The car either starts or doesn’t start: reasons and what the driver should do

You turn the key in the ignition, but the engine refuses to start. An hour later or the next day everything works like clockwork. Is this a familiar situation? Unstable engine starting is one of the most annoying problems for car owners because it is unpredictable and often has no obvious cause. Unlike a complete failure, when the car does not start at all, periodic failures can indicate a whole range of malfunctions - from a banal battery discharge to serious problems with the electronics or fuel system.

In this article we will look at 10 most common reasons, why the car starts or doesn’t start, and we’ll also give checklists for self-diagnosis. We will pay special attention to those cases when the problem manifests itself only when cold, hot or after downtime. You will learn how to distinguish a starter malfunction from alarm problems, why Diesel engines are more likely to suffer from unstable starting due to high pressure fuel pumps, and when you should immediately go to a service station rather than try to fix the car yourself.

Important: if your car is equipped with a system Start-Stop or a hybrid installation, the reasons may be specific - we will also mention this. And at the end of the article you will find FAQ with answers to the most frequently asked questions and a survey to help us understand exactly what problem you are facing.

1. Battery problems: discharge or poor contact

Let's start with the most obvious - battery. Even if the battery is relatively new, it can cause unstable starting. It's not just about the charge level, but also about the quality of the contacts, the condition of the terminals and even the ambient temperature.

As a rule, if the car does not start in the morning after a night of inactivity or after a long stay, a discharged battery is to blame. But if the problem manifests itself chaotically - today it starts with a half turn, and tomorrow you have to turn the starter for 5 seconds - it’s worth checking:

• 🔋 Charge level (norm: 12.6–12.7 V with the engine off, less than 12.4 V - discharge)
• 🔌 Terminal oxidation (white coating on the contacts increases resistance)
• 🔗 Terminal tightness (check if they are loose)
• 🌡️ Temperature dependence (in cold weather, battery capacity drops by 30–50%)

You can check the battery with a multimeter or a load fork. If the starting voltage drops below 10.5 V, the battery requires replacement. Please note: modern cars with on-board computers and immobilizers may block starting at low voltage, even if the starter is turning.

⚠️ Attention: If after a power surge (lighting up) the car starts, but after a day or two the problem returns, it’s not just the battery that’s to blame. Perhaps generator won't charge or there is a current leak in the on-board network.

2. Starter malfunctions: brushes, solenoid relay, bendix

The starter is the second most common culprit for unstable starting. If when you turn the key you hear:

• 🔊 Clicks without engine rotation → problem in solenoid relay
• 🔄 Slow rotation with extraneous sounds → wear brushes or bearings
• 🛑 Complete silence → open circuit or malfunction ignition switch contact group

Most often they break:

• 🪛 Bendix (overrunning clutch) - does not engage with the flywheel
• 🔌 Brushes - wear out and do not transmit current to the rotor
• 🧲 Solenoid relay — contacts burn out ("nickels")

You can diagnose the starter without removing it: if when you turn the key it turns tightly or jerkily, and after several attempts it “grabs” - most likely the brushes are to blame. If the starter works normally, but the engine does not start, the problem may be flywheel (cut ring teeth) or wiring.

Tap the starter housing with a hammer (sometimes it helps to “revive” the brushes)

Check the voltage at the starter terminals when starting (should be 12 V)

Listen to the sound: a grinding noise indicates problems with the bendix

Evaluate the rotation speed: less than 200 rpm - a sign of malfunction -->

3. Problems with the fuel system: from filter to pump

If the starter turns vigorously, but the engine does not start or stalls immediately after starting, the fault is fuel system. Moreover, the reasons may differ in diesel and gasoline engines.

Typical problems for gasoline engines:

• ⛽ Clogged fuel filter (especially if the car does not start "hot")
• 🚗 Faulty fuel pump (can you hear it buzzing when you turn on the ignition?)
• 🔥 Air leak in the fuel line (check hoses and clamps)
• 💉 Clogged injectors (engine stalls after starting)

Diesels add:

• ❄️ Fuel waxing (in winter, if summer diesel fuel is flooded)
• 🛢️ Fuel injection pump malfunction (high pressure fuel pump)
• 🔥 Problems with glow plugs (engine does not start when cold)

How to check? Listen: if you don’t hear the fuel pump running when you turn on the ignition (in gasoline cars), check its fuse and relay. In diesel engines, pay attention to return - if fuel flows from it, this is a sign of a faulty injection pump.

