How To Make: DIY Airbag Tester for airbag diagnosis.
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This video will show you step by step instructions on how to make a DIY airbag tester so you can test your airbag without the need for an expensive airbag tool.
If you are a professional mechanic, you have customers coming in because the check engine light or the airbag light or any other light is on almost on a daily basis. And if you are like me, your worst nightmare is probably to see some B0028 – RF Airbag resistance low or maybe a B0024 – LF airbag short to ground popping up. When you get a code like this on a car, it’s telling you that the internal circuit of the airbag could be short to ground or open. This is a common problem, especially with older cars.
The first thing that comes to mind is that the airbag itself could need to be replaced if it’s an internal part that is broken. The problem here is that it could also be the clock spring that’s causing the problem. The clock spring is simply a coil that retracts and expands inside its housing as the steering wheel turns. Its function is to maintain electrical continuity for all the components on the driver’s airbag. Since the current goes through the clock spring to the airbag, if the clock spring’s circuit itself is broken, you would get the exact same code as if it was the airbag’s circuit that was broken. The car’s computer can’t really make the difference. And the tricky part here is that you ABSOLUTELY CAN’T measure the resistance inside an airbag to see if the circuit is still good.
Why not you ask?
Because to measure resistance, your multi-meter “sends” a reference current through the positive and measures the resulting current after the resistance. Depending on the car model and multi-meter model, the reference current could be high enough to deploy the airbag, which could be potentially deadly or harmful (trust me, if you never saw an airbag deploy before, you don’t want to be holding it when it happens)!
So the trick here is to make a pretty simple airbag dummy. The airbag dummy is simply 2 wires connected to a fixed resistance imitating the resistance of a good airbag circuit. The idea here is to bypass the potentially broken airbag circuit by connecting a “fake airbag” (the airbag dummy) in good working condition, erase the code, start the car and watch if the code comes back. If it doesn’t, you know that your airbag is faulty and you need to replace it. If it does come back, then the airbag is not in fault and the problem is somewhere else (probably the clock spring) but you’ll have to measure the resistance of the clock spring circuit to check for open or short to ground circuit.
The idea here is to bypass the potentially broken airbag circuit by connecting a “fake airbag” in good working condition, erase the code, start the car and watch if the code comes back.
REMEMBER TO ALWAYS UNPLUG THE BATTERY BEFORE DOING ANY SORT OF TESTING ON THE AIRBAG SYSTEM.
Anyway, I’ll post more detail on how airbag systems work and how to diagnose them in another post so if you need more info make sure to subscribe to the new posts by email or come back in a little while. I will post tons of info regarding that subject.
OK! Now let’s dive in!
TOOLS NEEDED:
- Electrical wire
- 2 needles (or push pins)
- 2-ohm resistor
- Heat shrinking tube – two sizes: 1x the same size
of the wire
1x double of the size of the wire - Wire stripper
- Lighter
- Electrical tape
- Soldering iron
- Multi-meter
- First, cut yourself about 4-6 inches of wire (as needed).
- Strip the two ends of the wire.
- If you use a push-pin, cut it so the two tips of the push-pin are sharp. if you use sewing needles you can just leave them as they are.
- Twist the wire tightly with the needle so we can weld it later.
- (You can test your resistor first to make sure it suits your needs. It should be between 2 and 2.4-2.6 ohms.)
- Install the 2 ohms resistor to the other end exactly as you did with the needle.
- Solder the needle and the resistor to the wire
- Curve the wire just before the resistor and measure the length between the other end of the resistor and the tip of the needle we just weld.
- Cut the wire accordingly and strip the two ends of it.
- Twist one end of the wire with the resistor.
- Install the second needle just like you did with the first one.
- Make sure the length of the wires are correctly sized so the two needles are side by side.
- Solder the resistor and the needle to the wire.
- Put some of the smaller heat shrinking tubes over the soldered portion of the needles and the resistor.
- Apply some heat to the shrinking tube to seal it.
- Quick check-up to verify all the connections are good.
- Insert 2 new shrinking tubes over the needles to keep them separated.
- Apply some heat.
- Cut the bigger shrinking tube about half of the total length from the resistor to the needles and insert it over the two wires leaving only the two needles out.
- Apply some heat again. (Make sure it’s sealing tight.)
- Put electrical tape on it just to make sure it will last longer. Our own model had some cracks in the shrinking tube after a while so to ensure no dirt or water can get in we thought covering it with electrical tape would help a bit.
VOILA!
The 2 needles can now plug in the airbag connector and the 2-ohm resistor will “fake” the airbag. Now, plug the airbag tester dummy in place of the airbag you want to test, erase the code and restart the vehicle. If the code was showing up because of the airbag, it should not show up again. If it does show up again, you know for sure that the problem is elsewhere. It could be the clock spring or an open loop in some other wires. A more thorough inspection could be needed but at least you are replacing a perfectly good airbag for nothing.
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