Why Won't My Engine Turn Over?

Updated on December 10, 2017
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

If the engine won't turn over, check the battery and starting system.
If the engine won't turn over, check the battery and starting system. | Source

You turn the key, and you hear nothing; or even if you hear sounds from the starter, the engine itself doesn't get going—doesn't rotate. Whatever the ultimate cause, the engine fails to turn over because the starter motor is failing to turn the crankshaft.

Possible Reasons Why Your Car Engine Won't Turn Over When You Turn The Key

  • Low or no battery power
  • A bad battery
  • Issues with the starter motor or solenoid
  • Starting circuit problems
  • Faulty ignition switch
  • Engine mechanical problems

Tests You Can Do to Find the Fault Yourself

Here are some simple tests that can guide you to locate the fault. In most cases, with little mechanical experience, you'll be able to fix the problem on your own, using a few simple tools you may already have in your toolbox. In rare cases, you'll find you have an expensive repair on your hands.

Begin with a few simple checks and tests you can do in a few minutes before getting into more involved, but easy, diagnostic procedures. The section headings below describe most common symptoms your engine may show when refusing to rotate. Head over to the appropriate section, but don't forget to check other sections that may help you as well.

Index
1. Make Sure Your Car Is in the Right Gear
2. Try to Pin It Down to the Battery or the Starter
3. Check the Battery
4. What to Do If You Can Hear the Starter Motor Spinning
5. What to Do If You Can Hear the Starter Motor Humming
6. What to Do If You Can Hear the Starter Motor Grinding
7. Quick Starter Circuit Checks
Make sure the transmission is in Park or Neutral.
Make sure the transmission is in Park or Neutral. | Source
Clean battery terminals and posts.
Clean battery terminals and posts. | Source

I. First: Make Sure Your Car Is in the Right Gear

When you are in a hurry, it's easy to overlook the obvious.

If you have an automatic transmission, make sure it is in Park or Neutral when trying to start the engine. Otherwise, the transmission neutral safety switch (in older models) or range sensor will prevent you from starting the engine, for safety reasons.

2. Try to Pin It Down to the Battery or the Starter

Battery problems are a frequent source of starting system issues. A classical symptom is chattering noises or no noises at all when trying to start the engine.

But before you begin checking for battery issues, do this quick test to pinpoint the problem area.

  • Ask an assistant to turn on the headlights. They should be bright.
  • Have the assistant try to start the engine while you watch the headlights.
  • If you see the headlights dimming, head over to Quick Starter Circuit Checks, section 7 below.
  • If the headlights don't dim, continue with the following battery checks.

3. Checking the Battery

First, make a visual inspection to determine the condition of the battery.

  • Check the battery case for cracks, bulges, and other signs of damage.
  • Check battery terminals for corrosion.

It is common for corrosion to build up around the terminal and the battery posts, and if it gets bad enough it will interrupt the flow of electricity.

If there's corrosion:

  1. Detach each terminal. Disconnecty the negative (black) cable first, followed by the positive (red) cable, to prevent shorting out the electrical system and damaging components.
  2. Mix a tablespoon of baking soda with 8oz of warm water.
  3. Use a small soft brush to apply the solution to the terminals and battery posts, being careful not to allow the mixture to seep under the battery caps, if the battery has them.
  4. Wipe clean the batter case, posts and terminals using a shop rag.
  5. Connect the battery terminals starting with the positive cable followed by the negative cable to prevent an electrical short.
  6. Try starting the engine.

If removing corrosion doesn't fix the problem:

  • Check the terminals for tightness and damage
  • Inspect the cable attached to the terminals and make sure it doesn't have broken wires.

Now make sure the battery has enough power to operate the starter motor.

Even if your battery is putting out some power, if it isn't fully charged it may not have enough power to get the starter going.

If you suspect you have a bad battery, you can take it to your local auto parts store and have them charge it and check battery performance.

