Advanced Automotive Fault Diagnosis
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LÔØI NOÙI ÑAÀU, ledklok
- Điều hướng trang này:
- 2.6 Fault codes 2.6.1 Fast and slow
| 2.5.12 Back probing connectors
Just a quick warning! If you are testing for a sup- ply (for example) at an ECU, then use the probes of your digital meter with care. Connect to the back of the terminals; this will not damage the connecting surfaces as long as you do not apply excessive force. Sometimes a pin clamped in the test lead’s crocodile/alligator clip is ideal for connecting ‘through’ the insulation of a wire without having to disconnect it. Figure 2.6 shows the ‘back probing’ technique. 2.6 Fault codes 2.6.1 Fast and slow Most modern vehicle management systems carry out self-diagnostic checks on the sensors and actuators that connect to the vehicle ECU(s). A fault in one of the components or its associated circuit causes a code to be stored in the ECU memory. The codes may be described as ‘fast’ or ‘slow’. Some ECUs produce both types. An LED, dash warning light, scope or even an analogue voltmeter can be used to read slow codes. Normally, slow codes are output as a series of flashes that must then be interpreted by looking up the code in a fault code table. The slow codes are normally initiated by shorting two connections on the diagnostic plug and then switching the ignition on. Refer to detailed data before shorting any pins out! Fast codes can only be read by using a fault code reader or scanner. Future ECUs will use fast codes. In the same way as we accept that a good digital multimeter is an essential piece of test equipment, it is now necessary to consider a fault code reader in the same way. If a code reader is attached to the serial port on the vehicle harness, fast and slow codes can be read out from the vehicle computer. These are either displayed in the form of a two, three or four digit output code or in text format if soft- ware is used. tải về 7.07 Mb. Chia sẻ với bạn bè của bạn:
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