6 Symptoms of a Johnson Outboard Optical Sensor Failure

Normally, a Johnson outboard engine can experience a bad optical sensor. The owner would have to deal with something so meticulous. Because the symptoms of a running-out trigger on a Mercury outboard are frequently linked to other faults, finding one can be challenging. 

One of the most common symptoms of Johnson optical sensor failure is having trouble starting the engine. But a single symptom won’t be enough to detect a faulty mercury outboard’s trigger. 

In this article, we will discuss all the possible symptoms and causes of Johnson’s optical sensor failure. We’ll also cover the potential solutions to this problem. So, we hope this article will help you figure out and troubleshoot a bad trigger.

How Do You Know If the Johnson Outboard Optical Sensor Is Bad?

A bad Johnson optical sensor (also called a trigger) can be defined by multiple symptoms. But these symptoms are also very common for other car problems. 

So, when you experience the following symptoms at a time, it’s better to check the optical sensor of your car. 

Symptom 1: No Spark

This is the most common symptom of a bad optical sensor on a Johnson outboard engine. 

The optical sensor in an outboard engine sends a signal to the switch box or power pack to release a spark or voltage to the ignition coil.

So, if the optical sensor goes bad, it will fail to send the signal, resulting in intermittent or no spark. 

Symptom 2: Hard Start

If you don’t run your outboard motor for a while, it may have some difficulties or take extra time to get started. 

Though it can happen for various reasons, optical sensor failure is also a strong suspect for this problem. 

If the optical sensor has no spark or low power, it will cause a hard start. It can also cause the engine not to start at all.  

Symptom 3: Engine Stalling

Because of a faulty optical sensor on a Johnson Mercury outboard, the engine may start stalling repeatedly or running rough. So, it’s better to check the optical sensor when it occurs. 

Disconnect the sensor and crank your outboard motor. If it works, then the trigger has surely become damaged.

Symptom 4: Bad Noises

There can be different causes behind this problem. But a faulty optical sensor can also be responsible for the issue. 

When the engine doesn’t get enough power because of a bad optical sensor, it may intermittently crank or make unusual sounds. 

Symptom 5: Poor Fuel Economy

As we mentioned earlier, a failing optical sensor on a Johnson outboard engine can cause low sparks or no spark in the car. When there is no spark in the car, it will hamper the engine’s combustion system.

Thus, it will result in low fuel economy. Fuel consumption can also increase if your Johnson outboard motor is idling for a long time due to a bad trigger. 

Symptom 6: Engine Misfires and Missing

The Mercury outboard’s trigger or optical sensor is connected to a Johnson outboard motor’s ignition coil, spark plugs, and combustion system. A bad optical sensor can cause damage to the spark plugs or ignition coil.

Thus, faulty spark plugs or ignition coils may cause engine misfires, missing sparks, and other issues.

6 Possible Causes of Optical Sensor Failure on a Johnson Outboard

Like other auto parts, the optical sensor on an outboard engine also tends to be damaged. The optical sensor on a Johnson outboard engine can fail for the following reasons: 

  • The optical sensor has been running for a long time.
  • Internally damaged optical sensors 
  • Damaged wires or connectors
  • Wear and tears 
  • Old or faulty wire insulation 
  • Inconcity of internal temperature 

Replacement and Repair Costs of a Johnson Outboard Bad Optical Sensor

The repair cost of a bad optical sensor on a Johnson outboard engine depends on how much it has gone bad and how long it takes to be repaired. 

Usually, the labor cost of fixing a Johnson outboard’s optical sensor is 100 or 125 dollars per hour. 

But if you need to replace the bad optical sensor,  a new Johnson outboard optical sensor will cost between $150 and $320. 

Thus, the replacement cost of a Johnson outboard’s bad optical sensor is around $250 to $450. Let’s figure out this cost at a glance: 

Labor costNew Optical Sensor costTotal cost

However, this cost may increase or decrease depending on your location, as the labor cost varies from country to country, area to area. 

Moreover, in the winter, the replacement cost of an optical sensor or trigger is far less than in the summer.

Tips for Maintaining the Johnson Outboard Optical Sensor to Prevent Future Failures

Experiencing and trying to fix an error on your Johnson outboard is truly bad luck. 

But proper maintenance can protect the sensor from further failures. Here are some possible precautions to prevent future damages: 

  • Install a new optical sensor before the old one gets too old. 
  • Make sure that the insulation of the cables has been properly done. 
  • Inspect the cables and connectors to ensure they are not broken, corroded, or bent. 
  • Don’t let the crankcase oil be too dirty. 
  • Change the oil when it’s required.

Frequently Asked Questions

Though we know the possible symptoms and precautions of an optical sensor, fixing a bad Johnson outboard optical sensor may require more information than that. Here are some of them:

How do you test a Johnson outboard optical sensor?

This optical sensor has two sets of wires with brown, purple, and white colors. Gradually connect the two probes of a multimeter from brown to purple, white to brown, and purple to white. The sensor is defective if these three readings are not identical.  

What does an optical sensor do on a Johnson outboard engine?

The main purpose of an optical sensor on a Johnson outboard engine is to send the cylinder and crankshaft locations to the power pack. It also monitors the direction of engine rotation and prevents sparks if the direction is not right.

Can you drive with your Johnson outboard engine with a bad optical sensor?

Yes, you may still be able to drive your Johnson outboard engine with a faulty optical sensor, but it shouldn’t be recommended. Driving an outboard with a bad optical sensor will cause engine stalls, misfires, and even hard starting or rough driving. It can also increase fuel consumption.

How do you replace a bad Johnson outboard optical sensor?

First, diagnose the optical sensor properly before you assume it is bad. Then, locate the optical sensor under the Johnson outboard engine’s flywheel. Now, remove it using a flywheel puller and install the new one.


A defective Johnson outboard’s optical sensor will lead to poor engine performance and damage the power pack, ignition coil, and spark plugs. So, one shouldn’t take another chance, as it is relatively cheap and easy to solve.  

So, it’s better for you to replace the bad optical sensor if you experience any symptoms. But before installing a new sensor, make sure that you have diagnosed the optical sensor properly. 
However, don’t damage other outboard parts while replacing the sensor yourself. Otherwise, take your outboard to a garage and have a professional mechanic fix it. But don’t use any aftermarket item to shake off the engine’s performance.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *