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Choosing a scan tool

A basic code reader shows engine codes and clears the light. A DIY scan tool adds live data and other modules. A bidirectional tool can also command parts and run service functions.

Every OBD2 tool reads
engine and emissions codes, freeze frame, readiness
Needs a better tool
ABS, airbag, body modules, tests and resets

Every car and light truck sold in the US since the 1996 model year has a standard 16-pin diagnostic port and reports engine and emissions faults in the same format. That is why even the cheapest code reader can read a P0 code, show the freeze frame and clear the check engine light.

The differences start beyond the engine computer. ABS, airbag, body and network modules use their own manufacturer data, so a tool has to support your make to read them. Live data, graphing and the ability to save a report make a tool far more useful for actually finding a fault.

A bidirectional scan tool goes one step further: it can switch a fan, a valve or a pump on and off, and run service functions such as an electronic parking brake retract or a battery registration. Coverage varies by make and year, so check the maker's vehicle list before you buy.

Common mistakes

  • Buying a code reader when the light you need to read is ABS or airbag.
  • Assuming a tool covers every function on your car without checking the maker's coverage list.
  • Overlooking update costs: some tools need a paid subscription after the first year or two.

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