Symptoms of Bad Solenoid

Updated November 21, 2016

For most automobile users, the ignition key turns and the engine starts---that's all they care to know about it. Underneath that simple action, the solenoid unit is actually a complicated mechanism that manages a large amount of electrical energy in the process of starting an engine. But, the solenoid is susceptible to damage, corrosion and overload that may lead to the need for replacement. Proper maintenance and prevention will protect the solenoid and prolong its life.

What is a Solenoid?

The solenoid of an automobile is associated with the starter system and transfers an electric current into the starter motor to set the engine into operation. When the ignition key is turned, current is released from the battery and travels along an insulated wire into the solenoid. The solenoid then releases a small plunger that creates a connection between two internal electrical posts, sends the current down another wire to the starter and forces the starter motor to spin.


The solenoid is located under the hood of a car or truck near the starter unit. It can easily be located on any vehicle by following the path of the positive red cable from the battery to its direct connection to the solenoid. A cable then runs from the solenoid for transmission of electrical current into the starter. Access to the solenoid and starter is best achieved from under the vehicle. Some solenoid models are integrated directly into the starter units.

Bad Solenoids

The symptom of a bad solenoid includes a rapid clicking sound indicating it is receiving too little power from the car battery. This lack of power may be from a low battery or corrosion of the battery cables causing the engine to not start. Corrosion is also possible in the internal solenoid connections, or a blocked plunger may lead to the solenoid being flooded with power and burning out the internal connections to damage the unit. Clicking on attempted ignition should be a warning to have the starter system checked.

Failure Prevention

Proper engine maintenance and tune-ups can keep a solenoid from going bad. Due to the solenoid's position under the engine, it is more prone to contact with corrosive materials, and may lead to the need for replacement. To reduce the likelihood of failure, battery connections should be tightened and cleaned at approximately every 3000 miles, wires checked for tightness, and a visual inspection of the solenoid and starter performed by a trained mechanic every 15,000 miles. Any strange noises on ignition, especially clicking of any type, should be a warning to have the unit checked.

Repair Cost

The cost of average solenoids is not very high, usually between £22 and £48. Labor is the main cost and can run anywhere from £65 to £162 depending upon the service centre or region of the country where the work is performed. If the solenoid is integrated directly into the starter, the cost will generally double for both parts and labour.

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