Code
P1556
VW idle
Idle speed regulation lower limit exceeded
The idle controller cannot reach the lower limit (VW).
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Most likely causes
- Vacuum leak
- Dirty throttle body
- Faulty idle valve
Symptoms you may notice
- Low or hunting idle
- Stalling
- Check engine light
Checks to run
- Clean the throttle body
- Smoke-test the intake
- Test idle control
Tools you may need
Throttle cleaner
Smoke machine
Always diagnose before replacing. Codes share symptoms; confirm the cause with measurements before buying parts.