P1778

Symptoms

• Warning light with stored code
• harsh
• delayed
• or unpredictable shifting/ratio changes
• transmission slipping or stuck in one ratio
• poor throttle response
• harsh engagements from a stop
• inability to select certain ranges (R, D, N)
• limp mode
• possible stalling
• possible drive belt slippage and overheating.

Probable causes

• Faulty step motor (mechanical failure of the step motor is the documented trigger - pulley ratio not following TCM commands)
• damaged
• corroded
• or disconnected wiring/connectors in the step motor circuit
• low or contaminated/unsuitable CVT fluid
• defective ratio control valve
• pressure pump malfunction
• corrupted TCM programming. Nissan issued an extended warranty for many vehicles with this CVT.

Diagnostic steps

1. Connect a scan tool that communicates with the TCM, retrieve all stored codes and data.
2. Check CVT fluid level and condition; replace if low, dirty, or of the wrong specification (use the correct Nissan CVT fluid).
3. Inspect the wiring and connectors between the TCM and the step motor for damage, corrosion, or looseness, and repair as needed.
4. Clear the code and road test to see if P1778 returns.
5. If it returns, test the step motor circuit/function; replace the step motor if it is faulty.
6. Check for applicable Nissan TSBs and TCM reprogramming, and verify whether the vehicle falls under Nissan's extended CVT warranty before authorizing major repairs; persistent internal failures may require CVT overhaul or replacement.