Bidirectional testing is one of the most powerful features of advanced OBD2 scanners. Instead of just reading data, you can actively control components in your car like lights, door locks, fuel pump, or cooling fan. This allows you to quickly verify if a component is working or if the problem is somewhere else in the system.
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What is bidirectional testing?
Bidirectional testing (also called actuation tests or component tests) allows your diagnostic scanner to send commands to the vehicle and activate specific components.
Instead of only reading data, you can:
- turn components ON/OFF
- simulate real operation
- test systems without using physical switches
Where to find it in scanner
Depending on your tool, it may be called:
- Bidirectional tests
- Actuation tests
- Active tests
- Component tests
Typically located inside:
- Body Control Module (BCM)
- Engine Control Module (ECU)
- Other control modules
Real examples of bidirectional testing
I also have a guide to choosing bi-directional OBD2 scanner – and they make it for smartphones as well so you can even get one for about $100.
Interior lights
You can turn interior lights ON even if the switch doesn’t work.
👉 Useful to confirm if the problem is the switch or wiring.
Door locks
You can lock/unlock doors directly from scanner.
👉 If it works via scanner but not with button → faulty switch.
Engine cooling fan
You can activate:
- Low speed
- High speed
👉 Perfect when diagnosing overheating issues.
Headlights & signals
You can test:
- Low beams
- High beams
- Turn signals
Fuel pump relay
You can activate fuel pump and listen if it runs.
👉 Fast way to confirm pump operation.
Using live data with bidirectional testing
Some scanners allow you to monitor live data while running tests.
Example:
- Command EGR valve open
- Watch percentage opening
👉 If it opens slowly or partially → valve may be clogged.
Why bidirectional testing is powerful
- Saves time during diagnostics
- Helps isolate faults quickly
- Works even when switches fail
- Great for used car inspection
Important note
Available tests depend on:
- vehicle model
- year
- control modules
Even older cars can support basic tests, but newer vehicles offer many more advanced functions.
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Hi, I am Juraj Lukacko. I got frustrated by unhelpful and scammy mechanics, so I decided to learn everything about car diagnostics myself. I test dozens of new car diagnostic tools every month along with learning new strategies to fix and customize cars.
