P0351

Ignition coil A primary/secondary circuit fault.

The computer detected an electrical problem at the circuit that controls or monitors the coil identified as A. It doesn't confirm that the coil's damaged.

What should be checked

Primary or secondary ignition circuit to inspect

The module can detect an open circuit, abnormal current, or incorrect response in the circuit that drives and monitors an ignition coil.

In plain language: The electrical order to the identified coil may not be arriving or returning as the computer expects.

How to check it: Confirm which coil the letter identifies, inspect the connectors, and measure power and control with the correct diagram.
Before correcting it: Do not swap or replace ignition coils blindly, and do not bridge the circuit. The correction is decided only after locating and confirming the defect.
Related components: This diagnostic path may involve the ignition coil, connector, power, ground, wiring, spark plug, or control stage. None is confirmed.
When to stop: High voltage, a flashing warning light, or tests with the engine running require proper tools and training.

Power supply system to be checked

An insufficient or irregular ignition energy may prevent a stable combustion.

In plain language: The mixture may not be receiving a strong and stable spark.

How to check it: Confirm the engine and follow the authorised ignition sequence without blindly exchanging parts.
Before correcting it: The code does not authorize changing spark plugs, coils, cables or modules. The correction is decided only after locating and confirming the defect.
Related components: This path may involve spark plugs, ignition coils, high-tension leads if fitted, connectors, or wiring. None has been confirmed.
When to stop: High voltage and a running engine require proper tools and training.

Primary or secondary ignition circuit to inspect — The electrical order to the identified coil may not be arriving or returning as the computer expects.

Information needed for a more precise diagnosis

Exact brand, model, year, version and engine.
All the codes present and their OBD status.
Freeze frame and live data related to the system.
Symptoms, mileage and recent maintenance history.
Procedure and limits of an authorised source for that vehicle.

Where to find diagrams and manuals

Manufacturer repair information directory

Choose the make and open its official portal to find the manual, diagrams, cylinder arrangement, and bulletins for the exact vehicle.

Availability, registration, and cost depend on the manufacturer. The link does not grant permission to copy the manual.

Freedom to Fix: emissions service information

Understand which emissions-related service information manufacturers must make available for purchase.

Explains regulated access in the United States; it does not contain the vehicle-specific diagram or make the manual free.

Sources reviewed

Audi A8/A8L/S8 Quick Reference Specification Book — Audi of America / archivo NHTSA. It supports the punctual definition of the code; It does not identify a cause, a part or a repair.
Frequently Asked Questions About On-Board Diagnostics — U.S. Environmental Protection Agency. Supports the safety difference between a fixed breakdown lamp and a flashing lamp; It doesn't diagnose the cause.