Maintenance method of automobile relay

- Jan 21, 2021-

Maintenance method of automobile relay

MAD-S-124-C

(1) Simple judgment method of relay performance

Turn on the ignition switch, and then use your ears or stethoscope to listen to whether there is a sound in the control relay, or feel whether the relay is vibrating with your hands. If so, it means that the relay is basically working normally, and the electrical appliances are not working due to other reasons ; Otherwise, it means that the relay works abnormally.


You can also unplug the relay for testing. For example, if the air conditioner compressor does not work, you can start the engine, and then turn on the blower switch and the air conditioner switch. Then unplug the connector of the air conditioner compressor relay to judge. If the sound of the relay can be heard, and the engine speed drops significantly when the relay is unplugged, and the engine speed increases when the relay is inserted, it means that the air conditioner compressor relay and its control circuit are normal.


Regarding the position of the relay, any relay and fuse marked with a dash on the circuit schematic diagram are generally arranged in the central power distribution box.


(2) Common failures of relays: The common failure phenomena of relays include: coil burnout, short circuit between turns (insulation aging), contact ablation, thermal decay, and the inability to adjust the initial operating current.


①The relay coil is burnt out. In order to prevent this from happening, when repairing, maintaining and welding, if the temperature may exceed 80°C, the temperature-sensitive relay and electronic control unit should be removed.


② Contact ablation. For example, the relay of the air conditioner condenser fan of the Jinbei Hiace (parameter | picture) car (using the 491Q-ME engine) is just below the glass cleaning spray pipe. If the spray pipe breaks, the cleaning fluid will leak to the relay. If the normally open contact of the relay is corroded and cannot be disconnected, it will cause the failure of the air conditioner condenser fan to constantly rotate. Therefore, water should be strictly prevented from entering the relay.


(3) Try to reduce the contact resistance of the relay contacts

The contact resistance between the contacts of the automotive relay is mainly composed of the shrink resistance and the surface film resistance. The contact resistance of the contact is related to the contact form, material properties and surface processing of the contact. It can be seen that to reduce the contact resistance of the relay contacts, under the condition of certain contact pressure, you can start by improving the contact state and improving the contact material.


(4) Poor ECU grounding may affect the normal operation of the relay.

A Shenlong Fukang 988 sedan, in normal driving, the engine automatically turned off and restarted, unable to start. Turning on the ignition switch, there is no sound of the fuel pump running, and there is no high-pressure fire. Checking the ignition coil, it is found that there is no power on the plug, but the resistances on the primary and secondary sides are normal.

Measure the spray double-sealed relay of the car, its plug has a 12V power supply. After replacing the jet double-sealed relay, there is still no high-pressure fire or the sound of the relay closing. Use a wire to directly ground the No. 10 pin of the jet dual-sealed relay, and the sound of the relay can be heard, and the engine has started successfully.

But what is strange is that the engine does not turn off when the ground wire is disconnected, and after turning off the ignition switch and restarting the engine, it is normal.

Analyze the reason. This is due to the poor grounding of the engine ECU, which causes the power supply voltage of the relay coil to be very low (sometimes only about 2V), and it is impossible to make the relay pull in. After the wire is directly grounded, the relay has a 12V voltage, so it pulls in smoothly, so the engine starts successfully.

After removing the temporary ground wire (the ignition switch is still on), the relay still has a lower holding voltage (this is a common characteristic of relays). Even if the holding voltage is only 2V, the relay will not break. Turn on, so the engine does not stall. When the ignition switch is turned off, the self-induced electromotive force generated by the circuit is much higher than the power supply voltage. Under the action of this strong electromotive force, the poorly contacted ground may return to normal, so the engine is normal after starting. However, the above faults will reappear, so the way to eradicate it is to thoroughly deal with the poorly grounded parts.