1. The battery cable cannot be removed before the fault code recorded by the engine electronic control unit is read.
Since the battery cable is detached or the power fuse is detached before the fault code is read, the fault code stored in its random memory is automatically eliminated due to the interruption of the power of the ECU. If you want to obtain the fault information again, you must repeat or reproduce the working condition and environmental conditions at the time of the fault. For an engine that cannot be started, the fault code can no longer be obtained after such operation, and an important fault judgment information is lost. The network expert reminds that before repairing the electronically controlled engine, the fault code recorded by the ECU should be required according to the requirements before other repairs are performed.
2. When the ignition switch is in the on position, the battery cable cannot be removed.
When the ignition switch is in position, never remove the battery cable or unplug the power fuse, regardless of whether the engine is running. Because a sudden power failure will cause the coil in the circuit to generate a self-induced electromotive force, resulting in a high instantaneous voltage, which seriously damages the microelectronic devices such as the ECU and related sensors.
In addition, the wires of other electrical devices with the same battery voltage cannot be removed when the ignition switch is in the ON position. Otherwise, the relevant coil will also generate self-induced electromotive force, thus the ECU or sensor. These electrical devices include: ignition systems, idle stepper motors, programmable read-only memories for ECUs, fuel injectors, air conditioners and other electromagnetic clutches, as well as certain connecting lines for ECUs.
3. Do not use the method of removing the battery cable to clear the fault code.
For most electronically controlled engines, remove the battery cable or remove the fuse to the ECU and keep it powered off for 30 seconds to clear the fault code stored in the ECU. However, for some engines, this method is not suitable, because the memory of the vehicle anti-theft, sound, quartz clock, etc. is also stored in the random access memory. After the power is cut off, the memory will be removed together, resulting in the phenomenon of audio lock code. For these engines, the fault code should be cleared according to the method required in the maintenance manual. Do not remove the battery cable at will.