Relay in electrician: how it works, types, connection schemes and fault diagnosis

If your car stopped working headlights, cooling fan or starter clicks, but does not twist – with a probability of 80% to blame relay. This small electromechanical unit is responsible for switching high currents in the control circuits, protecting the buttons, switches and wiring from overheating. For example, starter current Toyota Corolla can reach 200-300 AAnd if it went directly through the ignition lock, the contacts would burn in a month. Relay solves this problem by closing a powerful circuit with a weak signal (usually a slug). 0.2-2 A) from the button.

In this article, we will analyze how the relay is arranged, what are the differences? electromechanical and solid Models, how to check them with a multimeter and why you can not ignore the signs of malfunction. We also provide a connection scheme for popular cars (VAZ 2110, Ford Focus, Renault Logan) and the standard contact compatibility table ISO 7588-2.

1. Relay device: how it works inside

The classic electromechanical relay consists of three key parts:

• 🧲 Coil (winding) Creates a magnetic field when applying voltage. Usually designed for 12 V (in a car) or 24 In (trucks)
• 🔧 Anchor with movable contacts - is attracted to the core of the coil, closing / opening the chain.
• ⚡ Contact group A pair or three contacts (normally open/closed) through which the main current passes.

When applying voltage to the control contacts (85 and 86 standard ISO) the coil generates a magnetic field that attracts the anchor. This, in turn, closes the power chain between the contacts. 30 (general) and 87 (normally open). Some relays have additional contact 87a - normally closed, which opens when triggered.

What the relay looks like inside (photo)

In the photo below - disassembled relay Bosch 0 332 209 150 (applies in VW Golf, Audi A4). The coil (blue), anchor (metal plate) and contact group (silver plates) are visible. The magnetic field of the coil overcomes the force of the anchor spring, closing the contacts.

Critical nuance: relayed protection diode (not in all models) when checking multimeter must take into account the polarity of the connection to the contacts 85/86. The diode only passes current in one direction, and if you confuse the + and the -, the relay will not work.

2. Types of relay: what is used where

In the automotive electrician, two main types of relays are used, differing in principle of operation and reliability:

Type of relay	Principle of work	Advantages	Deficiencies	Application
Electromechanical	The magnetic field of the coil closes the mechanical contacts	Low price, simplicity, repairability	Contacts are worn out, sensitive to vibration	Starters, headlights, fans, fuel pumps
Solid state (semiconductor)	Control via simistor/thyristor without moving parts	Silent work, long service life, no sparkling	Highly sensitive to overheating, radiators required	Audio systems, LED lighting, ignition systems
gercon	Contacts are closed in a glass bulb under the influence of a magnetic field	High reliability, small dimensions	Limited current (up to 2 A), high price	Signals, position sensors

90% of vehicles use standard-sized electromechanical relays (e.g., standard-sized relays). Tyco V23134 or Omron G2R). Solid-state vehicles are less common - they are installed in premium cars (BMW 5 Series, Mercedes E-Class) to manage powerful consumers without noise or vibration.

3. Standard relay contacts

Most of the relays in the car meet the standard ISO 7588-2where the contacts are numbered and have a fixed purpose:

• 🔌 30 General contact (food from the battery or fuse).
• 🔌 87 - normally open contact (closes when triggered).
• 🔌 87a - normally closed contact (opens when triggered). Not all relays.
• 🔌 85 - Control contact (minus or plus, depending on the scheme).
• 🔌 86 Second control contact (opposite polarity to the 85).

Example: in the starter relay VAZ 2107 contact 30 It's connected to the BAC plus. 87 - to the starter, 85/86 - to the ignition lock. When you turn the key to the contacts 85/86 12 V is applied, the coil is triggered and closed. 30 s 87, putting current on the starter.

4. Signs of malfunction of the relay and their causes

The symptoms of a relay breakdown depend on which chain it is installed in. Let's look at the typical cases:

⚠️ Attention: If the starter relay clicks, but the engine does not turn, do not rush to change it. Check it first. body-mass and battery At low voltage (less than 11.5 V), the relay may not keep the contacts closed.

• 🚗 The starter doesn't spin or click: A faulty starter relay or retracting relay. Check the contact. 30 12 V for the presence.
• 💡 The headlamps flash or do not switch on: contact burn 87 in a light relay. Frequently found in Renault Megane and Peugeot 308.
• 🌀 The cooling fan shall not be operated: Check the fan relay (usually located in the unit under the hood). V Opel Astra H This relay often sticks due to corrosion.
• ⚡ The fuses burn out for no reason: Maybe there was a connection in the relay. 30/87.

The main reasons for the failure of the relay:

1. Mechanical wear and tear contact 30/87 They burn with sparkling at high currents.
2. Corrosion - oxidation of contacts due to moisture (relevant for relays in the underhood space).
3. Overloading - if the current passes through the relay above the nominal (for example, with KZ in the circuit).
4. Poor details Cheap relays without a protection diode quickly fail.

