readable
• Check the coolant level anyway — it costs nothing and rules out the expensive scenario

Save these scan-data clues

Freeze frame is a snapshot of conditions when the PCM matured the fault. It can distinguish an idle-only problem from a load, cold-start or monitor-completion problem. Clearing first throws that context away.

• Individual cylinder misfire counters — P0301 through P0304 alongside P0300 narrows things considerably
• Engine coolant temperature, separating a cold-start fault from a fully warm one
• Short and long-term fuel trim; positive trims alongside misfire point at a lean condition as the cause
• Engine load and rpm, distinguishing idle misfire from load misfire
• Any companion codes — lean codes, a cooling-related code or a boost code redirect the diagnosis
• Whether the engine stalled or entered limp mode at the same moment

A practical diagnostic workflow

1. 01
   Check coolant level and look for white smoke

   On a 1.5L or 2.0L EcoBoost this comes before everything else. Coolant loss with no puddle, white exhaust smoke or a sweet smell means you are potentially dealing with coolant intrusion rather than an ignition fault.

2. 02
   Save the freeze frame and cylinder counters

   Record misfire counts for every cylinder before clearing anything. If one cylinder dominates, the search area shrinks dramatically. If several climb together, that pattern matters too.

3. 03
   Pressure-test the cooling system properly

   Not for ten minutes. Ford's route for the 2.0L specifies 138 kPa (20 psi) held for five hours, with a 4 psi drop over that period indicating a problem. A short test can pass an engine that is genuinely leaking internally.

4. 04
   Borescope the cylinders if pressure drops

   The pressure drop tells you coolant is going somewhere. The borescope confirms it is going into the cylinders, which is what distinguishes coolant intrusion from an external leak you have not found yet.

5. 05
   Check bulletin coverage on a 1.5L

   TSB 16-0150 covers a backed-out intake manifold bolt damaging the charge air cooler on some 2014–2017 vehicles, with symptoms that look alarmingly similar. The remedy is far smaller. Check before authorising major work.

6. 06
   Inspect the spark plugs and compare them

   Lay them out in cylinder order. Deposits narrow the cause — sooty for rich, wet for no ignition, oily for oil intrusion. Coolant deposits look different again and point straight back to the cooling system.

7. 07
   Swap a coil rather than replacing several

   Move a coil from a misfiring cylinder to a healthy one, label both, clear the code and drive the conditions from your freeze frame. If the misfire follows the coil you have found it for free.

8. 08
   Smoke-test for vacuum leaks

   If fuel trims are positive alongside the misfire, the lean condition is likely the cause rather than a coincidence. On an EcoBoost, add a charge-air pressure test since a boost leak will not show at idle.

Ford service bulletins that name P0300

A bulletin does not automatically apply to your truck. Check the exact model year, engine and build date it covers, and have a dealer or shop confirm whether your VIN is included before paying for the work it describes.

P0300 repair cost comparison

These are planning ranges gathered from public U.S. estimate data, not quotations. Your figure moves with local labour rates, model year, engine and whether the shop bills diagnosis separately. Use them to judge whether a quote is reasonable — not to decide what is wrong.

Why the model year changes the test

Almost every Fusion engine is an inline four, so Bank 1 is the whole engine and there is no second bank to compare against. The exception is the 2.7L EcoBoost V6 fitted to the Sport from 2017, and the older 3.0L and 3.5L V6s, where Bank 1 and Bank 2 are genuinely separate. More importantly for several codes on this site: the 1.5L and 2.0L EcoBoost engines have a documented coolant-intrusion problem, and Ford publishes a specific test to confirm it.

• The 2014–2019 Fusion with the 1.5L EcoBoost is known for coolant consumption and white exhaust smoke caused by a crack in the unsupported casting between cylinders on the open-deck block.
• Ford addressed the 2.0L EcoBoost version of this problem through TSB 19-2346 rather than a formal recall, with a specified pressure test and short-block replacement as the remedy.
• Ford reports that returned 1.5L cylinder heads pass inspection, so the original head can generally be reused in the repair rather than replaced.
• The 2.5L Duratec and the 2.0L Atkinson hybrid are not part of this pattern and respond to conventional misfire diagnosis.