Starter Solenoid: The Definitive Guide
It’s quite ashamed to admit that we actually know nothing about our core product – starter solenoid. Although we are a leading Chinese Starter Solenoid Manufacturer, that has been specializing in developing & manufacturing starter solenoid for 12 years.
Recently I asked our engineers a few questions about the starter solenoid:
“Do you know how to replace a starter solenoid?”
“Do you know how to repair a broken starter solenoid?”
“Well, I know how to assemble a starter solenoid.”
“Do you know how to start your car with a broken starter solenoid?”
“I guess you’d better call for help?”
“Do you know……”
So yes, we nearly know nothing about the starter solenoid that most people want to know. But not anymore! We made this guide for you, to help you know more about starter solenoid.
From what is it, to how to wire it, from how to replace it to how to repair it by yourself.
Trust me, this is the best starter solenoid guide online.
Chapter 1: What is a starter solenoid
What is a Starter Solenoid
A starter solenoid is a combination of solenoid and switches (Full name: Starter Solenoid Switch). It is one of the main components of the car starter (Motor, Starter Bendix Drive, Starter Solenoid)
As we all know, the starting of the engine requires external support, and the car starter is playing this role. In general, the starter uses three components to achieve the entire starting process.
- The motor receives electric current from the battery and make the starter drive gear generate mechanical movement;
- The Bendix drive engages the pinion gear into the engine flywheel and disengages automatically after the engine start.
- And the starter’s on/off function is controlled by the starter solenoid.
Starter Solenoid Functions
Starter Solenoid has two functions:
1. To control the start circuit on / off (Connect the battery to the starter)
2. Drive the starter pinion engaging in the flywheel ring gear.
The electromagnetic force of the solenoid switch sucks the movable iron core in the Starter Solenoid to contact the two terminals, one of which connect to the positive pole of the battery and the other terminal to the starter.
The electric current divides into two streams flowing through the Starter Solenoid:
A ). A stream flow through the sucking coil, generating a magnetic force to sucks the movable iron core and move the fork backward so that the starter pinion can engage the engine flywheel.
B). The another stream flows through the holding coil, creating a magnetic force to keep the core in the post-pulling position until the starting complete.
Where is the starter solenoid
In a car starter motor with Starter Solenoid, the Starter Solenoid is usually mounted directly on the to of starter motor. So where is the starter motor, where is the starter solenoid.
Starter Solenoid Operation
The whole process of starter solenoid switch can be divided into 3 stages: Sucking, holding, return.
When the ignition switch turns to the START position, the battery current flows to the sucking coil and hold coil.
The current then flows from the sucking coil to the armature coil thus make the coil rotated at a low speed.
In this way, the movable core of the solenoid switch sucks into the core.
Through the sucking operation, the starter drive pinion will be pushed out and engaged with the ring gear. Also, the contact plate closes the main contact point.
When the main contact point of the plate close, no current flows through the sucking coil. So, the magnetic field coil and the armature coil can get the electric current directly from the battery.
The armature coil then begins to rotate at high speed, and the engine starts.
Because no current flows through the sucking coil, so the moving iron core can only hold the coil in a fixed position by the magnetic force.
When the ignition switch turns from START to ON, the current flows from the primary contact side to the holding coil via the sucking coil.
In this point, since the magnetic force formed by the sucking coil and the holding coil neutralize each other, they lose the force to hold the movable core.
Thus, the plunger is pulled back by the return spring force, and the contact plate is disconnected, the starter stops.
Chapter 2: Starter Solenoid Troubleshooting
Starter Solenoid Problems
The starter solenoid has four common problems:
1) The suction fails occasionally, or works in engine cooling only and fails in engine warming up.
2) When starting up, the starter solenoid can not reset. Release the start button, the starter remains in operation and only stops when power off.
3) The elastic force of the return spring weakens after repeated use, resulting in that the drive gear of one-way clutch cannot be restored timely, but driven and reversely dragged by the flywheel ring gear.
4) When the starter starts, it will make a periodic noise from the starter solenoid, but the starter does not rotate.
