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ELM320DSC Datasheet(PDF) 10 Page - ELM Electronics |
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ELM320DSC Datasheet(HTML) 10 Page - ELM Electronics |
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10 / 16 page  Interpreting Trouble Codes 10 of 16 ELM320 ELM320DSC Elm Electronics – Circuits for the Hobbyist < http://www.elmelectronics.com/ > Likely the most common use that the ELM320 will be put to is in obtaining the current Diagnostic Trouble Codes or DTCs. Minimally, this requires that a mode 03 request be made, but first one should determine how many trouble codes are presently stored. This is done with a mode 01 PID 01 request as follows: >01 01 To which a typical response might be: 41 01 81 07 65 04 The 41 01 signifies a response to our request, and the first data byte (81) is the result that we are looking for. Clearly there would not be 81(hex) or 129(decimal) trouble codes if the vehicle is operational. In fact, this byte does double duty, with the most significant bit being used to indicate that the malfunction indicator lamp (MIL, or ‘Check Engine’) has been turned on by one of this module’s codes (if there are more than one), while the other 7 bits provide the actual number of stored codes. To determine the number of stored codes, then, one needs to subtract 128 (or 80 hex) from the number if it is greater than 128, and otherwise simply read the number of stored codes directly. The above response then indicates that there is one stored code, and it was the one that set the MIL or ‘Check Engine’ lamp on. The remaining bytes in the response provide information on the types of tests supported by that particular module (see SAE document J1979 for further information). In this instance, there was only one line to the response, but if there were codes stored in other modules, they each could have provided a line of response. To determine which module is reporting the trouble code, one would have to turn the headers on (ATH1) and then look at the third byte of the three byte header for the address of the module that sent the information. Having determined the number of codes stored, the next step is to request the actual trouble codes with a mode 03 request: >03 A response to this could be: 43 01 33 00 00 00 00 The ‘43’ in the above response simply indicates that this is a response to a mode 03 request. The other 6 bytes in the response have to be read in pairs to show the trouble codes (the above would be interpreted as 0133, 0000, and 0000). Note that there is only one trouble code here. The response has been padded with 00’s as is required by the standard, and the extra 0000’s do not represent actual trouble codes. As was the case when requesting the number of stored codes, the most significant bits of each trouble code also contain additional information. It is easiest to use the following table to interpret the first digit of trouble codes as follows: Powertrain Codes - SAE defined 0 “ “ - manufacturer defined “ “ - SAE defined “ “ - jointly defined 1 2 3 If the first hex digit received is this, Replace it with these two characters Chassis Codes - SAE defined 4 “ “ - reserved for future 5 6 7 Body Codes - SAE defined 8 9 A B Network Codes - SAE defined C D E F P0 P1 P2 P3 C0 C1 C2 C3 B0 B1 B2 B3 U0 U1 U2 U3 “ “ - reserved for future “ “ - manufacturer defined “ “ - manufacturer defined “ “ - manufacturer defined “ “ - manufacturer defined “ “ - manufacturer defined “ “ - manufacturer defined “ “ - reserved for future Taking the example trouble code (0133), the first digit (0) would then be replaced with P0, and the 0133 reported would become P0133 (which is the code for an ‘oxygen sensor circuit slow response’). As for further examples, if the response had been D016, the code would be interpreted as U1016, while 1131 would be P1131. Had there been codes stored by more than one module, or more than three codes stored in the same module, the above response would have consisted of multiple lines. To determine which module is reporting each trouble would then require turning the headers on with an ATH1 command. |
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