History

OBDII is a great tool to give technicians access to many vehicle parameters which are interesting and sometimes even useful for diagnostic purposes. Applications range from free to $$ and vary in features and the number and type of parameters they can read. A little while ago I purchased a ELM327 WiFi OBDII module from eBay. The module looked exactly the same as another one I had seen in use but mine didn't work.

WiFi OBDII module (ELM327)

Problem

The WiFi access point "WiFi_OBDII" would appear and sometimes I could connect to WiFi but then failed at various points when the actual OBD software was trying to connect. Once it had been plugged in for a few minutes the WiFi connection could no longer be found. 

WiFi_OBDII connection error

The eBay seller sent me another unit but it exhibited the same symptoms so he refunded my purchase cost and let me keep the two modules. I purchased another module, from another eBay supplier and it worked fine. Now that I had two faulty modules I set my mind on fixing the faulty modules.

Solution

A simple optical comparison between the two modules showed the non-working modules were missing a solder bridge on the WiFi submodule pin header:

Faulty module
Working Module

The fix is easy: solder a bridge between the two pins on the faulty module.

Summary

The modules are now working but I suspect there is another problem still to be resolved.

The voltage regulators on the main board can only deliver a low current (~100mA) according to the data sheet. The WiFi submodule data sheet mentions operating current of up to 200mA.
I suspect the design of this board requires good quality regulators which can tolerate an overload situation. There is no visible difference in these components between working and non-working boards but I guess the non-working boards have a very cheap regulator (fake brand) which can cause the output voltage to collapse at sporadic intervals and temporarily interrupt the WiFi connection.

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