Why does my VW diagnostic codes give "Implausible Signal"?

Question

I asked a question some time ago about a check light, specifically airbag and seatbelt light. I have since then checked the code with a code reader and removed it. Making the car drive without any alarm for 2 months.

I then had a false start and the light came back on, I will go to check the light again. But I wanted to inquire if this is dangerous for the passenger side or if it poorly created that a false start could create an implausible signal, which may make sense but is very poor design?

false start: I refer to turning the key and stopping before the engine has started properly and it then dies by itself before there is any power for the throttle.

Hope to hear some views, the car is VW polo from 2013.

Answer 1

An "implausible signal" is one that doesn't make sense in the context of the system -- for example a signal voltage that is outside of the normal range of a sensor. This could be an early sign of a failing component but in your case it may also be due to the voltage drop that happens normally during a start.

Many electronic components will behave in unpredictable fashion when their supply voltage is low. During a failed start the voltage may go lower than expected. It is also possible that after 14 years the quality grounds or the resistance of connectors in the airbag system have deteriorated and are contributing to out of spec voltages.

Answer 2

I've frequently seen this fault logged by Volkswagens cars that have a poor condition battery, or a battery that has become discharged.

The best probable explanation I can come up with is that the "false start" you described caused a drop or spike in voltage (or even removed voltage from the supply line, depending on what you did with the ignition key) right at the point that the airbag controller was powering up and performing its self-diagnostic.

My advice would be to clear the fault and consider having the battery condition checked by your local garage.