🚗 Understanding CDD File in UDS Diagnostics.
In automotive diagnostics projects, one file that every validation engineer works with almost daily is:
👉 CDD File
Whether it is:
✔ UDS Testing
✔ CANoe Diagnostics
✔ ECU Validation
✔ Flashing Activities
✔ DTC Verification
✔ Automation Testing
CDD becomes one of the most important files during the entire validation cycle.
But in many projects, engineers use CDD files daily without clearly understanding:
• What exactly CDD contains
• How CANoe uses it internally
• Why diagnostics fail when wrong CDD is loaded
• How sessions, DIDs, NRCs, and security access are linked with CDD
• Why diagnostics debugging becomes difficult without proper CDD understanding
And in real projects, many diagnostics issues are not actually ECU software problems.
Most of the time, root cause comes from:
❌ Wrong DID configuration
❌ Session mismatch
❌ NRC mapping issue
❌ Incorrect scaling
❌ Wrong security configuration
❌ Old CDD version
That is why understanding CDD deeply is very important for every diagnostics engineer.
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# 🔹 What Exactly is a CDD File?
CDD stands for:
👉 CANdela Diagnostic Description
It is a diagnostics database file used mainly in Vector tools like:
✔ CANoe
✔ CANalyzer
✔ CANdelaStudio
A CDD file defines complete UDS diagnostics behavior of an ECU.
In simple words:
👉 CDD acts like a diagnostics dictionary between ECU and CANoe.
Without CDD:
CANoe only sees raw hexadecimal diagnostic communication.
With CDD:
CANoe understands:
✅ DID Names
✅ Diagnostic Sessions
✅ NRCs
✅ Security Access
✅ Routine Definitions
✅ DTC Information
✅ Physical Parameters
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# 🔹 Why CDD is Important in Diagnostics Testing?
During diagnostics testing, ECU communication happens completely in hexadecimal format.
Example:
Request:
22 F1 90
Response:
62 F1 90 54 45 53 54 56 49 4E
Without CDD:
Tester only sees hexadecimal bytes.
With proper CDD:
CANoe directly displays:
✅ VIN Number
Now imagine diagnostics validation with:
• Hundreds of DIDs
• Multiple ECUs
• Multiple software variants
• Different sessions
• Security-protected services
Without CDD:
Diagnostics testing becomes almost impossible.
That is why every diagnostics tester heavily depends on proper CDD configuration.
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# 🔹 What Information Exists Inside a CDD File?
CDD does not only contain DID names.
It contains complete diagnostics behavior of an ECU.
Mainly it contains:
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## ✅ 1. Diagnostic Services
CDD defines all UDS services supported by ECU.
Examples:
• 0x10 → Diagnostic Session Control
• 0x11 → ECU Reset
• 0x22 → ReadDataByIdentifier
• 0x2E → WriteDataByIdentifier
• 0x27 → Security Access
• 0x31 → Routine Control
• 0x19 → ReadDTCInformation
These services are used daily during diagnostics validation.
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## ✅ 2. DIDs (Data Identifiers)
DIDs are used to read ECU-related information.
Examples:
• F190 → VIN Number
• F188 → Software Version
• F187 → ECU Part Number
Example:
Request:
22 F1 88
Response:
62 F1 88 31 2E 30 2E 35
With CDD:
CANoe directly displays:
✅ Software Version = 1.0.5
Without CDD:
Tester needs manual decoding.
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## ✅ 3. Diagnostic Sessions
One of the most important areas during diagnostics testing.
Not every service works in Default Session.
Some services require:
✔ Extended Session
✔ Programming Session
Example:
Request:
10 03
Positive Response:
50 03
Now ECU enters Extended Session.
Only after entering correct session:
• Certain DIDs become accessible
• Routines execute properly
• Security access becomes active
Many “Service Not Supported” issues during testing are actually caused by:
👉 Wrong diagnostic session.
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## ✅ 4. Security Access
Certain services are protected because OEMs do not want unauthorized access.
Examples:
• Flashing
• Variant Coding
• Calibration Updates
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Typical flow:
Seed Request:
27 01
Seed Response:
67 01 12 34
Then tester sends calculated key:
27 02 XX XX
If security configuration inside CDD is wrong:
❌ Security unlock fails.
This is one of the most common diagnostics integration issues.
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## ✅ 5. NRC (Negative Response Codes)
During diagnostics testing, ECU may reject requests.
Example:
Request:
22 F1 AA
Response:
7F 22 31
Meaning:
7F → Negative Response
22 → Requested Service
31 → Request Out Of Range
CDD helps CANoe properly decode NRC information.
Without proper NRC mapping:
Debugging becomes difficult.
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## ✅ 6. Routine Control
RoutineControl (0x31) is heavily used during:
✔ Flashing
✔ ECU Self-Test
✔ Memory Erase
✔ Calibration Activities
Example:
Request:
31 01 FF 00
Positive Response:
71 01 FF 00
CDD defines:
• Routine IDs
• Input Parameters
• Output Parameters
• Session dependency
• Security dependency
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## ✅ 7. DTC Information
CDD also contains:
✔ DTC Definitions
✔ Fault Descriptions
✔ Failure Conditions
Example:
ECU reports:
P0123
CANoe directly displays:
✅ Throttle Position Sensor High Input
instead of raw hexadecimal data.
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## ✅ 8. Scaling and Units
Some DIDs contain raw numerical values.
CDD defines:
✔ Factor
✔ Offset
✔ Units
Example:
Battery Voltage Raw Value:
120
Factor:
0.1
Actual Voltage:
12V
Without scaling:
Raw data becomes meaningless.
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# 🔹 How CDD Helps During CANoe Diagnostics Testing?
During diagnostics validation, CDD helps CANoe:
✔ Automatically decode responses
✔ Display readable DID names
✔ Interpret NRCs
✔ Handle sessions
✔ Execute routines
✔ Support diagnostics automation
✔ Generate diagnostics panels
Without CDD:
Most diagnostics activities become manual and time-consuming.
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# 🔹 One Common Real-Time Issue — Wrong CDD Version
This is probably one of the biggest issues during diagnostics integration.
Software team updates:
• DID definitions
• Security configuration
• Session requirements
• NRC behavior
But validation team accidentally uses old CDD.
Now CANoe starts showing:
❌ Wrong DID decoding
❌ Missing services
❌ Incorrect parameters
❌ Security failures
❌ Automation script failures
Eventually root cause becomes:
👉 Wrong CDD Version
This happens very frequently during vehicle integration phases.
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# 🔹 Difference Between DBC and CDD
Many beginners confuse DBC and CDD.
## ✅ DBC
Used for:
✔ CAN signal decoding
Contains:
• CAN IDs
• Signals
• Scaling
• Byte Order
## ✅ CDD
Used for:
✔ UDS diagnostics decoding
Contains:
• Diagnostic Services
• DIDs
• Sessions
• Security Access
• NRCs
• DTC Information
Both are important…
but both solve different problems.
