Audi Common OBD-II Codes: A3, A4, A6, Q5, TT

Audi shares VAG Group platforms and engines with VW, Skoda, and SEAT. A3, A4, A6, and Q5 use EA888 TFSI engines and S-tronic (DSG) transmissions. Understanding their DTC patterns through OBD-II is similar to VW diagnostics but with Audi-specific nuances.

EA888 TFSI 1.8/2.0 (A4 B8/B9, A6 C7, Q5): Known Issues

P2187 — Lean Mixture at Idle (EA888 Gen 1/2)

Same root cause as VW Golf — PCV system in cam cover.

Audi-specific note: On A4 B8 with 1.8 TFSI (CABA/CDAB), the PCV is integrated into the cam cover and fails around 80,000–100,000 km. Oil mist enters intake, ECU sees lean mixture via wideband O2.

Live Data:

• STFT Bank 1 at idle > +8% → lean; confirm with Fuel Rail Pressure at 2,000 RPM: should be 40–80 bar

P0087 — Fuel Rail Pressure: Below Threshold

HPFP (High Pressure Fuel Pump) drive cam follower wear — particularly bad on EA888 Gen 1. Audi part: 06H 109 311.

• Check Fuel Rail Pressure vs Fuel Rail Pressure Setpoint in Live Data
• Difference > 10 bar at steady load → HPFP worn

P0300 / P030X — Misfires (GDI Carbon)

EA888 direct injection causes intake valve carbon buildup. A3/A4 with 2.0 TFSI after 70,000+ km:

• Rough cold idle
• P0300 random misfires (improved when fully warm)

Walnut blast cleaning is the standard fix.

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3.0 TFSI Supercharged V6 (A6 C7, Q7, A8): Codes

The 3.0 TFSI supercharged (CGWB, CJWB) in A6 C7, Q7, and Q5 3.0T.

Common codes:

• P0300 — Carbon buildup misfires (GDI + supercharger = carbon accumulates faster)
• P0171 / P0174 — Lean Bank 1/Bank 2 (PCV failure on supercharged units)
• P2187 — Lean at idle (same PCV issue)

Supercharger-specific:

• P0299 / P2243 — Supercharger boost below threshold → belt or bypass valve fault
• Supercharger Bypass Valve Position at idle should be open (recirculating); at load: closed

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S-tronic DSG: Audi-Specific Codes

Audi uses S-tronic (branded version of DSG):

• DL382 7-speed wet DCT (for higher torque: 2.0 TFSI 190hp+, 3.0 TFSI, TDI)
• DL501 “S-tronic” 7-speed wet (2.0 TFSI/TDI older gen)

Wet DCT (DL382) codes:

• P17BF — Clutch 1: slip
• P175E — S-tronic: oil temperature protection
• P17A0 — Electrohydraulic actuator: pressure fault

S-tronic Live Data:

• DCT Oil Temperature: < 100°C normal; > 120°C → heavy city traffic or spirited driving
• Gear Actual vs Target: should match; delay > 0.5s = solenoid lag

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quattro Driveline Codes

Audi’s quattro system uses several different AWD configurations:

Code	Description
C1234	Torque vectoring: fault (Sport Differential)
C0040	Rear axle speed sensor: signal fault
P0826	Transfer case mode switch: fault
U0402	Lost communication with Transfer Case Control Module

Haldex-based quattro (A3, TT, Q3, Q5 2.0):

• Haldex coupling fluid change every 40,000 km
• P174F — Haldex solenoid: fault

Crown gear quattro (A4, A6, Q5 3.0, Q7): More reliable mechanical AWD, fewer electrical issues

quattro Live Data:

• Rear Axle Torque % vs Front Axle Torque % during acceleration: rear should receive 50–80% during Sport mode

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Audi TDI (2.0 TDI, 3.0 TDI): Diesel Codes

Most A4, A6, Q5 diesels use Bosch Common Rail with DPF+EGR+AdBlue (on 3.0 TDI).

2.0 TDI typical codes:

• P0087 — Rail pressure below threshold
• P2002 — DPF efficiency below threshold
• P0401 — EGR insufficient flow (carbon buildup)
• P0299 — Variable geometry turbo: underboost

3.0 TDI (A6/A7/Q7) typical codes:

• P20EE — SCR NOx catalytic converter efficiency
• P20BA — AdBlue dosing: insufficient flow
• P004A — Turbo B: underboost (twin-turbo system)

3.0 TDI Live Data:

• AdBlue Level < 3L → warning
• NOx Upstream SCR vs NOx Downstream SCR: SCR reduction efficiency > 70% (healthy)

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Audi Virtual Cockpit / MMI: Infotainment Codes

Modern Audi (B9 A4, C7/C8 A6) with Virtual Cockpit:

• U0416 — Data Bus: MMI lost communication
• U0184 — Lost communication with Radio

Often caused by low battery voltage or software corruption.

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VAG Extended Diagnostics: Essential for Audi

Audi requires UDS Mode 22 / VAG Extended protocol for full diagnosis.

With standard OBD-II (Mode 01/03) only:

• Basic P/B/C codes
• ~15 standard PIDs

With VAG Extended (Mode 22):

• All 6-digit proprietary codes (P17xx, U01xx)
• Full ECU parameter sets (200+ PIDs per ECU)
• Adaptation, coding, service reset, S-tronic calibration
• Long Coding / Byte Coding for option customisation

Car Diagnostics supports full VAG Extended protocol for all Audi models.

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Summary Table

Model	Engine	Top Codes
A3 8V / TT 8S	1.8/2.0 TFSI EA888	P2187 lean, P0087 HPFP
A4 B8	1.8 TFSI CABA	P0087, P0300 carbon
A4 B9 / Q5 FY	2.0 TFSI DKZA	P0300, S-tronic P17BF
A6 C7	3.0 TFSI supercharged	P0300 carbon, P0171
A6 C7/C8	3.0 TDI CDUC/CREC	P0087, P20EE AdBlue
Q7/Q5 3.0 TDI	CREC/CRC	twin-turbo P004A

Audi key maintenance: walnut blast GDI engines at 70,000 km, change S-tronic/Haldex fluid every 40,000 km, use correct ACEA C3 specification oil.