Engine Won't Crank Over with the Starter

Troubleshooting is required to find the real cause

These diagnostic instructions apply to both gas and diesel engines. If your engine will not crank over when you turn the key or does so intermittently, then check the following in the order listed. Remember to always start with the simple and inexpensive first and then move on to the more complex/expensive. You can not believe how many times people have had their starter motors replaced only to discover it was a bad switch or poor electrical connection! 

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Problem & Solution

Common among these chassis:

Classic Sedans
Ponton
R107
W108 W109
W110 W111 W112 Sedan
W111 W112 Coupe
W113
W114
W115
W116
W123
W124
W126
W201

1. Check your battery and battery connections first. Use a meter to check battery voltage across the terminals. You should have at least 12.3 volts. If low charge the battery. If the battery will not hold voltage overnight with it completely DISCONNECTED then replace the battery. Check the ground connections at the battery negative terminal and from the engine to the body. The engine ground cable is located either on the left or right side and is attached to the transmission bell housing. Remove the battery post cables and clean thoroughly. To read more about maintaining your battery review our technical help section.

WARNING: If you are having a problem keeping a full charge in your battery ( and have confirmed your battery is ok by proper testing) then replace the voltage regulator. This is the number one reason for loss of charge to the battery and the part is cheap and easy to replace!  Fair warning.......

2. Check your starter motor by powering it directly. This will bypass the two switches that control the starter circuit and help to determine if your starter it working properly. You will need a long jumper wire either 12 or 14 gauge wire . First check to see if your car has a starter terminal box that you can access. These are either located near the battery or down on the fender well across from the alternator. There will be three wire connections. The smaller of the three is usually the one going to the starter solenoid. You need to connect 12 volts directly to the small wire connection on the starter. This activates the solenoid and engages the starter. With your car in park and the ignition key off, use your jumper wire to connect the positive post on your battery directly to the solenoid itself or the wire terminal we discussed earlier. If the starter will not turn over then you have a starter problem. 5 times out of 10 replacing the solenoid will solve the problem. If the starter only spins over but does not engage the flywheel then the solenoid is most likely the problem. You can remove the starter and take it to an electrical shop for testing. They can let you know if the motor itself is bad or just the solenoid.

To purchase a new starter solenoid see related products below:

3. Check your electrical switches.  If you have done the above and are still having problems you will have more troubleshooting to do. There are two switches that control the starter circuit. One is on the back of the ignition lock assembly and is of course controlled by the key. If you can wiggle your key to get the starter to engage then I recommend you replace the ignition switch. We have new switch installation kits available.  See below.

A second switch - called the neutral safety switch is located on your transmission right behind the shift lever (located on the driver side). The purpose of this switch is to prevent you from starting the car unless the shift lever is in neutral or park. Try starting the car in neutral to see if that helps. If you have bad shift bushings in your shifter linkage that can raise havoc with this switch. Try wiggling the shifter in park while turning the key at the same time. If you get a starter contact in either case above then replace the neutral safety switch.

Our shift bushing kit with special tool makes it easy to install the bushings from under the car. 

FOLLOW UP: For additional help in repairing your problem see the related products listed below.