On my 2004 TF 135, before I got a pscan, I had mixed success with cheap ELM 327 OBD2 readers from eBay costing around a fiver.  I have one that works with the TF and one that doesn't.  The latter isn't faulty though because it works fine with my MB VIto. 

These readers communicate with the phone, via bluetooth, running an app called Torque.  Bluetooth is the problem here for iPhone users.  My understanding is that Apple, in their wisdom, chose not to implement bluetooth in the same way as others. 

One solution would be to pick up a cheap second-hand Android phone specifically for use with Torque and your chosen OBD2 reader. You wouldn't need a sim card, just download Torque via WiFi and away you go.

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