Symptoms of a bad starter solenoid
A multimeter is needed to test and verify the problems of the starter solenoid, but before the testing, the following table can be used to determine whether the starter solenoid works:
|Fault symptom||Possible reasons for the failure|
|The starter solenoid make the clicking noise continuously||The starter solenoid holding coil keep holding or the contacts sealing-off|
|After switching on the starter, the starter solenoid makes the clicking noise, slightly moves but does not rotate.||a.The connection between the solenoid and starter is defective
b.Starter solenoid is broken
|The start button has disengaged, and the drive gear has returned, but the starter continues to rotate.||The starter solenoid contact burn-out|
|The start button is disengaged, the starter continues to rotate, but the drive gear can not reverse.||The starter solenoid has contact burnt, or the movable iron core and return spring cannot move due to no enough elastic force(poor quality)|
Test a starter solenoid with a multimeter
Set the multimeter dial to continuity mode, connect the multimeter probes to the solenoid terminal post( the one used to connect to the motor body) and the solenoid shell.
If there is a resistance, then the holding coil is good.
If the resistance is zero, then the circuit might be shorted.
If the resistance is infinite, then the circuit could be broken. If there is a short circuit or broken circuit, you should replace the starter solenoid.
If your multimeter has the continuity mode, it will be even easier to figure out your starter solenoid condition by testing the continuity of each connection.
Set the continuity mode, check the continuity between Terminal S and M. If there is a continuity,(The screen displays a value of zero (or near zero), and the multimeter beeps. ) replace the solenoid.
Set the continuity mode, check the continuity between Terminal S and the machine body. If there is no continuity(The screen will display 1 or OL (open loop).), replace the solenoid.
Set the continuity mode, check the continuity between Terminal M and B. If there is continuity(The screen displays a value of zero (or near zero), and the multimeter beeps. ), replace the solenoid.
Starter Solenoid No-load Test
1.Starter Solenoid Sucking Coil Test
Disengage the outer lead of the starter field winding (Terminal C, see Fig. below), connect the positive pole of the car battery to Terminal 50, and negative pole to the starter Terminal C and the shell.
At this point, the drive gear should move forward.
If not, the solenoid sucking coil is very likely damaged.
2. Starter Solenoid Holding Coil Test
If the drive gear in the previous test can move forward, then disconnect the Terminal C and connect it to the wire of the battery terminal negative, as shown in Figure, the drive gear should remain outside.
If the drive gear reverses, it indicates that the solenoid holding coil is damaged.
3. Starter Solenoid Spring Test
Based on the above test, disengage the shell wire connected to the battery terminal negative, as shown in Figure below.
Normally, when the battery terminal negative is disengaged, the drive gear should reverse rapidly.
If the drive gear cannot reverse, it indicates that the solenoid return spring is damaged.
Troubleshooting/test a starter solenoid with a screwdriver
A screwdriver can also be used to test the starter solenoid if you don’t have a multimeter.
And it also is a quick and easy method to diagnose the solenoid starter solenoid clicking noise problems.
Connect the two terminal posts of the starter solenoid with a screwdriver, if the starter does not rotate, the malfunction lies in the starter. If the starter functions well, the malfunction lies in the solenoid switch and is often caused by the ablation of the starter solenoid contacts.
Also, you can try to shake the connecting line of the car battery and the starter, if the starter functions well, then the starting circuit might be in a poor contact. If so, you should check the high temperature or the sparking parts in the starting system circuit.
Bypass Starter Solenoid: Start car with a bad starter solenoid
Sometimes the starter could not rotate, or the rotate speed is low after switch on (brightness of the headlamp is fine), and when the starter stop to rotate, there is strange chugging noise near the starter motor, it indicated that the starter solenoid switch got a problem.
If the solenoid switch got some issues when you are driving, you could use a lead wire to make an emergency starting circuit.
Simply connect the battery terminal anode and terminal B of the starter by a lead wire.
After the circuit is well connected, turn the ignition switch to start position, the starter would work and start the car engine.
Remember to disconnect the wire immediately once the car starts, and find the closest repair shop as soon as possible to fix the starter solenoid problem.
Chapter 3: Starter Solenoid Wiring Diagram
Starting System Wiring Diagram
Firstly, let’s check the of the starting system circuit, the wiring diagram as shown in the Fig. below. There is a connection between the starter, the car battery, and the ignition switch. The working circuit of the starter can be activated after the ignition switch is on.
