What does it mean?
The troublecode P0103 is set when the MAF sensor signal is consistently high. This code, unlike P0102, is not often encountered. When diagnosing MAF sensor codes, understanding fuel trims is very important. Please see the fuel trims article (P0171): Fuel Trims – Lean Identifying the type of MAF sensor in your car will also aid diagnosis. There are a number of different MAF sensors including the most common hot-wire sensors.
Note: Circuit High Input codes are mostly caused by defective alternators that develop excessive voltages, although there may be other causes as well, such as short circuits that “leak” current into a particular system from other, unrelated systems that work on higher voltages. Note that in the case of short circuits that leak power into a control circuit, there is likely to be other, seemingly unrelated trouble codes present along with the code(s) being investigated.
Diagnosing a “high input” code will always involve a thorough testing of the charging system as a first step, followed by measures to isolate the system from all other possible sources of power during resistance, continuity, and reference voltage tests.