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What are the Symptoms of a Bad Crankshaft Sensor | Masters of Motion
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What are the symptoms of a bad crankshaft sensor?

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Sensors Vehicle Electronics & Engine Management Need to Know Technicians 4 min read

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The crankshaft sensor is an important piece of kit to keep the engine running correctly. On this page we’ll highlight common causes of crankshaft sensor failure, why it happens and how to fix it.

What is a crankshaft sensor and what does it do? 

A vehicle’s crankshaft sensor or CKP sensor contributes to the precision timing of a finely tuned engine. It monitors the position and rotational speed of the crankshaft, so the engine control unit (ECU) can adjust its calculations in the fuel injection timing and elsewhere.  

The crankshaft’s speed and position must be closely monitored to properly maintain a four-stroke engine. Without this input from the sensor, the engine may not even start. Therefore, the sensor output is an essential part of the process. 

Some engines that don’t have a knock sensor use the crankshaft sensor to perform the same function – find out more about that function with this expert insight from Delphi. 

What causes a crankshaft sensor to go bad? 

There are several factors which can cause a crankshaft sensor to fail.  

In crankshaft sensors which contain magnets, a build-up of dirt on the magnet can block the sensor and prevent it from seeing the engine’s spin. Another factor in the lifespan of a crankshaft sensor is its age – the magnet in the sensor loses its pull over time, which means it grows less capable of providing accurate signals to the ECU. Faulty, lose or damaged wiring can affect the sensor’s ability to send signals accurately to the ECU.  

The crankshaft sensor is a clever piece of kit, but it can be fooled. If the gear which the sensor is tasked with observing suffers damage, the sensor can’t be sure of what it’s looking at, which can cause confusion as it sends mixed signals to the ECU. This will likely bring up an engine check light. 

There’s also the chance the sensor is damaged by a hit from another component inside the engine such as the crankshaft pickup, or by road debris. If that component is repaired but the engine is still having difficulty starting, the unnoticed damage to the sensor could be what’s causing it. 

Check out the range of crankshaft sensors available from Delphi. 

What are the symptoms of a bad crankshaft sensor? 

A vehicle diagnosed as having a faulty crankshaft sensor is likely to exhibit a number of problems with the engine and overall performance. Look for the following warning signs to confirm what’s troubling the vehicle. 

Engine light is showing 

(Note: If the vehicle has a camshaft sensor you might get no engine light, and no fault on the diagnostic tool. The ECU doesn’t know if the engine is specifically not starting, or is just at rest. Check the RPM to be sure. Newer cars have two camshaft sensors so they should be able to see if the camshaft has an issue.) 

If the sensor isn’t relaying information to the ECU, or what it is sending appears troubling, the ECU will respond by turning on the engine light – your cue to assess what’s ailing the vehicle. The engine light could be caused by a range of different issues aside from the crankshaft sensor. A diagnostic tool can help you to identify if the sensor is the part that’s causing concern. 

Engine is having trouble starting 

The crankshaft sensor is responsible for keeping a close eye on the position and speed of the crankshaft when starting the engine. So if it’s unable to relay information back to the ECU, the engine may not start. If the engine is currently running, you may not even notice an issue here regardless of whether or not there’s an engine light – the sensor uses an algorithm to estimate where the crank has spun to based on previous knowledge, so the engine won’t shut off due to electronic override. It’s only when you key off the engine and try to restart the vehicle later that an issue will occur. 

Limp mode 

A bad crankshaft sensor isn’t the only reason a vehicle may experience higher than usual fuel consumption, but it’s nonetheless one of the tell-tale signs. With a faulty crankshaft sensor, the engine may go into limp mode if it’s still running. This means the fuel injectors won’t act as efficiently in their role, meaning reduced performance and an overall worse fuel economy. 

Buy quality crankshaft sensors from Delphi. 

What happens if you drive with a bad crankshaft sensor? 

If a crankshaft sensor develops an issue while the engine is running, although a specific fault may cause engine misfire, there won’t necessarily be a problem. But in light of some of the symptoms described above, a vehicle probably won’t start at all with a faulty crankshaft sensor. A car may go into limp mode while driving, to reduce the chances of further damage. 

What to do if a crankshaft sensor is faulty 

If a faulty crankshaft sensor is suspected, or a similar issue is causing engine problems, an inspection will be required. The sensor should be tested for faults – this can be done with both a visual inspection and using a oscilloscope. 

If there is an issue with the sensor, we would recommend replacing the part entirely. It’s a relatively simple job – locate the sensor (usually close to the flywheel or on the timing cover side of the block), remove electrical connections and replace with a new part. The plug connection should be replaced at this time too – it’s subjected to the elements more than most parts, so could be in poor condition and is also worth a visual inspection as you’re replacing the sensor. 

Suffering from a faulty crankshaft sensor? 

Once it’s stopped, a vehicle with a bad crankshaft sensor is unlikely to get going again. Having checked the symptoms of a faulty crankshaft sensor against other potential causes, the recommended course of action is to carry out a replacement. Delphi stocks OE car parts – check out the range of crankshaft sensors. 

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