In currency, ECU fault judgment has become a maintenance area for many repairmen. If conditions allow, the alternative method is a shortcut to judge faults, but you should take care many points when using this method to test ECU fault.
The basic idea of alternative method is to use a reliable component to replace the inspected components. If it can works after replace, it means the inspected components has faults. If the fault not disappears after replace, then exclude the possibility of inspected components’ fault, and narrow the fault scope. Alternative method applies to many kinds of fault diagnosis. But pertinence is needed when using, because it can save time and improve the successful rate of diagnosis. When testing ECU with alternative method, you should note following points.
- At first, make sure that the ECU, which is used to replace, can work. And confirm that it has the same model and the same program version like the original one.
- Some vehicles’ ECU need to match or program after changed before it can work. Most manufacturers regulate that ECU can be programmed only 3 to 7 times. Otherwise it will cause the failure update of ECU chip information. In a period of time after ECU is replaced, it needs to adjust learning automatically. The relative parameters stored previously will lose. So after replacing the new ECU, if the car still fails to start, don’t judge blindly whether ECU is damaged or not.
3. In special situations, a fault is caused by two or more than two fault points. At that time, if replace only the one of the components, the fault phenomenon may not change, it must replace two or more components (those haven’t been tested) at the same time until the failure phenomenon disappears. And replace the original component one by one, then try to judge the fault position by combining with the accompanying phenomenon.
In our company, there is a WG6101NQE Yangtze River bus which configures with EQ6100N – 30 gas EFI engine. When it ran 50 thousand kilometers, the engine stalled and can’t start again. It was taken back to repair. The repairman doubted that ECU might damage, so he removed a good ECU from the other normal car to test, the car still can’t start. Then the repairman thought that there was no ECU fault. Because he didn’t have spare parts of the ECU and the bus hurried to rush out, the repairman took out the ECU which was replaced just now. Continued to check other parts, he took several day to find out the causes. The ignition coil and ECU damaged at the same time, because there was no idea of ECU fault, he made many detours and wasted manpower and time. This is a typical example which use alternative method to test and cause many detours.
- Alternative method is more effective for the single component which has fault situation. Usually, the method can be mosteffective after diagnose the specific direction and scope by other means. If replace blindly, it may cause secondary damage to the circuit board and components. My company has a WG6122NQM type natural gas bus, which was produced by Wuhan Yangtze River Bus Factory. The engine model is NQ 190 N. When the bus ran 6759 km, the engine stalled suddenly and it can’t start again. The repairman used alternative method to check and found the ECU computer ignition controller was damaged, engine can roll after replaced the ECU, but soon ECU damaged again. ECU computer ignition controller hardly has faults (engine runs 100000 km, the damage rate is not more than 1/1000), and it is not damaged easily. Now, why do those damages appear continuously? Checked the peripheral circuits, the bus circuits adopt the two 12 v battery which produced 24v voltage to supply the electricity for the bus. Ignition circuit and electronic control fuel injection system supplied the electricity by using a power switching regulator which can change 24v voltage to 12 v voltage. Checking the power switching regulator during outputting the voltage, the repairmen found that the voltage was more than 12v and the voltage wasn’t stable. Turned on the power switching regulator, the temperature of a triode was high unusually, and the circuit board had Put-up-iron phenomenon. ECU damage was just the external fault phenomenon. Something wrong with the power switching regulator, it’s the basic cause of the fault.
- for repairing ECU which has integrated circuit multi- pin component,using alternative should more carefully. Usually, carry out the diagnosis only after the clear conclusion is made. Repairmen should have relevant knowledge about the computer, electronic circuits and electronic components. Also, they need excellent welding skills. In general, weld out directly the electronic components which are suspected, and then replace them with the electronic components which have the same model. General electronic components are very cheap in electronic stores. But pay attention to their quality, such as electrolysis capacitor must choose tantalum, silver electrolytic capacitor, and require capacitors with high precision. Meanwhile, during the replacement, welding work must be carried out only when the electricity is cut off.
In general, the control computer of electronic-controlled engine, ECU is rarely damaged. Alternative method just helps to determine ECU damages roughly. Once ECU damages are judged, must determine clearly the causes of damage. According to experience, as for ECU damages, should focus on the stability of the power supply circuits and power supply voltage. Also, pay attention that whether the power supply circuits have poor contact, whether the oxidation and corrosion happen, and so on. If fail to find out the damage causes and just replace the ECU simply after determine the ECU faults, ECU may damage again and again, it may cause unnecessary losses.
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