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P0318 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

Trouble code P0318 is defined as “Rough Road Sensor A Signal Circuit.”

Meaning

If you have a P0318 trouble code appear on your OBD II scanner, it means that your powertrain control module (PCM) has noticed a change in your crankshaft position. It essentially tells your car that you are experiencing uneven or rough driving.

Causes

A code of this type may be stored and the service engine soon lamp will come on any time the PCM recognizes a sudden fluctuation in the position of the crankshaft. This will occur while driving on uneven or rough surfaces. 

Keep in mind that some vehicles require several failure cycles before the service engine soon lamp will come on. You might also have disconnected, missing, or defective rough road sensors that could be causing this issue. This can also be caused by a defect in other rough road detection hardware, within the vehicle.

Symptoms

Symptoms may include a misfiring engine or hesitation, followed by a stored trouble code and a Check Engine light that will not turn off. You may also find that your traction control or anti-lock brake systems are affected as well.

Diagnosis

There are several steps that you should follow in order to properly diagnose a P0318 trouble code. 

Start your diagnosis with a careful visual inspection of all rough road sensors, electrical connectors, wiring harnesses, and hardware. Always repair or replace any defective components, or any disconnected or damaged wiring or connectors first. If the wiring connectors, harnesses, and hardware on the rough road sensor system seem to be in good shape, then connect your scanner and record all freeze frame data and stored trouble codes. Remember to always diagnose and repair codes in the order in which they are stored.

If your problem persists, inspect your connector faces for debris, dirt, and corrosion. Next, replace or repair wiring, components, and connectors if they are in poor shape. Using your digital volt/ohmmeter, test the ground signals and voltage at the sensor connector. If both the voltage and ground signals are present, then reconnect your sensor and test the signal wire at the connector while recreating a rough road condition. If the sensor indicates it has power and ground but provides no signal voltage or the signal voltage fails to change with you changing conditions, you know you need to replace the sensor.

However, if everything checks out, then you may have a faulty control module. Please note that an experienced technician with a specialized scanner may be able to determine the exact malfunction more easily than someone with a digital volt ohmmeter and code reader. 

Keep in mind that diagnosing a P0318 trouble code using your digital volt ohmmeter would involve probing thousands of circuits, which is incredibly time-consuming and tedious. Additionally, one misplaced probe could destroy your expensive control modules. Destruction of a control module could require reprogramming your vehicle.

Common mistakes

A common mistake is to replace your wheel speed sensors, crankshaft position sensors, and camshaft. This will not necessarily solve the problem. This is why it is so important to use the proper diagnostic equipment, or to take your vehicle to a professional technician who will diagnose the problem for you.

How serious is this?

Because this problem can affect your brakes, it should be treated very seriously. As soon as you see this code, either take your vehicle into a professional technician or begin doing research to fix the problem yourself.

What repairs can fix the code?

You or your professional technician may need to replace your rough road sensor. However, this can be determined only after a careful and thorough inspection. A P0318 code is best left to a professional technician because he or she will have the tools to properly diagnose the problem.

Related codes

None listed.

Conclusion

A P0318 trouble code is serious, and one that is best diagnosed and fixed by an experienced technician. There are a lot of various problems and issues in various parts of the vehicle that may be responsible for causing this code to register on an OBD II scanner. A skilled technician should have all of the equipment and experience they need to properly diagnose and fix this trouble code without damaging the vehicle. They will also be able to accomplish this in a much shorter amount of time than someone who is inexperienced with technical automotive work.