The starting system wiring diagram is as shown in below image.
While the ignition switch is not turned to the start position, the starter solenoid will not connect to the start circuit, and the starting gear is separated from the flywheel. Once the ignition switch is turned to the start position, the magnetic coil circuit will connect to the circuitry.
The sucking coil circuit is as below:
Car battery anode (+) > fuse > ignition switch (start position) > solenoid terminal 50 > sucking coil > terminal c of the solenoid switch > field coil > positive brush > armature coil > negative brush > ground wire > storage battery cathode(-)
The holding coil circuit is as below:
Storage battery anode > fuse > ignition switch (start position) > solenoid terminal 50 > holding coil >ground wire > car battery cathode (-)
After current passes through the sucking coil and holding coil, as the current direction is identical, the magnetic field is superimposed, the iron core will be sucked in.
Then, the iron core will drive the starter drive clutch to move backward so that the starter gear can mesh with the engine flywheel.
While the starter gear almost completes the meshing (with the flywheel), the iron core will move forward to a particular position, to make the contact panel touch with the contacts. Thus the starter solenoid switch will turn on.
After the starter gear has completely meshed with the flywheel, the iron core will move forward to an extreme position, and the solenoid switch will be pressed tightly and connect to the car starter. In the end, the starter motor rotates, and the engine starts driven by starter drive.
The starter motor circuit is as below:
car battery anode(+) > solenoid switch terminal 30 > contact panel > solenoid switch terminal C > field coil > positive brush > armature coil > negative brush > ground wire > car battery cathode(-)
When the terminal 30 & C of starter motor are connected, the pull-in coil will short out. The position of the iron core after suction can be maintained merely by the magnetic force of the holding coil.
When the ignition switch turns back to On position after cranking the engine, the starting circuit will turn off, and the starter will stop rotating. The starter drive gear returns by the spring, the starter drive gear, will separate with the engine flywheel.
Starter Solenoid Wiring Diagram
Not every car carry the starter relay in starting system, and the starter solenoid wiring diagram can be learned by with or without starter relay type.
1. Starter Solenoid Wiring Diagram – Without Starting Relay Type
The starting system circuit without starter relay set in is shown in Fig. below.
After turn on the ignition switch, terminal 50 of the ignition switch is connected to the B8 node of the central circuit board via the red or black wiring, then to the solenoid terminal 50 of the starter via the C18 node of the central circuit board. The battery anode (+) is connected to terminal 30 of the starter via the black wiring.
When turning the ignition switch to the start position, the current direction is as below:
Car battery anode(+), ignition switch start gear, terminal 50, sucking coil, terminal C, field winding, armature winding, ground wire, car battery cathode(-)
Meanwhile, the current direction that passes through the holding coil is as below:
car battery anode(+), ignition switch start gear, terminal 50, holding coil, bonding, car battery cathode. (The working process has been introduced before in Starting System Wiring Diagram)
2. Starter Solenoid Wiring Diagram – Without Starter Relay Type
To protect the ignition switch, lots of modern cars apply the starter relay to control the starter solenoid. The starter solenoid wiring diagram with starter relay shows in the following Fig.
When the ignition switch has not turned to the start gear, no current will passes through the relay coil, and the starter relay contacts are open. Also, the starter solenoid is not energized, and the drive gear is separated from the flywheel ring gear.
After turning the ignition switch to the start position, the circuit of the starter relay coil will be conductive, and the electric current direction is as below:
After turning the ignition switch to the start position, the circuit of the starter relay coil will be conductive, and the electric current direction is as below: car battery anode > ignition switch terminal 1 > ignition switch terminal 3 > starter relay terminal (The one use to connect to ignition switch) > coil ground wire > car battery cathode.
After the starter solenoid coil is conductive, the starter relay contacts will be closed, and connect to the sucking coil and holding coil circuit. (The working process has been introduced before in Starting System Wiring Diagram)
In the starting system with an electronic-controlled engine, the ground terminal of the starter relay coil is connected to the neutral position of the ignition switch (cars with automatic transmission can only start the engine in the position P & N ) or the interlock switch of the clutch, as shown in the left Fig.
