P0315: Crankshaft Position System Variation Not Learned
What Does P0315 Mean?
P0315 is a diagnostic trouble code indicating: Crankshaft Position System Variation Not Learned. This code relates to the ignition system system. It has been reported in NHTSA complaints across 2 different vehicle models.
Engine misfires are detected by monitoring crankshaft rotational speed variations. Each cylinder's power stroke produces a characteristic acceleration pattern. When a cylinder fails to fire, the crankshaft decelerates during that cylinder's stroke. The ECM identifies which cylinder misfired and how often. P0313-P0399 codes cover extended misfire monitoring including lean misfire detection, knock-related ignition faults, and secondary ignition monitoring. A flashing check engine light during active misfires is an emergency — raw unburned fuel enters the catalytic converter, potentially destroying it.
Symptoms of P0315
- ⚠️ Check engine light on (may flash during active misfire)
- ⚠️ Engine misfiring — rough idle, stumbling, shaking
- ⚠️ Loss of power during acceleration
- ⚠️ Increased emissions and fuel consumption
- ⚠️ Catalytic converter damage if ignored
- ⚠️ Possible engine vibration at idle
Common Causes
- 🔍 Worn or fouled spark plugs
- 🔍 Faulty ignition coil
- 🔍 Vacuum leak causing lean misfire
- 🔍 Fuel injector issue (clogged, leaking, or electrical)
- 🔍 Low compression (worn rings, burned valve, head gasket)
- 🔍 Incorrect ignition timing
P0315 Reports by Year
Real Owner Reports
From NHTSA complaint database — actual owner descriptions.
"CHECK ENGINE LIGHT ON WHILE ON HIGHWAY, AFTER GETTING OFF THERE WAS A VERY ROUGH IDLE. TOWED TO FRONTIER FORD IN SAN JOSE, CA. FOUND P0302, P0315 PCM. ENGINE MISFIRE. #2 CYLINDER WAS FOUND TO HAVE COOLANT INSIDE. A NEW ENGINE LOG BLOCK IS NEEDED TO CORRECT THIS CONCERN. THIS ENGINE CLEARLY HAS "
— Ford Fusion owner, 06/21/2020
"2011 FORD MUSTANG 3.7L V6 CONVERTIBLE, PREMIUM, AUTOMATIC TRANSMISSION THROTTLE BODY FAILURE (PART # AT4Z-9E926-B) WHILE DRIVING, THE CAR SUDDENLY DECELERATES, THE DASHBOARD 'WRENCH LIGHT' COMES ON, THE FRONT END OF THE CAR RUMBLES AND SHAKES, AND THE CAR WILL NOT ACCELERATE, FORCING ME TO PUL"
— Ford Mustang owner, 10/29/2019
Source: NHTSA Complaints Database
Most Reported Vehicles for P0315
Based on NHTSA owner complaint data.
| # | Vehicle | Reports |
|---|---|---|
| 1 | FORD FUSION | |
| 2 | FORD MUSTANG |
Diagnostic Tips
- Check misfire counters in Mode 6 data — identifies which cylinder(s) are misfiring most
- Swap ignition coil to another cylinder — if misfire follows, coil is bad
- Check spark plugs — worn electrode, fouled with oil or carbon, cracked insulator all cause misfires
- Perform compression test on affected cylinder(s) — low compression means mechanical issue
Common Mistakes to Avoid
- ❌ Replacing coils without checking spark plugs — a worn plug will kill a new coil
- ❌ Ignoring a flashing check engine light — this means severe misfire that's damaging the catalytic converter NOW
- ❌ Replacing ignition parts when the misfire is caused by a vacuum leak or low compression
Frequently Asked Questions
What does a flashing check engine light mean?
Can misfires damage my engine?
Why does my car misfire only when cold?
What To Do Next
Possible Fixes
- 🔧 Replace spark plugs
- 🔧 Replace ignition coil(s)
- 🔧 Repair vacuum leak
- 🔧 Clean or replace fuel injector
- 🔧 Engine mechanical repair (valves, rings, gasket)
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Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
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Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
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Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.