OBD-II trouble code
P0315: Crankshaft Position System Variation Not Learned
A calibration step has not been completed. Nothing on the car is necessarily broken, no part will fix it, and the usual repair is a scan tool procedure performed under specific conditions.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $75 – $900
- DIY difficulty
- Intermediate DIY
What does P0315 mean?
Misfire detection works by measuring how much the crankshaft accelerates on each power stroke, which means it depends on measuring crankshaft speed to a precision far finer than the manufacturing tolerance of the reluctor wheel the sensor reads. Tooth spacing on that wheel is never perfect. If the module simply took the raw readings at face value, a tooth two thousandths of an inch wide of nominal would look identical to a cylinder that produced slightly less torque than its neighbours.
The fix is a stored correction table. During a controlled deceleration with the fuel injectors switched off, no cylinder is contributing anything, so every variation the sensor reports must be mechanical. The module records that pattern and subtracts it from every subsequent measurement. P0315 means that table is absent, incomplete, or no longer valid for the hardware currently fitted.
The important consequence is that the misfire monitor cannot run without it. A vehicle carrying P0315 may be misfiring badly and setting no misfire code at all, because the diagnostic that would detect one has been disabled by the missing calibration. It also means the misfire readiness monitor will never set to complete, so the vehicle fails an OBD-II inspection on readiness even where the inspector never looks at the code list.
This code is almost always self-inflicted in the honest sense — it follows work rather than wear. Replacing a crankshaft position sensor, an engine controller, a harmonic balancer, a flywheel or flexplate, or performing timing work all change the relationship the stored table described. On some platforms an extended battery disconnect that clears keep-alive memory is enough. What it very rarely follows is nothing at all, so if P0315 appears on a vehicle with no service history behind it, look for a mechanical reason the reluctor pattern changed: a cracked or slipped balancer, a loose flexplate, or debris on the wheel.
The relearn itself is where people get stuck. It is not a code clear and it is not a battery disconnect. It is an OEM routine requiring a scan tool with the right capability, and it will refuse to complete unless the engine is within a specified coolant temperature band and the vehicle can be driven through a deceleration from a given speed with the throttle fully closed. Attempting it on a cold engine, or on a road where you cannot hold a closed-throttle decel, is the usual reason a technically correct procedure appears to fail.
Common causes
- Crankshaft position sensor replaced without performing the relearn afterwards
- Engine control module replaced, reprogrammed or reflashed
- Harmonic balancer, flywheel or flexplate replaced, changing the reluctor pattern
- Timing chain, belt or camshaft work altering the crank-to-cam relationship
- Keep-alive memory lost through an extended battery disconnect or a flat battery
- Relearn attempted but aborted because conditions were never met
- Cracked, slipped or damaged reluctor wheel making a valid learn impossible
- Crankshaft position sensor signal quality too poor for the procedure to complete
Symptoms
- Check engine light on with no driveability complaint at all
- Misfire readiness monitor permanently incomplete
- No misfire codes set even when the engine is obviously running unevenly
- Code returns immediately after being cleared with a scan tool
- Emissions inspection failure on monitor readiness rather than on a stored code
- In some cases a brief stumble or extended crank if the underlying signal is also degraded
Diagnostic steps
- 1.Establish what was done to the vehicle recently. Crank sensor, controller, balancer, flexplate or timing work makes this an unfinished job rather than a fault, and the answer is the procedure.
- 2.Confirm that no crankshaft or camshaft position circuit codes are stored. The relearn will not complete over a bad signal, and clearing those first is a prerequisite rather than an option.
- 3.Check the vehicle's specific relearn requirements before attempting it. Coolant temperature windows, a minimum starting road speed and a closed-throttle deceleration to a specified speed are typical, and they vary by manufacturer and model year.
- 4.Clear all stored codes immediately before running the procedure. Many implementations abort if any code is present when the routine starts.
- 5.Run the relearn with a scan tool that supports it. Generic code readers cannot perform this function no matter how many times codes are cleared.
- 6.If the procedure aborts repeatedly, inspect the reluctor wheel and the harmonic balancer for cracks, movement or debris, and check the crank sensor air gap and mounting.
- 7.After a successful learn, verify the misfire readiness monitor changes to complete over a normal drive cycle. That, rather than the absence of the light, is proof the fix took.
Repair cost
$75 – $900
When nothing is broken the whole repair is labour: most shops charge $75 to $200 to perform the crankshaft variation relearn, often folded into the cost of whatever job left it undone. If the relearn cannot complete because the sensor signal is poor, a crankshaft position sensor is $150 to $450 fitted plus the relearn afterwards. A cracked or slipped harmonic balancer is the expensive case at $350 to $900. Buying a generic code reader will not help — the routine requires a tool with bidirectional OEM capability.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with crankshaft position sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.