Logo carsalmanac.com

How to diagnose the generator brush assembly

Table of contents:

How to diagnose the generator brush assembly
How to diagnose the generator brush assembly

Often in the walls of a car service we hear the same problem - the brush assembly of the generator does not work. Or the generator relay-regulator in the car does not work at all. Let's try to figure out what this problem is and how to deal with it, how to independently diagnose and determine what exactly does not work and what is the cause of the breakdown.

current diagnostics


The first thing that comes to mind with such a problem is, of course, the repair of the generator brush assembly. This is a rather complicated car part, two methods can be used to repair it:

  1. Partial.
  2. Full.

In the case of a partial repair, this refers to a partial disassembly of the generator. This method is worth using if you need to replace one part.

The full way is to remove the generator from the car and completely disassemble it for parts. Try to repair the generator brush assembly in time to prevent bad consequences for the motor of the machines.

Repair Tools

tools for repair
  • Keys for 17 and 19.
  • Headson 19, 17, 10.
  • Collars.
  • Ratchet handles.
  • Extension (with pencil ball).

Remember, the repair and removal of the brush assembly is completely different for each brand of car.


It is worth resorting to replacement if you or your master are sure that the breakdown cannot be fixed by simply replacing the part, then the generator brush assembly must be replaced. To replace the desired part, you must first remove it from the vehicle, for this you will need the specific tools listed above.

What tools will be needed to disassemble the generator itself?

You need:

  • hammer;
  • heads 8 and 10;
  • extended ratchet;
  • ring wrench for 19.

How to check without removing from the car

The so-called correct method. It includes checking the battery circuits. Using a voltmeter, it is worthwhile to carry out the manipulation with the engine running. It is worth recalling that if the engine is not running, the indicator on the voltmeter should be - 12.7 Volts, if another indicator, be sure to recharge your battery. Start the car engine, set the multimeter to 20 volts.

We apply the probes to the terminals, if it shows a voltage of 13 to 14 Volts, this is a normal value. A value of not more than 14.5 Volts is allowed. If, during such a check, your multimeter readings are below 12 or above 14.5, this will indicate a malfunction of the generator relay-regulator in the car. But it is fair to say that not in every caseit is the relay that is broken, often the problem is in the generator itself. The alternator brush assembly can be hidden at the rear of the mechanism. If the relay on your machine is separate from the base itself, pay attention to replacing it, and only if this does not bring results, it is worth starting to replace or repair the generator itself.

alternator brush assembly repair

Checking the combined generator

First of all, we will carry out diagnostics using a combined relay circuit and always with a brush assembly. This type of alternator is very popular today, especially among modern new generation cars. In our case, it is worth removing the part from the machine and disassembling it, since the unit we need is attached at the back, right next to the generator shaft.

  • Find brushes on the generator.
  • Unscrew the fasteners.
  • Remove the brush assembly.
  • Wash off, very often they are all dusted with graphite chips, since the brushes themselves are made of graphite with the addition of special coal.

If you are wondering how to check the brush assembly of the generator, then we use a special circuit to check it, using a power supply with the ability to adjust the load and, of course, a charger. You will also need a 12 volt car lamp and regular wires for system assembly.

Pay attention to your charger, mostly they won't work without a battery.

We connect the wires from the generator relay-regulator to the battery, and also connect a 12-volt light bulb to their brushes. When carrying out such manipulations, try to bebe very careful, as graphite brushes are quite fragile and you can crush them or severely damage them.

If the connection is in the normal state, the light will light up and will burn evenly and calmly, because the brush assembly is the shaft conductor. Remember, in quiet mode, the voltage should be 12.7 volts. Now raise the voltage to 14.7 volts, the lamp should go out. 14.5 volts is the point at which the light bulb burns normally. Try to lower the voltage again, normally the light will light up again, if this happens, then the generator relay-regulator is working properly. If something deviates from the norm, you should think about repairing or replacing the mechanism.

how to check the brush assembly of the generator

Pay attention

Practice has shown that extremely often the main problems with the generator lie in the terminals on the battery themselves. By their nature, they often oxidize, as a result of which voltage passes poorly, making charging difficult, hence the main problems with the generator. Therefore, it is recommended to first rinse the terminals well and only then carry out further diagnostics.

Popular topic