Do-it-yourself auto repair

How to check the speed controller

Should the engine of your car stall in the idle run mode, then you probably need to check several detectors (the mass airflow detector, throttle valve position sensor, idle air control valve, NE sensor) in order to define the malfunctioning one. We have viewed earlier the methods of checking the NE sensor, the throttle valve position sensor, the mass airflow detector and the idle air control valve, so now we will observe the checking of speed controller with our own hands.

In case of its malfunctioning this controller may transmit wrong data that may lead to deviations in work of not only the engine, but all the other car units. The car velocimeter (CV) sends signals to the controller, which controls the work of the engine at idle, and also, using the idle air control valve, controls the flow of the air which passed through the throttle body. The bigger is the speed, the higher is the frequency of these signals.

How to check the malfunctioning of the controller:

  • The idle run is not stable;
  • The speedometer is malfunctioning or not functioning at all;
  • Increased fuel consumption;
  • Decreased engine thrust.


The on-board computer may also show the error about the absence of signals on the car speed controller. It is in case when there is an onboard computer installed in the car.

Usually the malfunctioning is caused by the breaking of the chain, so it is necessary first of all to check the integrity of the chain. Firstly you should disconnect the power supply and then examine the contacts whether they are contaminated or oxidized. If there’s some dirt, remove it and put some Litol on the contact. The wires usually undergo the abruption in places near the plug, because it is where they are folded and the insulation may be damaged. You should also check the resistance in the grounding chain, which should be equal to 1 Om. Should the problem be not fixed, then you should check the efficiency of the speed controller. So appears the question: how can we check the speed controller?

how to check the speed controller? 

In the VAZ cars and in some other the installed speed controller usually works according to Hall effect (usually it makes 6 impulses per revolution). But there are some other controllers working on other principles: the controllers with reed switch and flux gate controllers. Firstly we should view the most popular controller, basing on Hall Effect. The controller itself is equipped with 3 contacts: voltage, impulse signal and grounding.

Checking of the speed controller

Firstly we should find out whether there is grounding and 12 V voltage in the contacts. These contacts are checked, and the contact with impulse signals in tested in rotation. The voltage between the output and the mass should be between 0,5-10 V.

Method 1

  1. Disassemble the speed controller;
  2. Use the voltmeter. Find out for what purpose each terminal is used. Then connect the input contact of the voltmeter to the terminal, outputting the impulse signals. The second voltmeter contact is grounded to the engine or body of the car.
  3. Turning the speed controller, find out whether there are signals in the working cycle and then measure the output voltage of the controller. In order to make it you can put the part of the pipe on the controller axe (turn with the speed 3-5 kmH). The faster you rotate the controller, the higher should be the voltage and the frequency on the voltmeter.

Method 2 (without dismantling from the car)

  1. Put the car on the lifting screw in such a way, that one wheel is not touching the ground;
  2. Connect the contacts of the controller with voltmeter;
  3. Turn the wheel and observe, whether there is any voltage.
If there is a voltage and frequency in Hz, then the speed controller works properly.

Method 3 (with the lamp or neon mains screw driver)

  1. Remove the impulse wire from the controller;
  2. Using the neon mains screwdriver find "+" and "–" (having turned on the ignition earlier)
  3. Put the wheel in a position described in the previous method;
  4. Connect the neon screwdriver with the wire “Signal” and manually rotate the wheel. If there’s a “-“ on a screwdriver, then the controller works properly.

If there’s no neon mains screwdriver near, then you can use a wire with the lamp. The checking is performed as follows: connect one side of the wire to the “plus” of accumulator. The other connect to the signal plug. If the controller works, the lamp should blink during the rotation.

Checking of the speed controller Checking with the speed controller tester

The checking of the speed controller gear

  1. Put the car up with the lifting screw in order to hang out any front wheel
  2. Find the gear, using your fingers
  3. Move the wheel with your leg.

the gearing rope of the speed controller 

Feel with your fingers, whether the gear works in a right and stable way. If it’s not then disassemble the gear and find the damaged gear teeth.

The checking of the speed controller with reed switch

The controller sends signals resembling those of orthogonal pulse. The cycle is 40-60% and the switching happens between 0 and 5 V, or from 0 V to accumulator voltage.

The flux gate speed detector checking

The signal which appear due to the turning of the wheels actually resembles the oscillations of wave impulse. That’s why the voltage changes according to the revolution rate. The process is the same as with the NE sensor.

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