A modern vehicle can look fine on the outside while its onboard computers have recorded problems you cannot see.
After a collision, electronic systems may store diagnostic trouble codes related to airbags, cameras, radar sensors, steering, braking, parking assistance, and other vehicle functions. Some of those issues may trigger a dashboard warning. Others may only appear when a technician connects a diagnostic scan tool.
That is why a pre repair and post repair scan can be an important part of today’s collision repair process.
A pre-repair scan helps technicians understand the vehicle’s electronic condition before repairs begin. A post-repair scan helps confirm that problems have been addressed and that the repair process has not introduced new faults.
Here is how both scans work and why they can matter after an accident.
What Is a Vehicle Diagnostic Scan?
A diagnostic scan uses specialized equipment to communicate with the electronic control modules in your vehicle.
Modern vehicles can contain dozens of computers controlling or monitoring systems such as:
- Airbags and supplemental restraint systems
- Anti-lock brakes
- Electronic stability control
- Engine and transmission functions
- Adaptive cruise control
- Forward collision warning
- Automatic emergency braking
- Blind spot monitoring
- Lane departure and lane keeping systems
- Parking sensors
- Cameras
- Steering systems
- Lighting
- Climate controls
- Other electronic features
When one of these systems detects a problem, the vehicle may store a diagnostic trouble code, commonly called a DTC.
A scan allows a technician to identify and document those codes.
I-CAR describes a pre-repair scan as part of the damage-analysis or blueprinting process and a post-repair scan as part of final quality control.
What Is a Pre-Repair Scan?
A pre-repair scan, sometimes called a pre-scan or health scan, is performed before collision repairs are completed.
Its purpose is to establish a starting point for the vehicle’s electronic systems.
The scan may reveal diagnostic trouble codes that existed before the repair process begins, including problems connected with the collision and unrelated issues that were already present.
I-CAR notes that a pre-scan can help technicians document active trouble codes and distinguish between pre-existing conditions, collision-related faults, and codes generated later during repairs.
That information can become an important part of the initial repair plan.
Why Is a Pre-Repair Scan Important?
It Can Reveal Problems You Cannot See
Collision damage is not always visible.
A bumper may return close to its original shape after a relatively minor impact while a radar sensor, wiring connection, mounting bracket, or electronic module behind it has been affected.
A warning light is also not required for every electronic fault.
Ford and Lincoln repair guidance, for example, notes that pre-repair scans can reveal diagnostic trouble codes that may not activate a warning light.
Scanning gives technicians another source of information when assessing the vehicle.
It Establishes a Baseline
Knowing which codes were present before repair work begins provides useful documentation.
Suppose the pre-scan shows a fault involving a front radar system after a front-end collision. That information can help technicians investigate the sensor and surrounding components during the repair.
If another code appears later, technicians can compare it with the initial scan.
This gives the repair facility a clearer picture of what changed during the repair process.
It Can Help Build a More Complete Repair Plan
Collision repair often begins with an estimate based on visible damage, followed by a more detailed inspection or teardown.
Network Auto Body describes an estimate as a repair plan based on the information available at the time it is written. Additional information discovered during the repair can change that plan.
Diagnostic scanning contributes additional information early in that process.
If the pre-scan identifies an electronic issue connected with the collision, technicians can research the manufacturer’s procedures and determine what further diagnosis, repair, calibration, or testing may be required.
What Is a Post-Repair Scan?
A post-repair scan is performed after repairs are completed or near the end of the repair process.
It allows technicians to check the vehicle’s electronic systems again and compare the results with the earlier scan.
The goal is to identify remaining faults, confirm appropriate repairs, and detect codes that may have appeared while components were removed, disconnected, replaced, or reinstalled.
General Motors, for example, states that vehicles covered by its procedures should be retested after repairs to verify that identified faults were addressed and that new faults were not introduced during the repair process.
Why Can New Codes Appear During Collision Repair?
Repairing a modern car can require technicians to disconnect or remove many electronic components.
Depending on the damage, work may involve:
- Disconnecting the battery
- Removing bumpers
- Unplugging cameras or radar sensors
- Replacing lamps
- Removing doors or mirrors
- Replacing a windshield
- Disconnecting seat or airbag components
- Performing structural repairs
- Completing wheel alignment
- Replacing electronic modules
Some of these procedures can temporarily generate diagnostic trouble codes.
Others may reveal an actual problem that needs attention.
A post-repair scan helps technicians determine what remains after the vehicle has been reassembled and repaired.
Why Clearing a Code Is Not the Same as Fixing a Problem
A diagnostic trouble code points technicians toward a condition detected by the vehicle. The code itself is not necessarily the underlying problem.
For example, a code could be related to:
- A disconnected component
- Damaged wiring
- A failed sensor
- Incorrect sensor positioning
- Low voltage
- A damaged mounting bracket
- A communication problem between modules
- A component requiring calibration or initialization
Technicians need to determine why the code appeared, follow the appropriate diagnostic procedure, complete any necessary repair, and verify the system afterward.
The post-repair scan helps with that verification process.
Do All Vehicles Need Pre-Repair and Post-Repair Scans?
The requirements vary. Vehicle manufacturers establish their own collision repair procedures, and those requirements may depend on:
- Make
- Model
- Model year
- Vehicle equipment
- Collision location
- Type of repair
- Systems affected
I-CAR advises collision repair professionals to consult OEM repair information because scan requirements can depend on the age of the vehicle, the extent of damage, and the electronic systems installed.
Many manufacturers publish specific scanning requirements.
For example, Toyota states that a diagnostic “Health Check” should be performed before and after collision repairs when the vehicle has sustained collision damage.
