When a modern vehicle arrives in a bodyshop after a collision, it’s no longer just a case of repairing visible damage. Beneath the surface, there’s a complex network of sensors, modules and electronic systems that need to be checked and verified before the vehicle can safely return to the road. This is where Diagnostic Trouble Codes (DTCs) come into play.
DTCs are the language of a vehicle’s electronic control units (ECUs). They provide a digital trail of what has gone wrong, what systems are affected and how the vehicle’s safety and performance may have been compromised. For bodyshops, understanding these codes is not just about clearing warning lights. It’s about ensuring the vehicle is properly diagnosed, repaired and recalibrated in line with manufacturer standards.
What Are Diagnostic Trouble Codes?
Diagnostic Trouble Codes are alphanumeric codes stored by the vehicle’s onboard computer system whenever a fault is detected. These codes can relate to anything from a disconnected sensor to a misaligned radar system. Each DTC provides vital information that helps technicians pinpoint the source of a fault and determine the appropriate repair procedure.
A typical DTC might look like C1101, P0420, or U0100.
P-codes relate to the powertrain (engine and transmission).
B-codes cover body systems like airbags, doors and seatbelts.
C-codes refer to chassis-related issues such as brakes or suspension.
U-codes indicate network communication errors between modules.
Understanding what these codes mean and how they interconnect is essential when repairing modern vehicles. It’s no longer enough to rely solely on visual inspections or traditional mechanical tests.
Why DTCs Matter After a Collision
A vehicle involved in a collision can store multiple DTCs across various systems, even when there’s no visible damage. For example, a seemingly minor front-end impact can trigger faults in radar sensors, airbag modules or the forward-facing camera used for ADAS functions.
If these codes are ignored or incorrectly cleared, the vehicle may appear repaired on the surface but still carry underlying faults that compromise safety systems. This is particularly important for features like adaptive cruise control, lane-keeping assist and automatic emergency braking. These systems rely on precise calibration, and any undetected fault could result in malfunction during operation.
That’s why pre and post-repair diagnostic scans are now a critical part of professional collision repair. They provide transparency, accuracy and peace of mind for both the workshop and the vehicle owner.
Common DTCs After Collision Repair
While the specific codes will vary depending on the make and model, there are several DTCs that frequently appear following body repairs, ADAS calibration or ECU programming.
1. Airbag and Safety System Codes (B1000–B1999)
Airbag control modules can detect even minor voltage fluctuations or sensor disconnections. Common post-collision codes may include:
B0100 – Airbag module communication fault
B0012 – Driver airbag circuit resistance issue
B0079 – Impact sensor malfunction
These codes often appear when airbags have deployed or when related wiring has been disconnected during repair. Clearing them without a full diagnostic check can lead to system faults or warning light reactivation.
2. Chassis and ABS Codes (C1101–C1299)
Chassis codes are often triggered by issues with wheel speed sensors or braking systems. For example:
C1101 – ABS pump motor fault
C1234 – Wheel speed sensor intermittent signal
C1298 – Yaw rate sensor communication error
After structural or suspension repair, these faults may indicate misalignment, damaged sensors or calibration requirements.
3. ADAS-Related Codes (C1A67, U3000, etc.)
Advanced Driver Assistance Systems are highly sensitive to physical displacement. A millimetre of misalignment can trigger calibration errors. Common codes include:
• C1A67 – Radar sensor misalignment
• U3000 – Control module internal fault
• B1A01 – Camera calibration not completed
If left unresolved, these codes can disable safety functions or cause erratic system behaviour. Accurate recalibration using manufacturer procedures is essential.
4. Communication and Network Codes (U0100–U0299)
Modern vehicles rely on multiple ECUs communicating over data networks such as CAN or LIN bus. After repair, communication faults can occur due to wiring damage, disconnected modules or low battery voltage.
Examples include:
U0100 – Lost communication with ECM/PCM
U0121 – Lost communication with ABS module
U0140 – Lost communication with body control module
These codes often require in-depth network analysis and proper toolsets to identify the root cause.
The Risks of Clearing Codes Without Repair
Some workshops may be tempted to clear codes after repair just to remove dashboard warnings. However, doing so without addressing the underlying issue can result in major safety risks and potential liability.
Clearing a DTC doesn’t fix the fault - it only hides the symptom temporarily. If a vehicle leaves the workshop with unresolved issues, it could cause system failures or insurance complications later on.
Professional diagnostics ensure that every stored code is properly investigated and resolved. It also provides traceability, as pre - and post-scan reports serve as documented proof of the repair quality.
How Collision Assist Supports Bodyshops
At Collision Assist, we work closely with bodyshops to provide advanced vehicle diagnostics, ECU programming and ADAS calibration services. Our technicians use manufacturer-approved equipment to perform accurate scans and pinpoint faults across all systems.
We handle everything from pre-repair assessments to post-repair verification, ensuring each vehicle meets OE standards before delivery. Whether it’s recalibrating radar systems, resetting airbag modules or identifying intermittent communication errors, our process eliminates guesswork and saves valuable workshop time.
Our reports give bodyshops confidence in the repair process, supporting insurance claims and customer assurance. We also assist with remote programming and software updates, ensuring vehicles are restored to full manufacturer specification.
The Future of Diagnostics in Collision Repair
As vehicle technology evolves, the complexity of DTCs will only increase. Electric vehicles, for example, introduce new layers of data related to high-voltage systems, battery management and regenerative braking. Similarly, the growing reliance on sensor networks means more opportunities for fault codes to appear after even minor repairs.
Bodyshops that invest in proper diagnostic partnerships are the ones who will stay ahead. With the right tools, training and support, they can deliver higher repair accuracy, fewer comebacks and safer vehicles for customers.
Get in Touch
Understanding Diagnostic Trouble Codes is no longer optional - it’s fundamental to modern collision repair. Each code tells part of the vehicle’s story, revealing what systems were affected and how to restore them safely.
By working with specialists who understand the technology, like Collision Assist, bodyshops can enhance repair quality, maintain compliance with manufacturer standards and build long-term trust with their customers.
If you want to learn more or discuss how we can support your workshop or vehicle, please contact us here, email enquiries@collisionassistltd.co.uk or call 01427 820808.
Have more questions about our diagnostic process or what to expect from our services? Our FAQ page provides clear answers to the most common inquiries from our partners.
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