Modern vehicles are full of sensors and actuators trying to milk out as much horsepower as possible from ingested fuel while emitting less and less harmful gases. One essential and easily forgotten sensor is the crankshaft speed and position sensors.
The sensor feeds this information to the ECU and Powertrain Control Module. They use it to make necessary operational conditions modifications for better engine performance.
Faulty or not, information from the crankshaft position sensor messes up many engine management calculations. The effects of such a failure range from the mild rough running engine to severe when the engine doesn’t run at all.
Where is the Crankshaft Position Sensor Located
The sensor sits on the engine block facing the crankshaft’s timing rotor in most engines. Most manufacturers ensure that it’s well protected from impact, humidity, and dust.
The chances of the sensor failing or malfunctioning are very low unless it is a factory defective unit or your vehicle is very old.
ProTip: Crankshaft position sensors are either inductive (analog wave) or hall effect sensors (digital square wave)
What Makes Crankshaft Position Sensors Fail?
Even though these sensors rarely fail, they will die on you or give faulty readings under the following circumstances.
You Develop a Wiring Problem
Damaged wiring or faulty ground could throw off your crankshaft position sensor’s signal, even if the problem isn’t directly linked to the sensor’s wiring.
Firstly, the sensor will malfunction if its wiring is faulty. It won’t deliver a signal to the ECU effectively.
It can also fail if another component in your vehicle’s wiring mess with the CAN bus or different voltage rail stabilities.
Since the sensor transmits precise AC pulses, any signal problem that could lead to fluctuations in voltage might induce false counts or miscounts into the system.
An Overheating Engine
Most crankshaft position sensors are either made of a plastic polymer or have some plastic components.
The sensor is designed to tolerate normal engine temperatures. It will start disintegrating or distorting as the temperatures creep up in an overheating engine.
Since the sensor is on the engine block, it directly soaks up all that heat from an overheating engine.
Signs that You Have a Bad Crankshaft Position Sensor
Luckily, a handful of things will happen in your engine and on your error reporting system once the crankshaft sensor fails or starts sending corrupted data. These include:
A Check Engine Light
Since the Powertrain Control Module always expects a signal from the crankshaft position sensor, it will throw an error code if it gets none.
An OBD-II scanner will pull the error code P0335. This stands for ‘Crankshaft Position “A” Circuit Malfunction.”
The PCM throws the error when it can’t detect a signal from the crankshaft position sensor. This could either mean the sensor is faulty or there is a problem with the wiring to the sensor.
Other possible error codes include:
- P0335-P0339
- P0385-P0389
- P0016-P0019
The Engine Won’t Start Easily (or at all)
Modern vehicles rely on the crankshaft position to make basic calculations. It’s a foundational input without which an engine won’t operate.
If the sensor fails, your engine might not even start at all. If it fails with the engine running, it could continue running rough but won’t turn over again.
A sensor sending corrupted data will make it harder to start the engine, and if you get the engine running, it won’t be as smooth as it should be.
Your Engine Will Idle Rough
Your engine isn’t optimized for comfort and performance without an effective crankshaft position sensor.
It can’t determine how much fuel to inject and ignite properly. This will result in erratic performance that translates into excessive engine vibration.
Reduced precision in engine operation becomes more evident with the engine idling since it doesn’t have high RPMs to compensate and even out the jerks.
The vibrations could worsen when you add some load to the engine, such as turning on the AC or putting the transmission in gear.
A Misfiring Engine
With no foundational information to help the PCM calculate critical air-fuel mix and ignition timing, you will get a lot of misfires from your engine.
While misfires can be caused by faulty spark plugs, inadequate fuel injectors, and other things, your crankshaft position sensor can also be a culprit.
A misfiring engine will throw a check engine light. In most cases, the check engine light will be flashing when running a misfiring engine.
Apart from that, the engine will vibrate and shake violently. You will feel like you are driving over corrugations.
Get your vehicle inspected immediately and the misfire fixed. Keeping on using it could result in more expensive damage.
Stalling Now and Then (Especially Under Load)
With the PCM and ECU guessing how much fuel your engine needs and when to inject it, your engine’s performance will be highly compromised.
All those misfires will add up. You will not be running efficiently and producing as much horsepower or torque as you should.
A weak engine stalls easily, especially when under heavy load and at low RPM. You will experience unexpected stalls when:
- Starting out
- Slowing down while still in gear
- Idling with the AC on
- Accelerating hard
- Crawling up a steep hill or rough terrain offroad
Jerky and Rough Acceleration
Another easy-to-note impact of a faulty crankshaft position sensor is jerky and uneven acceleration.
It will be different from the lag or slow transmission shifts and be more uneven edges that seem to mirror your engine’s RPM.
The ECU and PCM will have difficulty maintaining even and efficient power output. The engine could also surge and drop erratically.
Note: Even if you are not in gear, revving your engine will result in the same impact. There will be erratic changes in engine speed that don’t mirror your throttle input.
Your Gas Mileage Will Drop
With all the inefficiency, lack of data, and erroneous data, your fuel injectors will most probably be working overtime. They will be dumping unusable fuel into the cylinder.
Since you are getting less bang for your fuel, you will end up with terrible engine performance and worse gas mileage than ever.
Can I Keep on Driving With a Bad Crankshaft Position Sensor?
No. Driving with a bad crankshaft position sensor is bad for your engine – significantly if the symptoms have escalated to misfires, stalling, and shaking.
It could lead to a cascade of failures that will damage other things in your engine, making them harder to fix.
Different cars handle crankshaft position sensor failure differently.
- An engine will run erratically with no signal
- Run erratically on bad signal without flagging it
- Ignore no signal or bad signal and revert to a predetermined primary data set that though not efficient, could keep a well-maintained engine running for ages
Replacing the sensor is always wise regardless of how gracefully your engine handles the failure. Some of the secondary issues that could arise if you ignore them include:
- Fouled spark plugged (running too rich)
- Damaged fuel injectors (running too rich)
- Damaged ignition coils (running too rich)
- A clogged EGR valve (running too rich)
- An overheating engine ( if you run too lean for too long)
- Blown head gasket (if the overheating is terrible)
- Clogged or damaged DPF and Catalytic Converter (running too rich)
Can You Bypass a Crankshaft Position Sensor?
Though possible, it takes a lot of effort and time. You could dedicate this effort to replacing the sensor.
Bypassing will involve installing a signal generator that mirrors what the sensor will transmit when working fine.
Since there is no known benefit in bypassing the sensor other than avoiding replacing it, it would be best to get a replacement.
How Much Does it Cost to Replace a Crankshaft Position Sensor?
Most crankshaft position sensors cost under $100. Depending on your vehicle model, the cost will vary and can skyrocket if you drive a high-end unit.
As for labor costs, this will vary depending on how skilled your mechanic is and the actual position of the sensor. Some engines will have it in a highly accessible spot, while others will hide it behind heavy components like the gearbox.
If you are handy and the sensor isn’t hidden behind components, you can do the replacement in your garage. Otherwise, you will have to pay a pro half an hour to an hourly fee to get the job done.