Starter Solenoid Wiring
How to wire a starter
Most of the solenoids are installed directly on the starter, and they are closely related to each other. Hence, before learning how to wire a starter solenoid, the starter’s wiring should be studied.
A four-terminal starter has two thick terminals and two thin ones, it might be a little confused to find out which is which if you are not a professional.
The 2 thick terminals post
One of the 2 thick terminals posts is connected to the car battery, and the other is connected to the field winding inside the starter via the conducting plate on the shell of the starter.
Therefore, the thick terminal post with conducting plate shall be connected to the field winding, while thick terminal post without conducting plate shall be connected to the car battery.
But if the conducting plate is not there, how to distinguish between the 2 thick terminals, then?
Actually, the sucking coil inside the starter solenoid switch is connected to one of the thick terminals via the welding spot, then to the field winding, the armature winding and finally to the negative brush bonding. Therefore, the thick terminal with one thread end should be connected to the field winding, while thick terminal without thread end should be connected to the car battery.
The 2 thin terminals post
The terminal post with 2 thread ends (the sucking coil and holding coil are welded together via the welding spot and then connected to the thin terminal) is pull-in terminal, (namely, the solenoid terminal)
The other thin terminal post is directly connected to the shrapnel inside the motor, so thin terminal without thread end is the ignition switch terminal.
How to wire a starter solenoid
There are 3 terminals on the solenoid insulating cover (also called starter solenoid cap), those are, terminal B (or 30), terminal M (or C) and start terminal S (or 50).
Sometimes, there are 4 terminals on the solenoid cap, and those are: terminal B (or 30), terminal M (or C), start terminal S (or 50) and ignition terminal R (or 15a), as shown in Fig below.
Terminal B and Terminal M are usually copper bolts with a thickness of 8mm or 10mm, the one with lug plate is terminal M, which is the power supply terminal of the motor field winding; the other one is terminal 8, which is the power line terminal of the car battery.
Start terminal S and ignition terminal R are usually iron bolts with a thickness of 4mm or 5mm, the one with lug plate is starting terminal S, the electric wire of which is led to the starter relay; the other one is ignition terminal R, the electric wire of which is led to the additional resistance of the ignition coil. The solenoid shell is also an invisible terminal 31(the ground wire).
The switch part of starter solenoid is composed of a main contact plate and contacts. The main contact plate is fixed to the front end of the movable iron core push rod, and the two contacts are respectively integrated with the double-screw bolt of the connecting lead terminal C and the power supply terminal 30.
Near the switch contacts, there is an additional resistance short circuit switch made of a small copper sheet, which is connected to the terminal 15a.
The inner structure of the solenoid is shown in the left Fig.
Chapter 4: How to replace a starter solenoid
Starter Solenoid Replacement
If you want to replace your starter solenoid, you have to take out the starter motor from your vehicle first. The location of the starter motor can be differed by car models, the following instruction is the regular way to replace a starter solenoid. The step 1-7 is about removing a starter motor and step 8-11 about replace a starter solenoid.
Step 1. Disconnect the car battery negative cable
Step 2. Lift the vehicle if the starter motor is under the car.
Step 3. Remove the nut in the starter solenoid terminal.
Step 4. Dismount the terminal of the cable of the car battery anode from the starter.
Step 5. Remove the nut in the starter solenoid terminal S.
Step 6. Remove the retaining bolts in the starter.
Step 7. Take out the starter.
Step 8. Unscrew the retaining nut of the solenoid terminal, as shown in the pictures below.
Step 9. Unscrew the two nuts that fix the solenoid to the shell of the starter Bendix drive and remove the solenoid. As shown in the following picture.
Step 10. Install the new starter solenoid according to the reverse procedure of removing the solenoid.
As shown in the above figure, hook the plunger hook to the starter fork, then use retaining bolts to install the starter solenoid to the starter shell. Note and mark the installation direction of the starter solenoid before the disassembly, if install in the opposite position, the starter will not operate. Connect the motor lead, install and fix with a nut.
Step 11. Starter Solenoid Retesting
After the solenoid is installed, connect the corresponding circuit. The no-load test can be carried out on the car battery to verify the maintenance effect of the starter. The starter can be installed on the vehicle after it operates well in the no-load test. The retest way is as same as the Starter Solenoid No-load Test in Chapter 2.
