How to Read Audi Engine Codes: Complete Engine Family Identification Guide
You pop the hood, stare at the maze of hoses and metal, and wonder: what engine is actually sitting in your Audi?
Whether you’re ordering parts, diagnosing a problem, or just curious, knowing your engine code is essential. It’s the key to getting the right parts and understanding what’s under the hood. Here’s your complete guide to decoding Audi’s engine identification system.
TLDR: Quick Reference
Audi engine identification comes in two main forms:
- The Badge: A two-digit number (like 40 TFSI or 50 TDI) that tells you the engine’s power output, not its size
- The Engine Code: A 3–4 letter code (like BAM or CTUB) that identifies the specific engine variant for parts and repairs
Where to find them:
- Badge: On the rear of most 2018+ models
- Engine Code: On a sticker in the spare tire well, in the service book, or stamped on the engine block itself
The Badge System: What Those Numbers Actually Mean
If you’ve seen an Audi with “40 TFSI” or “50 TDI” on the back, you’ve seen the badge system. Introduced around 2017, this system replaced engine size labels with power-based classifications .
TFSI vs. TDI: The Basics
| Term | Meaning | Fuel Type | Best For |
|---|---|---|---|
| TFSI | Turbocharged Fuel Stratified Injection | Petrol | Smooth driving, daily commuting |
| TDI | Turbocharged Direct Injection | Diesel | Motorway driving, high mileage, towing |
| TFSI e | Turbocharged Fuel Stratified Injection e-tron | Plug-in Hybrid | Electric + petrol flexibility |
Decoding the Numbers
The two-digit number represents a power band, not engine size. Higher numbers mean more power, regardless of whether it’s petrol, diesel, or hybrid .
| Badge | Power Output (bhp/PS) | Common Applications |
|---|---|---|
| 30 | 110–116 bhp | Entry-level A3, smaller models |
| 35 | 150–163 bhp | Most popular level – A3, A5, Q3 |
| 40 | 190–204 bhp | A5, Q5 mid-range |
| 45 | 245–265 bhp | A5, Q5, A7 higher output |
| 50 | 286–300 bhp | A6, A7, Q7 V6 diesel |
| 55 | 335–370 bhp | High-output models |
| 60 | 429–456 bhp | Performance petrol/diesel |
| 70 | 570+ bhp | Top-tier performance |
“A 35 TFSI Audi produces around 150 bhp. This is Audi’s most popular petrol level… offering an ideal balance between performance and efficiency for everyday driving.”
Important Update: As of 2026, Audi has begun removing these double-digit numbers from the rear of its newest models (like the new A5) for a cleaner look. They still use them in documentation, however .
The Engine Code: The Real Identity
The badge tells you the power level. The engine code tells you exactly which engine you have — and that’s what matters for parts and repairs.
An engine code is a 3–4 letter designation that identifies the specific engine variant . For example, on the B6/B7 generation S4, APY and AMK are 210 bhp versions, while BAM is 225 bhp — all from the same basic engine family .
How the Code System Works
According to Audi experts, the first three characters identify the engine family, while the fourth character identifies the output level .
Example: CTU engine family
- CTUA = 228 kW version (A6/A7)
- CTUB = 245 kW version (S4/S5)
- CTUC = 200 kW version (Q5)
- CTUD = 260 kW version (SQ5)
“You won’t see the fourth letter on the engine itself, as the core engine is the same. Some outlier components and the ECM tuning are what change with the output level.”
Where to Find Your Engine Code
Option 1: The Vehicle Data Sticker (Easiest)
- Located in the spare tire well or on the floor of the luggage compartment
- Also listed in the service book
Option 2: Under the Hood
- On a sticker on the timing belt cover
- Stamped on the engine block itself
Location varies by engine type :
- V6 petrol: Stamped on the right inside of the cylinder block, between the cylinder head and hydraulic pump
- V8 petrol: Stamped on the left side of the cylinder block, above the hydraulic pump
- V6 diesel: Stamped on the right inside of the cylinder block, between the cylinder head and the high-pressure fuel pump
Option 3: The Service Booklet
- The original service book includes the engine code
VIN Decoding: Another Way to Identify Your Engine
Your Audi’s VIN (Vehicle Identification Number) also contains engine information. On the vehicle data sticker, you’ll see a series of codes :
Example: WAU ZZZ 8E Z 3 A 000001
- 8E = Audi A4 Sedan/Estate
- 8H = Convertible
- Additional characters identify the engine type
The VIN is stamped in multiple places:
- On the rear wall of the engine compartment
- On a nameplate under the water collection compartment cover
S, RS, and R8: The Special Cases
High-performance models like S3, RS5, and R8 do not use the number-based badge system . They use S or RS branding to distinguish their top-tier status. For these models, the engine code is even more important for parts identification.
Why This Matters for Owners
1. Ordering Parts
When you need a replacement part, the engine code is essential. A 2.0 TFSI in one year may have different components than the same-size engine in another year. Parts suppliers like AudiParts.niello.com list parts by specific engine codes like CZRA, DSPA, or CNTC .
2. Diagnosing Problems
Engine codes help you research common issues. Knowing your specific variant (e.g., CTUB vs. CTUA) can help you find model-specific forum discussions and repair guides .
3. Performance Upgrades
If you’re considering a remap or upgrade, tuners need to know your exact engine code to deliver the right software .
4. Resale Value
Accurately identifying your engine helps potential buyers understand what they’re getting — and can support your asking price.
Quick Reference: Common Engine Codes
| Engine Code | Engine | Vehicle | Notes |
|---|---|---|---|
| BAM | 1.8T 225 bhp | Audi S3 (8L) | High-output version |
| APY/AMK | 1.8T 210 bhp | Audi S3 (8L) | Lower output |
| CTUB | 3.0T 245 kW | B8 S4/S5 | Supercharged V6 |
| CTUA | 3.0T 228 kW | A6/A7 | Lower output variant |
| CRTC | 3.0 TDI 200 kW | Q7, A4 | EU6 emissions diesel |
Frequently Asked Questions
1. What does TFSI mean on an Audi?
TFSI stands for Turbocharged Fuel Stratified Injection — Audi’s turbo petrol engine technology .
2. What does TDI mean on an Audi?
TDI stands for Turbocharged Direct Injection — Audi’s diesel engine technology .
3. What’s the difference between 30 TFSI and 40 TFSI?
The number indicates power output, not engine size. 30 TFSI is around 110–116 bhp, while 40 TFSI is 190–204 bhp .
4. Does my 2026 Audi still have a number on the back?
Probably not. Audi has started removing the double-digit numbers from the rear of new models for a cleaner look, though they still use them in documentation .
5. Where do I find my Audi’s engine code?
Check the vehicle data sticker in the spare tire well, the service book, or the sticker on the timing belt cover .
6. What’s the difference between engine codes like CTUA and CTUB?
The fourth letter indicates output level within the same engine family. CTUA is 228 kW, CTUB is 245 kW — the core engine is the same, but tuning and some components differ .
7. Do S and RS models use the number badge system?
No, S and RS models use their performance branding instead of the two-digit number system .
Sources & Further Reading:
What Audi are you driving, and what engine code do you have? Share your experience in the comments — it might help another owner decode their ride!