But you can also check battery power yourself. Here's a quick way to do this if you don't have a digital multimeter:

  1. Turn the ignition key to the On (Run) position, without trying to start the engine.
  2. Switch on the headlights or the windshield wipers.
  3. If the headlights are too dim or don't come on, or the wipers move slowly or don't move at all, your battery is likely undercharged or discharged. If possible, slow-charge the battery to improve electrolyte chemical action.
  4. If the battery has removable caps, make sure the electrolyte in each cell reaches the bottom of the filling ring before charging the battery.
  5. If your battery doesn't have removable caps (maintenance-free battery) check the charge indicator "eye" on the top cover (sight glass), A dark green eye means your battery is fully charged; a dark means the battery needs charging; and a yellow eye means the battery needs to be replaced.

Another, and more precise, way to check the battery at home is with a multimeter, preferably one with at least 5% accuracy. You can get a inexpensive multimeter on Amazon that is precise enough to do these tests.

Check battery power with a multimeter:

  1. Set your multimeter to 20 volts on the direct current (DC) scale.
  2. Turn the headlights or the heater blower on.
  3. Touch the positive (+) battery post with the red probe of your meter and the ground (-) battery post with the black probe.
  4. Your multimeter should read 12.3 or 12.4 volts. The lower the voltage, the lower the charge.

Testing battery cables

You can use your multimeter to see if the battery clamps or wires are interfering with the flow of power. Repeat your battery voltage test, but this time, in step 3, instead of touching the battery posts touch the battery cable clamps, and then repeat the test, if possible, touching the battery cable wires. Compare your readings. If your readings differ, check the battery cable clamps or the cable themselves, as necessary. Check for corrosion, looseness or damage.

When the starter motor operates but the engine doesn't rotate, electric current is reaching the starter motor but the engagement mechanism may not be working.

The starter engagement mechanism may be stuck.
The starter engagement mechanism may be stuck. | Source

4. What to Do If You Can Hear the Starter Motor Spinning

Sounds can give you an important clue about what is going on in the starting system.

When you hear the starter motor spinning—going on and on as you hold the key in the "start" position—but the engine itself doesn't come on, that means electric current is reaching the starter motor but for some reason the starter is not engaging with the engine.

When it works normally, the starter's engagement mechanism pushes the pinion gear (Bendix) forward so that it meshes with the large ring gear around the edge of the flywheel. One reason the starter won't work is that this engagement mechanism is stuck.

You can try to unstick the Bendix:

  • If your car has an automatic transmission, try striking the starter motor (softly, not hard) with a hammer or wrench and try starting the engine again.
  • If it doesn't work, try it again, but this time have an assistant try to start the engine as you hit the starter motor.
  • If you have a car with a manual transmission, put the car in 4th gear and rock it back and forth a few times, and then try starting the engine.

Once you get your starter motor unstuck, try replacing it as soon as possible, because it may get stuck again.

If "unsticking" the starter doesn't work, you'll need to make a closer inspection of the starter motor.

  1. Set your transmission to Park (automatic) or Neutral (manual).
  2. Set the parking brake.
  3. Block the rear wheels with wooden blocks to prevent the vehicle from moving.
  4. Raise the front of the vehicle, if necessary, to gain access to the starter motor.
  5. Visually check that all the connections are clean and tight.
  6. If you don't see any problems with the electrical connections, remove the starter motor. Some motors may use one or more shims for proper installation. Take note of their position so that you reinstall them in their original place.
  7. Inspect the pinion gear for wear or damage. You can also take the motor to your local auto parts store and have them test the motor.

Check the flywheel for bad ring gear.
Check the flywheel for bad ring gear. | Source

Checking the Flywheel Ring Gear

If you get this far, you may want to check the ring gear around the edge of the flywheel (see image above) for missing teeth or other damage that may prevent the starter motor from engaging properly. To check the entire ring gear, you may need to rotate the engine manually.

  • Use a breaker bar and socket to rotate the crankshaft from the crankshaft pulley center bolt at the front of the engine.
  • Set the transmission to Neutral if you have a manual transmission.
  • You may need to raise and safely secure the front of your vehicle on jack stands.
  • Block the rear wheels with a couple of wooden blocks.
  • As you rotate the crankshaft, have someone look at the ring gear.
  • If the crankshaft seems hard to rotate, try removing all the spark plugs. Don't force the crankshaft.

Watch the next video for some tips about checking a seized engine.

5. What to Do If You Can Hear the Starter Motor Humming

A humming noise when you turn the ignition key may also point to a faulty engagement mechanism. The starter motor driver is unable to mesh the pinion gear to the flywheel.