Step 12. Install the starter motor according to the reverse procedure of removing the starter motor (Step 7-1).
Caution: 5 Tips for replacing a starter solenoid
1. If you lose the retaining bolt of the starter, you should be careful with the length of the new bolt, in case that over-long bolt bursts the coil former (some models of solenoids will not have this fault) and induces ground loop. Also, remember to use a spring washer when installing the bolt.
2. The current of the starter is large in operating and terminal B and terminal M will overheat because of that. So remember to use a spanner to tighten the terminal nuts while you are maintaining your starter solenoid.
3. To avoid the bad contact, the lead wire of the terminal B and terminal M should be clamped with two flat washers.
4. The two retaining bolts in the solenoid cover contacts are quite easy to loose due to the starter vibrating, so they should be tightened whenever maintaining the starter.
5. To reduce the resistance of the movable iron core at work, a thin layer of engine oil should be coated on the surface of the core (anti-freezing engine oil should be used in winter).
Starter Solenoid Price
The starter solenoid prices are differed by different models, quality, and manufacturers. Meanwhile, larger solenoids (such as the Heavy Duty series starter solenoid) tend to be more expensive than smaller ones.
The best is definitely the OEM starter solenoid, and solenoids in the aftermarket are relatively cheaper.
When I was writing this guide, I found a quite interesting book, and there are many electrical accessories’ prices recorded in the book. Part of the starter solenoid prices are as follows:
|Product Name||Model||Reference Price($)||Manufacturer||Power||Rated Current|
|Starter Solenoid||MSO – K50||150.3||Mitsubishi||11kw||80A|
|Starter Solenoid||MSO – K65||231.3||Mitsubishi||15kw|
|Starter Solenoid||MSO – K80||324||Mitsubishi||19kw||135A|
|Starter Solenoid||MSO – K95||368.1||Mitsubishi||22kw||150A|
|Starter Solenoid||MSO – K125||528.3||Mitsubishi||30kw||150A|
|Starter Solenoid||MSO – K150||776.7||Mitsubishi||37kw||200A|
|Starter Solenoid||MSO – K180||810||Mitsubishi||45kw||260A|
|Starter Solenoid||MSO – K220||972||Mitsubishi||55kw||260A|
|Starter Solenoid||MSO – K300||1890||Mitsubishi||75kw||350A|
|Starter Solenoid||MSO – K400||2232||Mitsubishi||110kw||450A|
|Starter Solenoid||MSO – N10||40.05||Mitsubishi||2.2kw||20A|
|Starter Solenoid||MSO – N11||49.14||Mitsubishi||2.7kw||20A|
|Starter Solenoid||MSO – N12||63||Mitsubishi||2.7kw||20A|
|Starter Solenoid||MSO – N18||69.84||Mitsubishi||3.7kw||25A|
|Starter Solenoid||SWO – 0||50||Fuji Electric||2.7kw||20A|
|Starter Solenoid||SWO – 3||46||Fuji Electric||2.2KW||20A|
Chapter 5: How to repair a starter solenoid
Most of the broken starter solenoid switches are repairable, but the labor charge of repairing a solenoid switch tends to be higher than the solenoid switch itself, the repair shops are reluctant to repair the switches, instead of direct replacement is adopted.
We do not recommend non-professionals repair the switches by themselves. The following content is for reference only to those with certain experience. Non-professionals shall seek help from the local mechanic.
Starter Solenoid Disassemble
1.Pull out the movable iron core and spring from the rear end.
2.Seal off the soldering tin at the connection strap of the solenoid box with soldering iron, so that the solenoid coil joint can trip out.
3.Unscrew the two retaining bolts of the switch cap, separate the starter solenoid cap from the solenoid housing, and pull the solenoid axle assembly parts out from the housing(solenoid shell).
Basic Starter Solenoid Repair
1. Starter Solenoid Stuck Issue
The movable iron core should be able to move smoothly. If not, you should find the problem(s) that cause the stuck and fix it. Replace the spring if it’s not in good condition. In most cases, the stuck issue is caused by the bad spring.
