We all know how frustrating it can be when you try to turn on your car in the morning and it refuses to start. It can be any number of reasons or problems, and some of them you can sort by yourself, and for some, you will need professional help. However, it is always helpful to be able to diagnose what is wrong with the car quickly and accurately. Not only will you know what to do next and if you can fix it yourself but it can also save you a lot of time and money. To help with that, we’ve created this quick guide including all you need to know about how to start a car with a bad crankshaft sensor, whether you should try it or not, and if it’s even possible at all.
How a Crankshaft Position Sensor Works and What It’s Used For?
To adequately understand what a crankshaft position sensor (CKP) does, it’s important to understand what a crankshaft actually is. To put it simply, the crankshaft is basically a shaft on which the pistons are attached. It is mounted on the lower portion of the engine block, spinning as the pistons move up and down and transferring the energy created to the transmission. For a more in-depth overview of crankshafts and how they do their thing, click here.
A CKP sensor, as its name implies, monitors the crankshaft’s exact position during the combustion cycle and, makes sure that the engine is rotating at a constant speed. When it senses that the engine is not rotating evenly, the PCM will detect and record a misfire-related DTC code.
The crankshaft position sensor’s job is vital for the engine’s proper operation. The Powertrain Control Module uses the data sent by the CKP sensor to correctly time the injection time and duration, the ignition timing, and sometimes other variables depending on the car model.
To correctly identify and troubleshoot a faulty CKP sensor, it’s important to keep in mind that this type of sensor comes in different shapes and forms. As opposed to O2 sensors, for example, which pretty much always look and work based on the same basic principle, CKP sensors may differ greatly. Of course, it goes without saying that different operation principles will also require different testing procedures. The most common types are inductive, Hall Effect, magnetoresistive, and optical. Since this article is not meant to be an in-depth review of all the different types of CKP sensors, we won’t cover each of them in detail. However, if you plan to test the CKP sensor on your car, make sure to check the right testing procure in your car’s repair manual first.
Most Common Symptoms of a Bad CKP Sensor
To identify a failing CKP sensor as quickly as possible, you’ll need to first be aware of what happens when the PCM loses the sensor’s signal. To help you with that, here’s a quick list of the most common symptoms related to a faulty crankshaft sensor.
- Crank/No Start condition: This condition happens when the engine cranks but fails to start, even after multiple tries.
- Immediate stalling of the engine: The car does start, usually after an extended cranking time but stalls right away or moments after.
- Lumpy idle: If the sensor is failing intermittently, the PCM will default to factory settings because of the incorrect readings, compromising fuel delivery. This condition will usually cause misfires and jerky acceleration.
- Flashing check engine light: Once the PCM loses the CKP sensor’s signal or if the readings are out of the normal threshold, the check engine light will start to flash and a DTC code will be recorded.
Common Crankshaft Position Sensor-related DTC Codes
Once you suspect your car might suffer from a faulty CKP sensor, the quickest way to confirm it is to scan your car for codes. It’s not uncommon for fuel and ignition system problems to cause the same symptoms as a faulty crankshaft sensor. To confirm your hypothesis, read the DTC codes recorded in the PCM with an OBDII scan tool. The DTC codes present will usually tell you where the problem is coming from right away.
There can be several issues with the sensor itself, so it is essential to know what is actually the problem with the sensor (timing, correlation, circuit, position, coil…) so you know what needs to be done to fix it.
Here’s a non-exhaustive list of some of the DTC codes related to a faulty crankshaft position sensor:
P0016 to P0019
- P0016 – Crankshaft Position – Camshaft Position Correlation (Bank 1 Sensor A)
- P0017 – Crankshaft Position – Camshaft Position Correlation (Bank 1 Sensor B)
- P0018 – Crankshaft Position – Camshaft Position Correlation (Bank 2 Sensor A)
- P0019 – Crankshaft Position – Camshaft Position Correlation (Bank 2 Sensor B)
Each of these codes is related to a correlation problem between the crankshaft and the camshaft position sensors. Such a condition is detected when both sensors don’t send the same data or when the data stream is lost on either one of them. It’s often used as a way to ensure that both sensors are in good working condition. For example, if the CKP sensor indicates that the cylinder 1 is at the Top-Dead-Center position while the camshaft sensor indicates that it’s at Bottom-Dead-Center, a correlation code will be recorded.