  • Raise the front of the vehicle, or gain access to the starter motor.
  • Check that all electrical connections are tight and clean.
  • If the connections are fine, remove the starter motor.
  • Take the starter motor to your local auto parts store for a quick diagnostic.

6. What to Do If You Can Hear the Starter Motor Grinding

If you hear grinding when you turn the key, the problem could be with the starter motor itself, the starter solenoid, or the flywheel ring gear, or there could be more than one problem present. Make the following checks:

  1. Make sure the starter motor mounting bolts are tight. Loose bolts will prevent the pinion gear from meshing properly with the flywheel ring gear, causing the grinding noise.
  2. If the mounting bolts are tight, remove the starter motor and check the pinion gear (Bendix) at the front of the starter and check it for wear or damage.
  3. Check the ring gear around the edge of the flywheel for wear or damage. You may need to manually rotate the engine for this. See the last section in part 3 above.

Parts of the Starter

A faulty starter solenoid can prevent the starter motor from operating properly.
A faulty starter solenoid can prevent the starter motor from operating properly. | Source

7. Quick Starter Circuit Checks

If you've decided that the battery is fully charged, and you don't see mechanical problems with the starter, you may want to investigate electrical problems in the starter circuit. It's not common, but the failure to turn the motor over could be due to a circuit open, or similar problems that prevent current flow, for example a loose or corroded connection or a failed component.

These quick circuit checks can point you in the right direction. The next series of tests can help you check for current feed and solenoid operation. Go over the section that corresponds to your particular issue.Make sure the battery is fully charged before you begin the tests.

You'll need a digital multimeter (DMM). If you don't have one, you can buy a quality, inexpensive unit DMM from Amazon.

Before starting these checks, disable the ignition system. You may unplug the ignition coil cable from the distributor and ground it using a jumper cable, or remove the ignition or fuel system fuse.

When you are testing the starting system, locate and remove the igniton or fuel system fuse.
When you are testing the starting system, locate and remove the igniton or fuel system fuse. | Source

If you hear no sound at all coming from the starter solenoid when trying to start the engine:

1. Disconnect the control circuit wire (small wire) from the back of the starter solenoid; sometimes this is marked with the letter "S".
2. Check the wire and terminal for corrosion, looseness, or damage.
3. To check for feed voltage, connect your voltmeter between the negative battery post (black meter lead) and the control circuit wire end (red meter lead).
4. Ask an assistant to try to start the engine.

  • If your meter indicates no voltage, check for an open in the part of the circuit leading to the control circuit terminal, including the ignition switch. You may need your vehicle repair manual to locate components and wires in that part of the circuit for testing.

If you can hear sounds coming from the starter motor when trying to start the engine:

1. Disconnect the control circuit wire from its terminal at the back of the starter solenoid.
2. Use a jumper wire to connect the control circuit terminal on the starter solenoid and the positive terminal on the battery.

  • If you hear a solid click, the solenoid is working. Continue with the next step.
  • If you hear a chattering sound or a series of weak clicks, check for a bad solenoid ground. Make sure the solenoid is properly mounted and the strap between the solenoid and starter motor is not damaged and is making good contact. If the solenoid is properly grounded, replace it.

3. Reconnect the control circuit wire to its terminal.

4. Do a voltage drop check.

Checking a solenoid that is mounted on the starter:

  • Connect your multimeter between the battery cable terminal on the back of the starter solenoid and the strap that connects the solenoid to the starter motor.
  • Ask an assistant to try to start the engine.
  • If your meter reads more than 0.2 Volts, install a new solenoid.

Checking a remote mounted solenoid:

  • Connect your multimeter across the two battery cable connections.
  • Ask an assistant to try to start the engine.
  • If there's more than 0.2 Volts, make sure the cables are connected properly and clean. Otherwise, install a new solenoid.
  • Disconnect the control circuit wire from the solenoid.
  • Check resistance between the control circuit terminal and the solenoid mounted bracket.
  • If your reading is over 5 ohms, replace the solenoid.

Source

If your engine will not rotate, more often than not, you can diagnose and repair the fault yourself. Before sending your car to the shop, try the simple tests outlined here to save time and money.

Questions & Answers

    © 2017 Dan Ferrell

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