2. Starter Solenoid Contacts & Contact Plate burn-out
If the solenoid contacts are not burn-out very severely, then simply use the sandpaper to polish the surface of the solenoid contacts & contact plate.
If the surface is burn-out severity, you should open the solenoid cap, take out the contacts & contact plate, and file the contacts or add the flat washer(s) till two contacts are in same height.(The heights of the two contacts in the switch cap should be consistent)
3. Thread damage of B/M terminal bolts
The terminals usually adopt M8 or M10 copper bolts. The traditional repair method is to dismantle the starter and starter solenoid from the vehicle, disassemble the solenoid, unscrew the terminal bolt, and use the threading die to rethread the terminal bolts.
Starter Solenoid Advanced Test
1.Starter solenoid coil inspection:
Use the R1(Resistance) scale of the multimeter to measure the resistance of the pull-in coil and the holding coil of the solenoid, and the resistance value shall be same with the starter solenoid specification.
If the resistance R=?, the coil is disconnected.
If the resistance is lower than the specified value, the coil has a fault of turn-to-turn short circuit.
(2) Starter Solenoid Working Performance Inspection:
a. Inspection of pull-in and drop-away voltage of solenoid: When inspecting, carry out wiring according to the circuit shown in the right Figure.
Firstly turn on the switch, gradually increase the voltage, when the multimeter (resistance scale) indicates a resistance of zero, the indicated value of voltmeter V is the pull-in voltage of the switch.
Then gradually reduce the voltage indicated value, when the multimeter indicates a resistance of infinite, the indicated value of the voltmeter is the dropout voltage of the switch.
The pull-in voltage shall not exceed 75% of the nominal voltage, and the dropout voltage shall not exceed 40% of the nominal voltage.
b. The ignition coil additional resistance short-circuit switch inspection:
The testing circuit for the short-circuit switch is shown in Fig.2-28. When turning on the switch, the indicator light in the circuit should be brightened up.
c. Starter Solenoid Outage performance Inspection:
When the starter drive gear is stationary and stays in the engaged position, cut off the solenoid power supply. At this time, the main contact of the solenoid shall be able to be interrupted quickly.
Based on the inspections above, solenoids with poor or unqualified performance should be repaired or replaced.
Starter Solenoid Coil Rewinding
(1) Seal off the soldering tin on the connection strap of the switch cap and remove the switch cap.
(2) Clamp the switch housing on the bench screw, unclench the riveting edge of the switch with a screwdriver, and take out the coil assembly.
(3) Dismantle the burned-out coil (if you do not have the specific data, you should record the coil diameters, the number of turns and winding direction of the old coil conductor).
Check the coil frame and the insulating pressing plate; if there is damage, you should repair it according to the original shape.
(4) When rewinding the coil, the diameter, the number of turns and the winding direction of the wire should be identical to the original ones.
In general, the holding coil (thin) is in the inner layer, and the pull-in coil (thick) is in the outer layer, the two coils have the same winding direction, and fish paper should be used to separate the coils and to separate the coil frame and the housing.
(5) The positions of the four outgoing thread end on the two coils shall be distributed as the right figure(a).
Insulation tube shall be sheathed on the ends to prevent the insulation varnish of the wires from wearing out.
(6) Put the felt, coil assembly and iron plate in the switch housing and rivet them properly. Then twist the ends 1 and 2 of the two coils together, and weld starting end 4 of the thin coil on the iron plate (see right image b).
(7) Assembling the contact plate and the switch cap, put out the end 1 and 2 of the coils from the connection strap hole of the solenoid terminal and weld firmly. Pulling out the starting end 3 of the thick coil from the strap hole of the fixed contact plate and weld firmly (see right image c).
In the end, remember to retest the starter solenoid after fixing starter solenoid.(Refer to Chapter 2)
We’re now at the end of The Definitive Guide of Starter Solenoid.
We’ve learned everything from what is a starter solenoid and how to troubleshoot it to repairing a bad starter solenoid switch.
To help tie everything together, we made a checklist to help you remember what we’ve learned from the guide. Also, enable you to quickly find the content that you need.
Here’s is the list:
That’s it, the whole list of The Starter SolenoidGuide.
We hope that reading this guide will help you to know better about starter solenoid.