Each DTC code points to a specific sensor to inform you as precisely as possible which one might be faulty. Your car may or may not be equipped with 4 sensors so make sure to check in your car’s repair manual to know which one’s which and where it’s located.
P0335 to P0339 – P0385 to P0389
- P0335 – Crankshaft Position Sensor A Circuit Malfunction
- P0336 – Crankshaft Position Sensor A Circuit Range/Performance
- P0337 – Crankshaft Position Sensor A Circuit Low Input
- P0338 – Crankshaft Position Sensor A Circuit High Input
- P0339 – Crankshaft Position Sensor A Circuit Intermittent
- P0385 – Crankshaft Position Sensor B Circuit Malfunction
- P0386 – Crankshaft Position Sensor B Circuit Range/Performance
- P0387 – Crankshaft Position Sensor B Circuit Low Input
- P0388 – Crankshaft Position Sensor B Circuit High Input
- P0389 – Crankshaft Position Sensor B Circuit Intermittent
These codes are related to a problem in the CKP sensor’s electrical circuit. A wire may be cut or skinned creating a short to ground condition, the coil inside the sensor might be open or short, etc. In all cases, it will have something to do with the electrical circuit.
- P1345 – Crankshaft Position-Camshaft Position Correlation
This error code is a manufacturer-specific trouble code, meaning that it doesn’t apply to all vehicles makes. Rather, it only applies only to specific manufacturers such as Audi, GM (Chevrolet/GMC), Isuzu, Lexus, Mazda, Toyota, and Volkswagen. It’s meaning is usually the same as P0016 to P0019 generic codes but the exact description may differ from manufacturer to manufacturer.
- P1374 – 3X Reference Circuit
This code is also manufacturer-specific and usually comes up on Chevrolet vehicles. Other car manufacturers may use it too but I’ve only seen it on Chevy cars before. The 3x reference signal is a signal used to estimate the engine RPM and to time the opening of injectors. To put it shortly, if anything happens with the 3x reference circuit, a P1374 will be recorded.
Can I Start a Vehicle with a Bad Crank Sensor?
Whether or not you can start a car with a bad crank sensor will depend on the car model. Some vehicles, and especially older ones with simpler engine electronic systems, only use the CKP sensor to monitor the engine for misfires. On these cars, it might take a little more cranks to start the engine, the check engine light might start flashing or, at least illuminate, but it should start just fine.
With modern vehicles, however, it might not be possible since they rely heavily on electronics. In most cases, the PCM may cancel the ignition or fuel injection system to prevent the engine from starting.
How To Start a Car with a Bad CKP Sensor?
In the worst-case scenario, if you really needed to start the vehicle anyway, there are always some tricks you can try. Some vehicles have crankshaft sensor that can be reached, often mounted on the front underside of the engine block, near the timing chain (or belt) cover. How to start a car with a bad crankshaft sensor will often depend on the car model but you can unplug the CKP sensor connector and try to start the engine again. In this case, the PCM receiving no reading from the sensor will try to compensate by using its default mapping. Sometimes, and if you’re lucky, the engine might start.
That’s really a long shot, though. In most cases, a car with a bad crankshaft sensor will simply not run at all. It might also start and stall right away. When it happens, you’re better off just calling for a tow truck.
Crankshaft sensors are quite simple in essence and don’t need to be replaced that frequently. However, just like any other electronic component, a short or open circuit may happen in the coil. This usually happens once water can enter the sensor causing the internal component to rust. In that case, replacing it is the only suitable option. Luckily, crankshaft position sensors are usually inexpensive parts available in all major auto parts stores. Omitting to replace it at the first signs of failure can quickly leave you stranded. If you find yourself in a situation when your car won’t start, and you have all the symptoms of a faulty crankshaft sensor, make sure to inspect and troubleshoot the problem as soon as possible to prevent any additional damage and a higher repair cost.
Also, never forget that the easiest way to replace a CKP sensor is usually to follow the manufacturer’s procedure. When in doubt, make sure to get your hands on your car’s repair manual, to learn more about the testing and troubleshooting process as well as the correct removal and replacement procedure.