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ELM329P 参数 Datasheet PDF下载

ELM329P图片预览
型号: ELM329P
PDF下载: 下载PDF文件 查看货源
内容描述: CAN解释 [CAN Interpreter]
分类和应用:
文件页数/大小: 76 页 / 353 K
品牌: ELM [ ELM ELECTRONICS ]
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ELM329  
Interpreting Trouble Codes  
Likely the most common use that the ELM329 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:  
code (0302).  
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 extra bits in the  
first digit as follows:  
If the first hex digit received is this,  
Replace it with these two characters  
>01 01  
To which a typical response might be:  
41 01 81 07 65 04  
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
P0  
P1  
P2  
P3  
C0  
C1  
C2  
C3  
B0  
B1  
B2  
B3  
U0  
U1  
U2  
U3  
Powertrain Codes - SAE defined  
“ - manufacturer defined  
“ - SAE defined  
The 41 01 signifies a response to the request, and  
the next data byte (81) is the number of current trouble  
codes. Clearly there would not be 81 (hex) or 129  
(decimal) trouble codes present if the vehicle is at all  
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  
Light’) has been turned on by one of this module’s  
codes (if there are more than one), while the other 7  
bits of this byte provide the actual number of stored  
trouble codes. In order to calculate the number of  
stored codes when the MIL is on, simply subtract 128  
(or 80 hex) from the number.  
The above response then indicates that there is  
one stored code, and it was the one that set the Check  
Engine Lamp or MIL on. The remaining bytes in the  
response provide information on the tests that are  
supported by that particular module (see the J1979  
document for further information).  
“ - jointly defined  
Chassis Codes - SAE defined  
“ - manufacturer defined  
“ - manufacturer defined  
“ - reserved for future  
Body Codes - SAE defined  
“ - manufacturer defined  
“ - manufacturer defined  
“ - reserved for future  
Network Codes - SAE defined  
“ - manufacturer defined  
“ - manufacturer defined  
“ - reserved for future  
In this instance, there was only one line to the  
response, but if there were codes stored in other  
modules, they would each provide a line of response.  
To determine which module is reporting, you need to  
turn the ‘headers’ on (with AT H1) which then shows  
the ID bits associated with the message.  
Having determined the number of codes stored,  
the next step is to request the actual trouble codes  
with a mode 03 request (there is no PID needed):  
Taking the example trouble code (0302), the first  
digit (0) would then be replaced with P0, and the 0302  
reported would become P0302 (which is the code for  
an ‘cylinder #2 misfire detected’).  
If there had been no trouble codes in the above  
example, the ECU would have told you so. The  
response would typically look like:  
>03  
43 00  
>03  
That’s about all there is to reading trouble codes.  
With a little practice, you will find it to be quite straight-  
forward.  
A response to this could be:  
43 01 03 02  
The ‘43’ in the above response simply indicates  
that this is a response to a mode 03 request. The next  
byte (the ‘01’) says that 1 trouble code follows, while  
the remaining two bytes provide the actual trouble  
ELM329DSB  
Elm Electronics – Circuits for the Hobbyist  
www.elmelectronics.com  
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