An internal combustion engine must have a functional crankshaft position sensor. Otherwise, the engine control unit won’t receive accurate information about the position and speed of the crankshaft. The crank sensor is used in both petrol engines and diesel engines. This article explains the working, function, and signs of a bad crankshaft position sensor.
What is a Crankshaft Position Sensor?
A crankshaft position sensor is an electronic device used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. The engine control unit (ECU) uses this information to control the fuel injection or the ignition system timing and other engine parameters.
Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on petrol engines.
The crank sensor can be used in combination with a similar camshaft position sensor to monitor the relationship between the pistons and valves in the engine, which is particularly important in engines with variable valve timing. This method is also used to “synchronize” a four-stroke engine upon starting, allowing the management system to know when to inject the fuel.
It is also commonly used as the primary source for the measurement of engine speed in revolutions per minute.
Crankshaft Position Sensor Working
The crankshaft position sensor is positioned so that teeth on the reluctor ring attached to the crankshaft pass close to the sensor tip. The reluctor ring has one or more teeth missing to provide the engine computer (PCM) with the reference point to the crankshaft position.
As the crankshaft rotates, the sensor produces a pulsed voltage signal, where each pulse corresponds to the tooth on the reluctor ring.
The PCM uses the signal from the crankshaft position sensor to determine at what time to produce the spark and in which cylinder. The signal from the crankshaft position is also used to monitor any of the cylinder’s misfires.
If the signal from the sensor is missing, there will be no spark, and fuel injectors won’t operate.
The two most common types are the magnetic sensors with a pick-up coil that produces A/C voltage and the Hall-effect sensors that produce a digital square wave signal as in the photo above.
Modern cars use the Hall-effect sensors. A pick-up coil type sensor has a two-pin connector. The Hall-effect sensor has a three-pin connector (reference voltage, ground, and signal).
Function of Crankshaft Position Sensor
The main function of the crankshaft position sensor is to determine the position and/or rotational speed (RPM) of the crank. Engine Control Unit uses the information transmitted by the sensor to control parameters such as ignition timing and fuel injection timing.
In diesel engines, the sensor will control the fuel injection. The sensor output may also be related to other sensor data, including the cam position to derive the current combustion cycle; this is very important for starting a four-stroke engine.
Sometimes, the sensor may become burnt or worn out – or just die of old age at high mileage. One likely cause of crankshaft position sensor failure is exposure to extreme heat. Others are vibration causing a wire to fracture or corrosion on the pins of harness connectors.
Many modern crankshaft sensors are sealed units and, therefore, will not be damaged by water or other fluids. When it goes wrong, it stops transmitting the signal which contains the vital data for the ignition and other parts in the system.
Bad Crankshaft Position Sensor Symptoms
As the crankshaft position (CKP) sensor goes bad, it gives one of the below-given signs:
- Weak Engine Performance
- Excessive Engine Vibrations
- Check Engine Light
- Trouble Starting Car
- Engine Misfire
- Engine Stalling
1) Weak Engine Performance
With a bad crankshaft position sensor, your engine control unit won’t know the correct position of the crankshaft or cylinders. This will cause a delay in the control unit’s ability to sustain the operation and performance of the engine.
During this delay, there will be moments of hesitation each time you step on the gas pedal a little bit harder. Sometimes it won’t respond at all. This can be very dangerous on a road that requires you to go faster without hesitation.
2) Excessive Engine Vibrations
If your engine has a faulty crankshaft position sensor, then it isn’t optimizing any performance. Even worse, it might be utilizing incorrect readings to determine fuel and ignition timing. If the ECM doesn’t time things correctly, you’re in for a bumpy ride.
Even worse, the problem is only going to get worse until you fix it, and it’s only a matter of time until further damages occur.
3) Check Engine Light
The engine control unit stays in constant communication with the crankshaft position sensor. If there is ever something wrong with the sensor, then the computer will receive improper information regarding the speed of the crankshaft and its position.
This will cause functionality problems with the engine, resulting in the Check Engine warning light activating on the dashboard. In fact, this should be one of the first symptoms of a bad crankshaft position sensor. P0335 and P0336 are two common trouble codes that may be displayed.
4) Trouble Starting Car
If your defective crankshaft position sensor is extremely out of sync, you might have trouble getting your vehicle started. Furthermore, you might have difficulty keeping it started.
This is usually only a problem when the problem has persisted for some time, and you likely have various other underlying issues too. Moreover, it’s not usually a problem if you have a check engine light and the ECM has defaulted to predetermined values.
Instead, it’s a problem when the crankshaft position sensor delivers inaccurate readings, and your ECM doesn’t realize it.
5) Engine Misfire
A crankshaft position sensor that fails will not be able to accurately transmit data regarding the piston position to the engine control unit. This often results in a misfire inside one or more of the chamber cylinders.
Sometimes a bad spark plug can do this, too, but if you are experiencing any of these other symptoms, don’t rule out the possibility of a bad crankshaft position sensor.
6) Engine Stalling
You may be driving along one day and have your engine suddenly stop running. This is engine stalling, and it can happen quite frequently when you have a bad crankshaft position sensor.
If you don’t replace this sensor soon, your engine will eventually stop working. Then you will have no choice but to get your vehicle towed to a mechanic, so the sensor can be replaced.
