1. The meaning of fault codes
I think the significance of the existence of fault codes mainly has the following points:
1. Off-line inspection, for the development of parts and components of a vehicle, system integration, and vehicle assembly, the process involved is long and the number of parts is large, which can be said to be quite complicated; in order to ensure that the final vehicle is off-line, and To be able to go on the road safely, it is necessary to ensure that there is no problem with each part itself and between the parts before going on the road, so the fault code detection came into being; not only to ensure that there is no problem with the electronic components themselves, but also to ensure that the electronic components The communication between them is also normal, and ensures the safety of the final vehicle on the road.
2. Fault maintenance, the environment in which the vehicle is located during the entire life cycle of use is also quite complex and harsh; it is a great challenge for the current complex circuit of the vehicle, and at the same time, the troubleshooting of the problem after the problem occurs It is also quite difficult. At this time, we can query the location of the fault through the fault code, and quickly locate and solve it.
2. Classification of fault codes
Our common fault codes are mainly composed of four bytes. The first three bytes indicate the location where the fault code occurs, and the last byte indicates whether there is a fault at this location and what the fault status is.
First of all, let me talk about the description of the 3 bytes that indicate the fault location. When it comes to the fault location, we can’t get around the P, C, B, and U codes that must be mentioned in the fault code; in simple terms, these four The source of the first letter is the four components of the corresponding vehicle, namely Power (power), Chassis (chassis), Body (body), Network and vehicle Integration (U: network and vehicle integration).
Speaking of this, you may be surprised, why the fault code I mentioned is composed of 4 bytes, but in fact the fault codes we see are all Pxxxxxxxxx, Cxxxxxxxx, Bxxxxxxxx, Uxxxxxxxx, which involves message expression and manual identify. In order to facilitate everyone's reading, we have added PCBU codes for classification, allowing maintenance personnel to check and locate problems more quickly. Therefore, there is a corresponding relationship, as shown in the following figure:
byte 0 |
byte 1 |
byte 2 |
byte 3 |
|
|
bit0 - bit7 |
bit0 - bit 7 |
bit0 - bit 7 |
bit0 - bit 7 |
P |
0x00 - 0x3F |
0x00 - 0xFF |
0x00 - 0xFF |
0x00 - 0xFF |
C |
0x40 - 0x7F |
0x00 - 0xFF |
0x00 - 0xFF |
0x00 - 0xFF |
B |
0x80 - 0xBF |
0x00 - 0xFF |
0x00 - 0xFF |
0x00 - 0xFF |
U |
0xC0 - 0xFF |
0x00 - 0xFF |
0x00 - 0xFF |
0x00 - 0xFF |
It can be seen from the above table that the distribution of PCBU codes in byte0 is mainly P (00-3F), C (40-7F), B (80-BF), and U (C0-FF). There is nothing special about byte1 and byte2. Except for industry regulations, they are some fault codes independently defined by each OEM. But for the last byte3, it is the definition of the fault code, whether it is a current fault, a historical fault, or something else. The professional definition is called DTCStatusMask, which indicates the current fault code status.
Our commonly used fault code statuses mainly include bit0, bit3, and bit5, which mainly indicate current faults, historical fault codes, and problem faults after the last clearing.
statusOfDTC (DTC status): bit domain name |
bit number |
bit state |
illustrate |
testFailed (test failed) |
0 |
0 |
DTC did not fail when the request was made |
testFailedThisOperationCycle (test failed in this operation cycle) |
1 |
0 |
DTC has never failed in the current operating cycle |
pendingDTC (pending DTC) |
2 |
0 |
No DTC failures have occurred in the current or previous cycle of operation |
confirmedDTC (confirmed DTC) |
3 |
0 |
DTC was not acknowledged when the request was made |
testNotCompletedSinceLastClear (test not completed since last clear) |
4 |
0 |
Test completed since last DTC cleared |
testFailedSinceLastClear (test failed since last clear) |
5 |
0 |
The DTC test has never failed since the last time the DTC was cleared |
testNotCompletedThisOperationCyce (the test is not completed in this operation cycle) |
6 |
0 |
This operation cycle DTC test is completed |
warningIndicatorRequested (request warning indicator) |
7 |
0 |
Server operation request activates warning light |