For the 12v 5 pin electromagnetic (voltage, current, middle) relay, the sensing mechanism is the electromagnetic system. The faults of the electromagnetic system are mainly concentrated in the coil and the moving and static iron cores.
　　
(1) Troubleshooting for 12v 5 pin relay coil
　　
The 12v 5 pin relay coil failure usually results in damage to the coil insulation; mechanical damage causes short circuit between turns or grounding; due to the low power supply voltage, the moving and static iron cores are not closely contacted, so that the current through the coil is too large, and the coil heats up and burns. When repairing, the coil should be rewinded. If the armature does not pull in after the coil is energized, it may be that the connection of the coil lead wire falls off, causing the coil to open. Weld it after checking out the drop-off.
　　
(2) 12v 5 pin relay core failure inspection and repair
　　
The core fault is mainly that the armature cannot be sucked up after the power is turned on. This may be caused by broken coils, foreign objects between the moving and static iron cores, and low power supply voltage. It should be repaired according to the situation.
　　
After power on, the armature is noisy. This may be caused by uneven contact surfaces of the moving and static iron cores, or oil contamination. When repairing, the coil should be removed, and its contact surface should be filed or ground; if there is grease, it should be cleaned.
　　
The high noise may be caused by short circuit or ring breakage, just repair or replace the new short circuit ring.
　　
After the power is off, the 12v 5 pin relay armature cannot be released immediately. This may be caused by the moving iron core being stuck, the iron core air gap is too small, the spring strain, and the iron core contact surface is oily. When overhauling, you should treat it differently according to the cause of the failure, or adjust the air gap to protect it at 0.02～0.05mm, or replace the spring, or clean the oil with gasoline. For thermal relays, the sensing mechanism is a thermal element. The common fault is that the thermal element burns out, or the thermal element malfunctions and does not operate.