Hyundai also requires pre-repair and post-repair scanning under its current collision repair guidance, regardless of whether a warning light is illuminated.
Nissan’s current guidance requires pre- and post-repair diagnostic scanning on 2008 and newer Nissan vehicles.
The correct approach is therefore to research the repair procedures for the specific vehicle rather than assume the same rule applies to every car.
What Is the Difference Between Scanning and ADAS Calibration?
Scanning and calibration are related, but they are different procedures.
A diagnostic scan communicates with the vehicle’s computers and identifies stored diagnostic trouble codes.
ADAS calibration adjusts or verifies the positioning and reference values used by cameras, radar units, and other Advanced Driver Assistance Systems.
A scan may indicate that calibration is needed, but performing the scan does not calibrate the system.
I-CAR specifically distinguishes post-repair scanning from ADAS calibration. Scanning identifies and addresses diagnostic codes, while calibration involves aiming or adjusting applicable sensors according to manufacturer specifications.
Depending on the repairs performed, a vehicle may require:
- A pre-repair scan
- Collision repairs
- Wheel alignment or other mechanical work
- ADAS calibration
- A post-repair scan
- Additional system verification or a road test
The exact sequence depends on OEM procedures.
What Systems Can Be Affected by a Collision?
Electronic systems are positioned throughout modern vehicles.
A front-end impact can affect more than the bumper and grille. A rear impact can involve sensors hidden behind the bumper cover. A side collision may affect doors, mirrors, restraint systems, or blind spot equipment.
Systems potentially affected after an accident can include:
Airbag and Restraint Systems
Modern restraint systems can include airbags, seat belt pretensioners, impact sensors, occupant sensors, and control modules.
A scan may identify stored faults involving these components even when an airbag did not deploy.
Advanced Driver Assistance Systems
Cameras and radar sensors used by ADAS can be positioned behind windshields, bumpers, grilles, mirrors, and body panels.
Collision repairs involving these areas may require scanning, inspection, and possibly calibration.
Anti-Lock Brakes and Stability Control
ABS and electronic stability control rely on sensors and electronic modules that monitor wheel speed, steering input, and vehicle movement.
Damage to suspension, steering, wiring, or related components can affect these systems.
Parking and Surround-View Systems
Parking sensors and cameras can sit directly inside areas commonly affected during low-speed collisions.
A bumper that looks like a simple cosmetic repair may contain multiple electronic components behind the painted surface.
Can a Pre-Scan Find Hidden Collision Damage?
A scan cannot identify every form of hidden damage.
It will not show technicians whether a reinforcement bar is bent, a mounting tab is cracked, or a structural rail has moved unless those conditions cause an electronic system to register a fault.
That is why scanning works alongside physical inspection, teardown, measuring, manufacturer repair procedures, and other diagnostic steps.
Network Auto Body notes that even relatively minor front-end collisions can cause internal damage that is not visible from outside the vehicle.
A thorough damage assessment combines electronic information with a hands-on inspection of the vehicle.
Does a Post-Repair Scan Prove Everything Is Fixed?
A clean post-repair scan is an important quality-control step, but it should not be viewed as the only measure of repair quality.
Some vehicle systems require additional procedures such as:
- ADAS calibration
- Initialization
- Programming
- Wheel alignment
- Functional testing
- Road testing
- Visual inspection
- Measurements
- Manufacturer-specific verification
For example, Network Auto Body’s Jeep collision repair process includes a post-repair diagnostic scan along with ADAS calibration, safety-system verification, and a road test before the vehicle is returned.
The goal is to complete all procedures required for the specific repair.
Why Manufacturer Repair Procedures Matter
Vehicle technology changes quickly, and repair requirements vary between brands and models.
A technician cannot reliably determine every scanning requirement based solely on how severe the accident looks.
OEM repair information may specify:
- When scans are required
- Which scan tool should be used
- Which modules need to be checked
- Whether calibration is required
- Whether components need programming or initialization
- Conditions required before a scan or calibration
- Required post-repair verification
Many vehicle manufacturers publish specific requirements for diagnostic scanning before and after collision repairs.
Following the applicable manufacturer procedures helps technicians determine what the vehicle actually requires.
What Should You Ask Your Collision Repair Shop?
Most drivers do not need to understand every diagnostic code or electronic module in their vehicle.
You can still ask useful questions about how the shop handles electronic diagnostics.
Consider asking:
- Will my vehicle receive a pre-repair scan?
- Does the manufacturer require scanning for this repair?
- Did the initial scan reveal collision-related faults?
- Does my vehicle require ADAS calibration?
- Will a post-repair scan be performed?
- How will the shop verify that affected systems are functioning properly?
- Will completed scans and calibrations be documented?
A collision repair facility like Network Auto Body can explain the procedures required for your particular vehicle.
Pre-Repair and Post-Repair Scans Are an Important Part of Modern Collision Repair
Cars have become increasingly computerized. Collision repair has changed with them.
A dented bumper or damaged fender may sit inches away from cameras, radar sensors, wiring, electronic modules, and safety equipment.
A pre repair and post repair scan gives technicians useful information at two important stages of the repair.
The pre-repair scan establishes the vehicle’s electronic condition and can identify faults that need further investigation. The post-repair scan provides another quality-control check after repairs have been completed.
At Network Auto Body, our collision repair process combines detailed damage assessment, manufacturer repair information, appropriate diagnostic procedures, and final quality-control checks for the specific vehicle being repaired.
Network Auto Body has served Southern California drivers since 1985, with locations in Downtown Los Angeles, North Hollywood, Van Nuys, Valencia, and Oxnard.
If your vehicle has been involved in a collision, contact Network Auto Body to schedule an estimate and learn what diagnostic and repair procedures may be needed to restore your vehicle.