5. How to check the relay multimeter: step-by-step instructions

To diagnose the relay, you will need a multimeter in vertebrae or resistance measurement mode. Follow the algorithm:

1. Remove the relay from the pad (crush the locks with a flat screwdriver).

2. Set the multimeter in vertebrae mode (or 200 ohms).

3. Call the coil: touch the contacts with probes 85 and 86. Resistance must be 50-120 Om. If the "1" (cliff) or "0" (KZ) - relay is faulty.

4. Serve 12 V on 85/86 (Consist with polarity if you have a diode). There's got to be a click.

5. Call the contacts. 30 and 87: when applying 12V, the resistance must fall to OmWithout tension, remain infinite.

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If the relay does not click when applying voltage, check:

• 🔋 Polarity of connection to 85/86 (Switch the + and the - places).
• 📏 Integrity of the coil (if resistance "1" is a break of the winding).
• 🔍 Clean contacts (oxidation or dirt can block the response).

To check the relay extractless (for example, in the fuse block) use the "barrier" method:

1. Find the contacts on the diagram. 30 and 87 Relay.
2. Put it in the nests. 85 and 86 lintel (piece of wire). The relay should work.
3. If after that the device (for example, a fan) worked - the problem in the control circuit (wiring, button, ECU).

6. How to replace the relay in the car: step-by-step guide

Replacing the relay is a simple procedure, but requires care. You'll need:

• 🔧 A flat screwdriver (to remove the relay from the pad).
• 🔍 Lantern (to see the markings on the case).
• 📋 Scheme of the block of fuses (usually on the block lid or in the manual).

Replacement algorithm:

1. Turn off the power: Remove the "-" terminal from the battery to avoid KZ.
2. Find the faulty relay: Orient yourself according to the scheme on the block cover. For example, in Ford Focus 2 - Fan relay. R12The starter relay. R5.
3. Remove the relay: Carefully tuck it with a screwdriver behind the top and pull it up. Do not make excessive efforts - you can break the pad lockers.
4. Install a new relay: Insert it before clicking, making sure the contacts match. If you have a diode relay, observe polarity (usually marked on the body).
5. Check the work: connect the battery and activate the circuit (for example, turn on the headlights or start the engine).

⚠️ Attention: In some vehicles (e.g., BMW E60) starter relay integrated into control unit DME. Replacing it requires programming – don’t try it yourself!

If the device does not work after replacing the relay, check:

• 🔌 Safety lock in a chain (often it comes in pairs with a relay).
• 📡 Wiring cliffs or corrosion (especially in rations).
• 🔧 Massa on the body – poor contact can block the operation.

7. Popular questions about relay in auto electric

Can I replace the relay with a more powerful one (for example, from 30 A to 40 A)?

Yes, but only if the rated current of the new relay lower original. For example, instead of a relay on 30 A, you can put on 40 A, but not vice versa. Also make sure that the size and the scoring are the same. In the relay with normal-closed contacts (87a) replacement with a normal relay without 87a This will cause the chain to work incorrectly.

Why does the relay click, but the device doesn't turn on?

This points to one of three problems:

1. Contacts burnt. 30/87 Check them with a multimeter in vertebrae mode when triggered.
2. Power circuit break - ring the wire from the contact 87 before the device (e.g., the starter).
3. Insufficient stress on 30 - must be at least 11.5 V. Check the battery and the mass.

How to distinguish a diode relay from a normal one?

Relays with a protection diode have:

• Marking in the form of a diode symbol ( ♥) on the body.
• Polarity of connection to 85/86 (If the connection is not correct, it will not work).
• Higher price (by 20-30% more expensive than analogues without a diode).

To check for diodes, connect the multimeter in vertebrae mode to 85/86 And swap the probes. In one direction the resistance will be ~50-120 Ohms, in the other - "1" (cliff).

Can the relay be repaired or only replaced?

Repairs are only possible for electromechanical relay:

• 🔧 Contact cleanup: Take out the relays, clear the contacts. 30/87 sandpaper (grain content 1000).
• 🧹 Oxidation removal: wipe the contacts with alcohol or a special cleaner (Contact Cleaner).
• 🔨 Replacement of anchor spring: If it weakens, the relay can spontaneously fire.

Solid-state relays are not subject to repair – they are only replaced. It is also not recommended to repair the relay with a sealed body (for example, HELLA 4RA 003 563-031).

Where to buy a relay for a car and how to choose?

When buying a relay, pay attention to:

• 📌 Nominal current (Must be consistent with the original).
• 🔍 Type of contact (normally open/closed)
• 🏷️ Marking (e.g., 12V 30/40A or ISO 7588-2).
• 🔄 Presence of a diode (if it was in the original).

Top producers: Bosch, HELLA, Omron, Tyco. Avoid no-name relays from China – they often have understated current performance.

1. The relay protects the control circuits from high currents by closing them through a weak signal.

2. Standard stitching: 30 - food, 87 - Out, 85/86 - management.

3. Signs of malfunction: clicks without triggering, burnt contacts, overheating of the body.

4. Test: multimeter (coil resistance 50-120 ohms) or by the jumping method.

5. Replacement: select relays with similar parameters (current, type of contacts, polarity).