Saturday, February 25, 2017 Detailed Auto Topics
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Detailed Topics

Not cranking and not starting may seem like the same thing. They are very different situations, from a standpoint of repair. This Detailed Topic is designed to help those, without special equipment or training, understand the engine cranking system.  A later topic will address the issue of not starting.

What happens when the key is turned

When the key is turned, the starter-motor should crank the engine. After a second or less the engine starts to run. This may appear to be one thing, but it is two. It is possible for a vehicle to not-crank, or it can crank, but fail to start. The distinction seems subtle, but it is huge when trying to solve no-start problems.  One issue is with the vehicle cranking system, and the other is an engine running problem.

When the engine does not crank

To crank means to turn the engine, so it will start

The word 'crank' comes from vintage automobiles that used a crank to spin the engine. Today, a cranking engine makes a particular sound. The sound is a battery-powered motor turning the engine. When no sound, a strange noise, one or more clicks are heard the problem is normally in the cranking system. This includes the starter, cables, battery and several switches. An engine that cranks as usual, means these parts can be assumed okay. If this is the case, and the engine will not start, the problem is not in the cranking system.

How should a starter sound 

  Normal engine cranking sound

  Weak battery sound

Preliminary quick tests of the cranking system

A quick test, when the engine does not crank, is to try to blow the horn, while holding the key in the crank position. If the horn blows normally, it shows the battery and cables are usually okay. This means either the starter has failed or something is keeping current from reaching it. When the horn does not blow, or sounds weak, look at the volt meter in the dash. A good battery will register well above 12 volts. Less than twelve volts present, shows a discharged battery. No voltage reading means either the battery is dead or the cables are not making contact.

Three quick tests to find the reason it does not crank

A voltmeter is needed to test the components of the cranking system. Basic instructions for voltmeter tests are in the Tips on Automotive Electrical Testing Detailed Topic.

Basic electrical checks for no crank

1. The voltage between the battery terminals should be checked to see if it is more than twelve-volts.  More than twelve volts between the battery post does not mean the battery is okay. Less voltage means the battery should be tested and charged before preceding. If testing shows the battery is fine, but it is discharged, there is a problem in the charging system or a parasitic draw.  Even though a battery produces twelve-volts while unloaded, does not mean it has the capacity to crank the engine.  An engine that cranks slowly, a loud click or multiple clicks can indicate a battery with low capacity.  A battery load test, with specialized equipment can be used to determine the battery capacity.  Testing the voltage between the terminals, when the key is turned to crank, gives an indication of battery condition.  You may also turn the headlights on to load the battery.  Dim lights or any reading that drops below twelve-volts indicates a need to check the battery further..

2. With the battery confirmed okay, check between the positive post and the engine block. Low or no voltage shows a bad negative cable or connection.  Any battery terminal that can be moved by hand, is too loose to properly conduct current.  Temporary, bolt-on battery cable ends are notorious for causing cranking problems and should be replaced with proper crimp on terminals.  Any corrosion at the terminal will increase resistance and decrease the available current.  Corrosion is a symptom of battery leakage.  Cleaning the terminal will only give temporary results, until the actual problem is resolved.

3. The last test is for full voltage at the large top terminal on the starter solenoid, if it can be reached. This is the large connection at the end of the heavy positive battery cable.  This cable is often red in color, for identification.  A Lack of voltage at this point, means the positive cable or one of the connections to it has failed.

If all three of these test indicate okay, the problem is likely in the starter, solenoid or something is interrupting the start command.  In the next Detailed Topic, how these functions and how they are tested, is covered.





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