P3400

What it means

On Audi, P3400 means the engine control unit has detected a fault in the cylinder deactivation system, which shuts down some cylinders at light load to save fuel. The control unit saw that the deactivation or reactivation did not happen as commanded, or that an actuator circuit or feedback reading was outside its expected range. The exact hardware and which cylinders are affected depend on the engine, so confirm against model-specific data.

Symptoms

• Engine warning light on
• Cylinder deactivation no longer operates, so fuel economy gets worse
• Rough running or a noticeable shudder when the system switches mode
• Reduced power or the engine running in a fallback mode
• Ticking or tapping noise from the valve gear area
• Other stored codes for camshaft position or actuator circuits

Possible causes

• Faulty or sticking deactivation actuator (solenoid and pin) on the valve gearlikely
• Wiring damage or poor connector contact at the actuator circuitlikely
• Low, degraded or incorrect-specification engine oil affecting oil-pressure-operated or actuator componentslikely
• Worn or jammed sliding cam piece or valve lift mechanismpossible
• Camshaft position sensor or timing fault giving implausible feedbackpossible
• Outdated engine control unit software where a manufacturer update is known to address the faultrare
• Internal engine control unit driver faultrare

How to diagnose

1. Read all stored codes and freeze frame data, noting engine load, speed, temperature and oil temperature when the fault set
2. Check engine oil level, condition and that it matches the specification for the engine
3. Inspect the actuator wiring and connectors for damage, oil contamination, corrosion or loose pins
4. Check live data for cylinder deactivation status and camshaft position values to see whether the system responds to commands
5. Test actuator circuit resistance, supply and control signals against workshop data for the specific engine
6. Check for related camshaft sensor or timing codes and deal with those first
7. Inspect the valve gear for actuator pin movement and cam piece wear, following model-specific procedures
8. Check for applicable technical bulletins or software updates for the vehicle

How to fix

• Repair or replace damaged wiring and clean or renew faulty connectors
• Replace the faulty actuator and check the matching cam piece
• Correct the oil level and change oil and filter to the correct specification if it is degraded or wrong
• Replace worn or jammed valve lift components as found on inspection
• Replace a faulty camshaft position sensor or correct the timing fault
• Apply an official software update if a known calibration fault applies to the vehicle

Can I keep driving?

This code for other makes

• P3400GenericP34C8

Nearby codes

• P3100AudiHigh voltage powertrain control module failure
• P3401AudiEngine oil level is too low, Powertrain Control Module (PCM) failure, Variable valve timing solenoid failure, Wiring issue