GM CASE Relearn | Crankshaft Position Variation Learn Procedure

CASE stands for Crankshaft Angle Sensor Error. The relearn — GM calls it Crankshaft Position Variation Learn — measures the tiny machining variations in your reluctor wheel and stores them in the PCM, so the misfire monitor knows what a normal crank pulse train looks like on your engine instead of a generic one.

When you need one

• Any time you install a different PCM you intend to run long term — this includes every one of our core programs.
• After replacing the crankshaft position sensor, the reluctor wheel, the balancer, or the crankshaft itself.
• After an engine swap or a rebuild that changed the rotating assembly.

You do not need one for a tune-only change, and you do not need to repeat it if you swap back to your original PCM or disconnect the battery. Once it's stored, it's stored.

What happens if you skip it

The engine still runs. You'll set P0315 — Crankshaft Position System Variation Not Learned, and the PCM's misfire detection runs on default values, so it can throw false misfire codes or miss a real one. On anything that has to pass an emissions inspection, P0315 will fail you. Get it done within a couple of weeks of the install.

What it takes

Roughly five minutes and a scan tool that supports the function. Any of these will do it:

• Tech 2 or Tech2Win
• GM MDI 2 with GDS2
• HP Tuners MPVI2 / MPVI3 (Special Functions)
• Most mid-tier and up bidirectional scanners — Autel, Snap-on, Launch
• Some standalone gauges, depending on year: Aeroforce Interceptor, DashHawk

Any shop with a capable scanner can run it. Call around on price before you decide between our core program and the loaner program — it's a quick job and shops charge all over the map for it.

The procedure

The exact prompts vary by tool, but the drive cycle is the same on every Gen III and Gen IV GM.

1. Bring the engine to full operating temperature. The PCM will refuse to enter the learn below its coolant temperature threshold.
2. Find a safe stretch of road, or put the vehicle on a lift with the drive wheels free. You are going to hit fuel cutoff.
3. Connect the scan tool and select Crankshaft Position Variation Learn (some tools list it as CASE Learn or CKP Variation Learn).
4. Follow the tool's prompt to enable the learn. It will tell you when it's armed.
5. With the brake applied and the transmission in gear per the tool's instruction, accelerate at wide open throttle until the engine hits fuel cutoff — usually somewhere around 4,000–5,000 RPM. You'll feel it break.
6. Release the throttle completely and let the engine decelerate on its own. Do not touch the throttle during the coast down; the PCM takes its measurements here.
7. The tool reports the learn complete. If it reports incomplete, repeat from step 5 — two or three attempts is normal.
8. Clear P0315 and any codes set during the procedure.

If the learn won't complete

• Engine not fully warmed up, or coolant temperature sensor reading low.
• You lifted off before actual fuel cutoff, or feathered the throttle on the way down.
• Active misfire, cam or crank correlation code, or a rough-running condition — fix that first, the PCM won't learn through it.
• Reluctor wheel damage or a loose balancer. The variation is genuinely out of range.