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P0315 — Crankshaft Position System Variation Not Learned

Generic OBD-II · all makesPowertrain (engine & transmission)

OBD-II code P0315 indicates that the engine control module (PCM) has not learned the crankshaft position sensor's signal variation. This learned value is essential for accurate misfire detection and ignition timing. The code often appears after a crankshaft position sensor replacement, PCM replacement, or battery disconnect without performing the required relearn procedure.

Symptoms

What causes it — most likely first

1. Crankshaft position system variation not learned

The most common cause is that the crankshaft position system variation learn procedure has not been performed after a repair or battery disconnect. The PCM requires this relearn to accurately detect misfires.

2. Faulty crankshaft position sensor

A failing or contaminated sensor can provide erratic signals, preventing the PCM from completing the learn procedure or causing the code to set.

3. Damaged or contaminated reluctor ring

The reluctor ring on the crankshaft may have missing teeth, cracks, or debris, leading to an inconsistent signal that the PCM cannot learn.

4. Wiring or connector issues

Corroded, loose, or damaged wiring and connectors between the crankshaft position sensor and the PCM can disrupt the signal, causing the learn procedure to fail.

5. Incorrect sensor gap or mounting

If the sensor is not installed with the correct air gap or is misaligned, the signal may be too weak or distorted for the PCM to learn the variation.

6. PCM failure (rare)

In very rare cases, an internal fault in the PCM can prevent it from storing the learned variation. This should only be considered after all other causes are ruled out.

How it's diagnosed

  1. Verify the code with a scan tool and check for any other related codes (e.g., P0335, P0336). Clear codes and see if P0315 returns immediately.
  2. Perform the crankshaft position system variation learn procedure using a scan tool capable of initiating the relearn. Follow the vehicle manufacturer's specific instructions (often requires holding engine RPM at a certain range).
  3. Inspect the crankshaft position sensor and its connector for damage, corrosion, or loose fit. Check the sensor's resistance and output signal with a multimeter or oscilloscope if the relearn fails.
  4. Examine the reluctor ring for damage or debris by removing the sensor and visually inspecting through the mounting hole, or using a borescope. Check for excessive crankshaft end play that could affect the signal.
  5. Test the wiring harness between the sensor and PCM for continuity, shorts to ground, or shorts to voltage. Repair any faults found.
  6. If all else is normal and the relearn repeatedly fails, suspect a PCM fault. Before replacement, verify PCM power and ground circuits, and check for software updates from the manufacturer.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationSAE generic — identical on every make
Related codesP0310 — Cylinder 10 Misfire DetectedP0311 — Cylinder 11 Misfire DetectedP0312 — Cylinder 12 Misfire DetectedP0313 — Misfire Detected Low FuelP0314 — Single Cylinder Misfire Cylinder Not SP0316 — Engine Misfire Detected Startup First

Frequently asked

Can I drive with a P0315 code?

It may be possible to drive, but the engine could run poorly, stall, or fail to start. The PCM cannot accurately detect misfires, which may lead to undiagnosed engine damage. It is best to address the code promptly.

Do I need to replace the crankshaft position sensor?

Not necessarily. The code often sets because the relearn procedure was not performed after a repair or battery disconnect. Try the relearn first. Replace the sensor only if it fails testing or the relearn cannot be completed after ruling out other causes.

Is the PCM the most likely cause of P0315?

No. Despite some advice, the PCM is very rarely at fault. The overwhelming majority of cases are resolved by performing the crankshaft variation learn procedure or repairing a sensor/wiring issue. PCM replacement should be a last resort after thorough diagnosis.

How do I perform the crankshaft position system variation learn?

The procedure requires a professional-grade scan tool that can command the PCM to enter learn mode. Typically, the engine is warmed up, then the scan tool initiates the learn while the engine is held at a specified RPM (often around 4,000 RPM) until the PCM confirms completion. Refer to the vehicle service manual for exact steps.