Definition GMC P1393
P1393 – Crankshaft Position System Variation Not Learned
The Engine Control Module (ECM) has not been able to record the variation values of the Crankshaft Position Sensor (CKP). This is necessary for optimal engine operation.
Possible Causes
- Learning Procedure Not Performed – The ECM needs to be recalibrated after certain repairs.
- Problem with the CKP Sensor – Failure, bad signal, or incorrect installation.
- Damaged Wiring or Faulty Connectors – Short circuit, corrosion, or poor contact.
- Mechanical Problem – Damaged teeth on the flywheel or reluctor ring.
- ECM Failure – Rare, but possible in case of software or hardware issues.
Common Symptoms
- Hard Starting (especially when hot)
- Unstable Idle or stalling
- Loss of Power and hesitant acceleration
- Malfunction Indicator Lamp (MIL) Illuminated
Diagnosis and Repair
1. Perform the CKP Learning Procedure
- Requires a compatible GM diagnostic tool (Tech2, Snap-On, Autel, etc.).
- The procedure varies by model (consult vehicle specifications).
2. Check the CKP Sensor
- Resistance Test (check specific values in the repair manual).
- Visual Inspection (cracks, damage, correct positioning).
3. Inspect Wiring and Connectors
- Check the wires between the CKP sensor and the ECM.
- Look for short circuits, breaks, or oxidation.
4. Examine the Flywheel/Reluctor Ring
- Check the condition of the teeth (no breaks or excessive wear).
5. Reset the ECM After Repair
- Clear the code and check if it returns after a drive cycle.
Affected GMC Models
This problem can occur on various models, including:
- GMC Sierra (1500, 2500, etc.)
- GMC Yukon / Yukon XL
- GMC Canyon
- GMC Acadia
- Other vehicles with GM engines (e.g., Vortec, EcoTec, etc.)
Important Note
- Some models require an advanced diagnostic tool to perform the CKP learning.
- If the code returns after repair, check:
✅ The CKP sensor supply voltage (typically 5V or 12V).
✅ The absence of mechanical issues (timing belt, synchronization).