Throttle Actuator Control Range/Performance (Volkswagen)
What does P1678 mean?
The P1678 code means the vehicle's onboard diagnostic system has detected: Throttle Actuator Control Range/Performance (Volkswagen). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Limp mode with limited throttle
- EPC warning light on
- Poor acceleration response
- Idle surging or fluctuation
Probable Causes (Ranked by Likelihood)
- Carbon buildup on throttle body plate Very High
- Faulty throttle body assembly High
- Throttle body not adapted after battery disconnect Moderate
- Damaged accelerator pedal position sensor Low
Step-by-Step Diagnostic Procedure
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Perform a throttle body adaptation reset using a VW/Audi diagnostic tool (VCDS or equivalent).
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Remove and inspect the throttle body for heavy carbon buildup on the butterfly plate and bore.
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Clean the throttle body with appropriate cleaner and re-adapt.
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Test accelerator pedal position sensor voltages at idle and full throttle for smooth voltage increase.
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If cleaning and adaptation do not resolve the issue, replace the throttle body assembly.
Frequently Asked Questions
What is throttle body adaptation?
VW/Audi electronic throttle bodies require a software adaptation that teaches the ECU the minimum and maximum throttle positions. This must be done after cleaning or replacing the throttle body.
Can I do the adaptation without a special tool?
On some models a basic adaptation can be done by turning the key on for 30 seconds. However, a proper adaptation with VCDS is recommended.
What is the EPC light?
EPC stands for Electronic Power Control. It indicates a throttle system problem. When on, the vehicle typically enters limp mode with reduced power.