Crankshaft Position Sensor Function
The purpose of the crankshaft position sensor is to measure the position of the crankshaft. It might sound redundant, but it’s one of the most critical sensors in your vehicle. The crankshaft position sensor sends these measurements to the ECM, and the ECM uses them to optimize the rest of your vehicle’s timing.
If the crankshaft position sensor fails, then the ECM reverts to default values. While these values keep the engine running, you’ll likely notice various performance issues.
Crankshaft Position Sensor Location
Your vehicle’s crankshaft position sensor is located near the bottom of the engine by the crankshaft. That makes sense because it’s the crankshaft position sensor’s job to measure the crankshaft location.
When you’re trying to track down the crankshaft position sensor, look towards the engine’s bottom, generally on one of the sides. Since the sensor is so far down in the engine, it can be hard to locate and even harder to remove and replace if you have a faulty one.
Crankshaft Position Sensor Replacement Cost
If you experience at least two or more of the above symptoms, then you probably have a bad crankshaft position sensor. The only way to know for sure is to bring your vehicle to a licensed mechanic and have them diagnose the problem for you.
The replacement cost of the crankshaft position sensor is anywhere from $120 to $300. The cost of the part itself will be around $75 to $120. The cost of the labor will be anywhere from $45 to $180.
How To Make a Temporary Fix for Crankshaft Position Sensor?
However, if you cannot go to the auto repair shop, you can apply the temporary remedies below. Especially in the case of a sudden car stall, you can follow the below-given steps to make a temporary fix for the crankshaft position sensor:
1) Restart the engine
If you are driving, the car shakes and jerks, or the check engine lights up; you should pull over to the curb. Stopping the vehicle, turning off the engine, waiting for the engine to cool down, and restarting the machine can help reduce shock in your car.
2) Filling up fuel
If the car suddenly stops because the ECU does not supply enough fuel to the cylinder, you can fix it by filling it up with fuel.
3) Disconnect the CKP sensor
If your car has failed to start from scratch, you should try disconnecting the crank sensor.
First, you need to find the location of the CKP sensor according to the instructions (near the camshaft).
Then you remove the CKP sensor connector and restart the car. If you’re lucky, the car will start up using the car’s default mapping.
In case the car still does not start, you should find a way to replace the car’s CKP sensor.
Crankshaft Position Sensor Replacement
When the crankshaft sensor fails, your engine may run poorly or may not run at all. There are a few steps to be taken to replace the crankshaft position sensor which is the same for all engines.
- To replace the crankshaft sensor by yourself, you’ll need a few materials and tools such as a floor jack, jack stand, ratchet and socket set, cleaner, and a new crankshaft sensor.
- Initially, you need to secure and prepare your vehicle by using jacks and jack stands.
- Once you are done with the setup, it is time to disconnect and unplug the sensor’s electrical connector from the engine wiring harness.
- Now, you need to locate the sensor, which is mounted near the crankshaft pulley. Using the proper sized socket and ratchet handle, you can easily remove the sensor bolt.
- After that, gently lubricate the O-ring on the new sensor to make it easier to install.
- The next step is to firmly twist the new crankshaft position sensor and reinstall the bolts.
- At this time, plug the new crankshaft position sensor into the engine wiring harness. Use a clip to prevent the sensor from unplugging itself during operation.
- Lower the vehicle carefully and remove the jack stand.
FAQ Section
What is a Crankshaft Position Sensor?
A crankshaft position sensor is an electronic device used in an internal combustion engine to monitor the position or rotational speed of the crankshaft.
What causes the crankshaft sensor to go bad?
There are a few things that can cause the crankshaft position sensor to fail, including damage, debris, and faulty circuitry.
The excessive build-up of heat in the engine can lead to crankshaft sensor damage by melting the plastic covering—circuitry Problems. A faulty voltage or loose, worn-out, or damaged wiring can disrupt the signals sent to and from the crankshaft sensor, causing it to have issues.
What are the signs of a bad crankshaft shaft position sensor?
As the crankshaft position sensor goes bad, it gives one of the below-given signs:
- Engine Stalling
- Poor Engine Performance
- Engine Misfiring
- Trouble Starting Car
- Excessive Engine Vibrations
- Check Engine Light turns On
Where is the Crankshaft position sensor located?
The crankshaft sensor is usually located near the bottom of the block, toward the front of the engine. In most cases, you’ll find it behind the harmonic balancer. In some vehicles, you might find the crankshaft sensor behind the timing cover, near the bottom of the block, though this is rare.
What happens when a crank sensor goes out?
If your crankshaft sensor is not working properly, the motor control unit in your vehicle won’t be able to execute the changes to the fuel injection or to the spark timing whenever the engine speed climbs.
Can a car start without a crankshaft sensor?
The crankshaft position sensor is the most important of all engine management sensors, and the engine will absolutely not run without it.
What sensor would stop a car from starting?
A crankshaft position sensor (crank sensor) is an important device measuring the engine RPM and tracing the crankshaft position. The car won’t start if the crankshaft position sensor doesn’t work properly. The crank sensor can fail, or its wiring can get damaged. This may cause the car to stall or not start.