Symptom	Probable Cause	What to do
The starter turns, but the engine does not start	No fuel supply (pump, filter, broken wire)	Check the pressure in the fuel rail, listen to the pump
The engine starts and immediately stalls	Clogged injectors or air leaks	Carry out diagnostics of injectors, check the tightness of the system
Doesn't start well when cold, ok when hot	Glow plugs (diesel) or temperature sensor (petrol)	Check the spark plugs with a tester, replace the sensor
Doesn't start after refueling	Bad fuel or clogged filter	Drain the fuel, flush the system, replace the filter

⚠️ Attention: If your car is equipped with a system direct injection (for example, FSI or TFSI), faulty injectors can lead to water hammer and engine overhaul. If you suspect problems with injection, immediately contact a service station!

4. Electronics and immobilizer: when the car “does not recognize” the key

Modern cars are literally packed with electronics, and malfunctions in its operation can lead to unstable starting. Most often the culprits are:

• 🔑 Immobilizer - does not recognize the key or chip in it
• 📡 Engine control unit (ECU) — errors in the firmware or oxidation of contacts
• 🔌 Wiring — breaks or short circuits in sensor circuits
• 🚨 Alarm - blocks launch due to failure

How to understand that electronics are to blame?

• Lights up on the dashboard immobilizer icon (a car with a key or a flashing light)
• The engine starts after 2–3 attempts, as if the “resolution” comes with a delay
• After resetting the battery terminals, the car starts normally (but then the problem returns)

What to do? First try reboot the ECUby removing the battery terminal for 10–15 minutes. If this doesn't help, check:

1. Condition chip in the key (try starting with the spare key)
2. Availability errors via a diagnostic scanner (for example, ELM327)
3. Fuses immobilizer and ECU (often burn out during power surges)

How to fool the immobilizer in an emergency?

If the car does not start due to the immobilizer, and you need to drive urgently, you can try the following method (does not work on all cars!):

1. Insert the key into the ignition and turn it to the “ON” position (without starting the engine).

2. Wait 10–15 minutes - sometimes the ECU “recognizes” the key with a delay.

3. Try to start the engine.

⚠️ This method does not guarantee results and can only work if there is a temporary failure. If the problem persists, a diagnosis is required.

5. Sensors: small parts with big impact

The engine of a modern car is controlled by dozens of sensors. If at least one of them produces incorrect data, the ECU may block launch or worsen mixture formation. The most problematic sensors:

• 🌡️ Coolant temperature sensor (DTOZH) - if he is lying, the ECU incorrectly calculates the composition of the fuel mixture
• 💨 Mass air flow sensor (MAF) - if there is a malfunction, the engine may not start “hot”
• 🔄 Crankshaft position sensor (CPS) - without its signal, the ECU will not give the injection command
• 🚗 Camshaft position sensor (CPR) - affects valve timing

How to diagnose? Most sensor malfunctions are recorded in the ECU memory as errors (for example, P0115 — DTOZh malfunction, P0340 - DPRV). You can read them through the diagnostic connector (OBD-II) using a scanner or even a smartphone with an adapter.

If diagnostics are not at hand, try the following method:

1. Start the engine and let it run for 5-10 minutes.
2. Press the gas pedal sharply. If the engine “chokes” or stalls, it’s the fault Mass air flow sensor.
3. If the car does not start after warming up, but starts when cold, check DTOZH.

6. Problems with the ignition system: spark plugs, coils, wires

If fuel arrives, the starter turns, but the engine “does not catch” or runs intermittently, the fault is ignition system. Key points to check:

• ⚡ Spark plugs - wear, carbon deposits or incorrect clearance
• 🔌 Ignition coils - breakdown or breakage of the winding
• 📡 High voltage wires - current leakage or break
• 🔧 Ignition distributor (distributor) - in old cars

How to check?

• Unscrew the spark plug and inspect it: black soot - rich mixture, white - poor, thread oil - problems with piston rings.
• Swap the ignition coils. If the problem “moves” to another cylinder, the coil is faulty.
• Check high-voltage wires in the dark: if visible sparks, there is an insulation breakdown.

Please note: in modern engines with individual coils (one per cylinder) a malfunction of one coil can lead to the fact that the car starts only after 3-4 attempts, and after starting it troits.

7. Mechanical problems: compression, timing, flywheel

If all previous systems are in order, but the car is still unstable to start, the problem may lie in mechanical part of the engine. Most often the culprits are:

• 🔄 Timing belt/chain — slipped a few teeth or broke
• 💥 Low compression in cylinders (wear of piston rings, valves)
• 🛠️ Damaged flywheel - cut crown teeth
• 🔗 Seized camshaft or crankshaft (rare, but it happens)

How to diagnose?

• Check coincidence of timing marks (if the belt has slipped, the engine will not start or will run intermittently).
• Measure compression in cylinders (norm: 10–14 bar, spread between cylinders no more than 1 bar).
• Listen to the starter sound: if heard metallic grindingThe flywheel may be damaged.

Please note: if the engine starts and immediately stalls, this could be a sign depressurization of the intake manifold or throttle valve malfunction. In this case, an error may appear on the dashboard P0505 (idling system malfunction).

8. External factors: weather, fuel, human factor

Sometimes the reason for an unstable start lies not in the car, but in external circumstances. Let's look at the most common ones:

• ❄️ frost — the oil thickens, the battery weakens, the fuel in diesel engines becomes waxy
• 🌡️ heat — overheating of the fuel pump, evaporation of gasoline in the fuel line
• ⛽ Bad fuel — diluted gasoline, water in diesel, Wrong fuel (filled with 92 instead of 95)
• 🚗 Human factor — they forgot to press the clutch, the alarm was on, the battery died due to the headlights being left on

What to do?

• B frost: use winter oil (0W-40, 5W-30), warm up the battery, add anti-gel to the diesel engine.
• B it's hot: Avoid refueling in the middle of the day (fuel evaporates), check the operation of the radiator fan.
• If you suspect bad fuel: drain it, flush the system, replace the filter.

If the car does not start after refueling, try adding octane booster (for gasoline) or cetane corrector (for diesel). In extreme cases, you will have to drain the fuel and flush the system.

⚠️ Attention: If you accidentally uploaded gasoline to diesel (or vice versa) don't try to start the car! This will lead to damage to the fuel injection pump, injectors and catalyst. Immediately evacuate the car to a service station to flush the system!

FAQ: Answers to frequently asked questions

The car does not start after washing the engine - what to do?

Most likely, water got on electrical contacts (starter, ignition coils, generator) or in air intake. Try:

1. Dry the engine with a compressor or hairdryer (do not use open fire!).
2. Check fuses - they could burn out from a short circuit.
3. If the car still won't start, check spark plugs - they could get wet.

In the future, avoid high-pressure washing of the engine and use hydrophobic sprays to protect electronics.

Why doesn't the car start after a long period of parking (a month or more)?

The reasons may be as follows:

• 🔋 The battery is low (even a new battery loses its charge when idle).
• ⛽ Gasoline has evaporated from the fuel line (especially in hot weather).
• 🛢️ Piston rings are coked (if the oil is old).
• 🐭 Wiring damaged by rodents (check the engine compartment).

What to do: charge the battery, check the fuel system, change the oil and filters. If the engine does not start, you may need to decarbonization.

The car starts only with the pusher - what is the reason?

If the engine starts only from a tug or pusher, but does not start from the starter, the reasons may be as follows:

• 🔋 Weak battery — there is not enough current to crank the starter.
• 🔄 Starter malfunction - does not develop the required speed.
• ⚡ Ignition problems — at low starter speeds the spark is weak.
• ⛽ Air leak — the engine starts only with high pressure in the cylinders.

Start by checking battery and starter. If they are ok, diagnose ignition system and intake tract tightness.

Can an alarm block the engine from starting?

Yes, and this is one of the most difficult to diagnose reasons. Modern alarm systems (eg StarLine, Pandora) may block launch due to:

• 🔑 Immobilizer malfunction (does not recognize the tag).
• 📡 Interference from other electronic devices (for example, proximity keys).
• 🔋 Discharged key fob or a faulty control unit.

What to do: try to turn off the alarm (usually there is an emergency shutdown with a hidden button), check the key fob, reset the settings. If it doesn't help, take the car to auto electrician.

Why doesn't a diesel engine start when cold, but starts normally when hot?

For diesel engines this is classic problemrelated to:

• ❄️ Thickened fuel (summer diesel in the cold).
• 🔥 Faulty glow plugs (does not warm up the combustion chambers).
• ⛽ Air leak in the fuel system (fuel does not enter the injection pump).
• 🛢️ Worn fuel injection pump (does not create the required pressure when cold).

Solution: use winter diesel fuel, check the glow plugs (their resistance should be 0.5–6 ohms), bleed the fuel system.