Practical Arduino Cool Projects for Open Source Hardware- P39: A schematic or circuit diagram is a diagram that describes the interconnections in an electrical or electronic device. In the projects presented in Practical Arduino, we’ve taken the approach of providing both a photograph and/or line drawing of the completed device along with a schematic. While learning to read schematics takes a modest investment of your time, it will prove useful time and time again as you develop your projects. With that in mind, we present a quick how-to in this section | CHAPTER 15 VEHICLE TELEMETRY PLATFORM 0101 5 C1 Chassis manufacturer-defined 0110 6 C2 Chassis manufacturer-defined 0111 7 C3 Chassis reserved for future use 1000 8 B0 Body SAE-defined 1001 9 B1 Body manufacturer-defined 1010 A B2 Body manufacturer-defined 1011 B B3 Body reserved for future use 1100 C U0 Network SAE-defined 1101 D U1 Network manufacturer-defined 1110 E U2 Network manufacturer-defined 1111 F U3 Network reserved for future use Going right back to the start of this example our DTC value was 0x1771. If we now take the first digit of that code look it up in the Hex column of Table 15-11 and replace it with the matching value in the Prefix column you end up with the final trouble code string P1771. So now we know what the trouble code is a powertrain problem and that this particular code is manufacturer-defined rather than part of the standard. The code alone doesn t really help though so next you need to look it up and find out what problem 771 in a powertrain is keeping in mind that because it s manufacturer-defined the exact same code could mean totally different things depending on what make and model of car you have. Because many manufacturers can be secretive about their trouble codes this can be quite tricky to determine. There are a number of really handy online resources for decoding DTCs including a web site called OBD-Codes at . The OBD-Codes site includes references for different DTCs and forums where people can discuss what different codes mean and what could be causing them. Another handy site is Engine Light Help at which has DTCs and their meanings listed by manufacturer. Assuming our hypothetical car was a Mazda these sites tell us that DTC P1771 indicates TPS circuit open to transmission control module. This could be extremely helpful if you know what a TPS is a Throttle Position Sensor in case you were wondering and why it might be open-circuit or it could be no help at all if you ve never .
