P0400moderate severityPowertrain
Exhaust Gas Recirculation (EGR) Flow
on 2012 Audi A6 3.0L Supercharged V6 · AWD
What this code means
The EGR system flow is not within expected parameters.
Symptoms
- Check Engine Light
- Rough idle
- Pinging/knocking
- Increased NOx emissions
- Failed emissions test
Common causes
- Clogged EGR passages
- Faulty EGR valve
- EGR valve stuck closed
- Carbon buildup
- Vacuum line issue
Diagnostic steps
- Test EGR valve operation
- Check EGR passages for carbon buildup
- Test vacuum supply to EGR valve
- Monitor EGR position with scan tool
- Inspect EGR tube
Repair notes
Clean EGR valve and passages. Replace EGR valve if stuck or faulty.
🔌 Don't have a code reader?
Any of these will read and clear this code — pick by how deep you want to go.
Bluetooth code reader (~$25)
Veepeak OBDCheck BLE →
Pairs with your phone — reads and clears codes, live data.
Serious DIY (~$100)
BlueDriver Pro →
Enhanced codes (ABS, airbag, TPMS) plus repair reports.
Shop-grade tablet (~$300+)
Autel MaxiCOM MK808S →
Bidirectional tests, service resets, all systems.
As an Amazon Associate, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.
Other Powertrain codes on this vehicle
00532
Supply Voltage B+ Signal too Low
16394
Camshaft/Crankshaft Position Correlation Bank 1
16395
Camshaft Position Actuator Circuit/Open Bank 1
16486
Mass or Volume Air Flow Circuit Low Input
16487
Mass or Volume Air Flow Circuit High Input
16500
Engine Coolant Temperature Circuit Malfunction
16501
Engine Coolant Temperature Circuit Low Input
16502
Engine Coolant Temperature Circuit High Input
16514
O2 Sensor Circuit Bank 1 Sensor 1
16515
O2 Sensor Circuit Low Voltage Bank 1 Sensor 1