Car Won’t Start After Replacing Crankshaft Position Sensor? 8 Reasons And Solutions To Fix It!

Car Won't Start After Replacing Crankshaft Position Sensor
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If your vehicle runs inconsistently and doesn’t give a proper response to the throttling and running rough, then probably you have the issue in one of the sensors in the powertrain systems.

If you have a bad crankshaft position sensor, then the car won’t start since it either wouldn’t sense the engine RPM or feed the wrong input to the engine PCM which may cut off the power supply to the fuel pump when the engine is cranked.

Often the issue is due to a malfunctioning crankshaft position sensor. But while replacing it, there are certain procedures and precautions that you need to follow.

The reason for the issue of car won’t start after replacing crankshaft position sensor would be due to improper sensor installation, bad replacement crankshaft sensor, damaged crankshaft sensor connector, and wiring, weak battery and terminals, bad PCM, or the issue may lie at other engine systems like fuel, ignition, and air intake systems.

Have you replaced crankshaft position sensor and now the car won’t start? Then you are in right place to look out for possible root causes and solutions to fix the problem.

Functions Of Crankshaft Position Sensor

The crankshaft position sensor plays an important role in measuring the crankshaft’s speed and position to ensure timely ignition and fuel ignition in the combustion chamber.

The crankshaft position sensor is usually located onto the engine close to the engine reluctor wheel tooth which has no. of teeth arrangements on its periphery.

The reluctor wheel has no. of tooths around the periphery and it has one empty slot to identify the location of the piston top dead center (TDC).

Three different types of crankshaft position sensors are typically used. One is the hall effect type and the second one is an inductive type and the last one is optical type sensors.

Hall effect sensor

In the case of the hall effect sensor, it has a powerful magnet within the main body housing, whose magnetic field is continuously exerted over the sensing element located beside the magnet.

When a tooth comes in front of the sensing element, the magnetic field exerted on the sensing element will get disturbed and the resistance across it gets disturbed and this change in resistance or voltage is sent to the engine PCM (Power Control Module) for identifying the speed and position of the crankshaft.

Inductor type sensor

The inductor type sensor has a winding coil surrounding the magnet instead of a sensing element.

Whenever a tooth of the reluctor wheel passes this sensor, the magnetic field gets disturbed and this generates an EMF in the winding coil which produces fluctuating pulses which would be sent as output to the engine PCM for processing crankshaft position and speed data.

Optical type sensor

In the case of optical type sensors, instead of a reluctor wheel with tooths, they have a slotted wheel with a slot through which the light rays travel and hit the photodiode.

Whenever the slotted wheel rotates along with crankshaft, the photo diode continuously gets an intermittent light signal from the light source depending upon the slot locations.

This intermittent signal produces a voltage fluctuation in the photodiode and the signal is fed to the engine PCM.

Whenever the empty slot of the reluctor wheel comes in front of the sensor, a zero signal will be sent to PCM and the engine reads this as the position of piston TDC to finalize the ignition timing and fuel injection.

Any malfunctioning in the crankshaft position sensor will lead to incorrect crankshaft speed and position interpretation and the vehicle would run rough and would not respond properly to throttling or the car won’t start at all.

Car Won’t Start After Replacing Crankshaft Position Sensor? 8 Reasons And Solutions To Fix It!

There are a lot of sensors that take part in ensuring the effective functioning of the engine systems.

To confirm that the issue of car not starting or improper vehicle performance is due to a bad crankshaft position sensor, you would need to look out for the below symptoms,

  1. The vehicle suddenly stops while driving, but when you crank it starts again with ease.
  2. The vehicle doesn’t start in a moist or cold environment but when checked at normal ambient conditions, the vehicle starts without any issue
  3. When the vehicle needs longer cranking time to start, then probably the crankshaft position sensor is faulty.
  4. When you try to crank, the engine cranks but the vehicle doesn’t start, then you need to look for a bad crankshaft position sensor.
  5. Modern vehicles with OBD support can easily identify a bad crankshaft position sensor just by connecting an OBD tool and it may highlight the P0335 error code.

There are certain procedures and sequences to be followed while replacing a bad crankshaft position sensor.

But there are situations where the car won’t start after replacing crankshaft position sensor, if you fail to adhere to procedures.

Below is the list of a few causes and solutions to fix them.

Improper crankshaft sensor installation

Typically, a crankshaft position sensor has a mounting slot for varying mtg centre distances between mounting points depending on the vehicle model.

While installing the sensor, you need to ensure the typical position of the crank or piston with respect to the sensor, otherwise, the car won’t start after replacing crankshaft position sensor.

The sensor location is kept considering the ignition timing advance and fuel injection timing so that before the piston reaches the TDC the ignition is usually done for ensuring maximum engine power.

These things won’t be possible without with precise location of crankshaft position sensor with reference to the empty slot on the reluctor teeth on crankshaft.

But if the sensor has a slot for mounting, how will you ensure precise control? For that, you need to follow the below procedure.

  1. Disconnect the crankshaft position sensor and the electrical connector.
  2. Remove the starter, if it is coming in the line with the crankshaft position sensor. Depending upon the vehicle model, it may vary.
  3. Remove the mounting bolt and crankshaft position sensor.
  4. Install the new crankshaft position sensor.
  5. Typically, the sensors are located matching with the twentieth tooth starting from the empty slot (no tooth).
  6. But here the catch is that the piston also needs to be at the top dead center while installing the crankshaft position sensor. But how will you ensure that the piston position is at TDC? Here we go!
  7. Generally, besides the crankshaft position sensor, there is a bolt (usually M10) that is fastened to the crankcase. Simply, we need to remove the bolt and replace it with a special timing tool that looks like a bolt but with some extra length than the original one.
  8. Once you fit the special bolt, rotate the crankshaft pulley clockwise until it gets stuck with the special bolt. You will arrive at a position where further rotation of the crankshaft pulley becomes difficult. This position is the piston TDC.
  9. Some reluctor wheels have a marking on the twentieth teeth for matching with the crankshaft position sensor for ease of fixing the sensor with respect to the piston TDC.
  10. Once the sensor position is fixed, tighten the mounting bolt.

Bad replacement crankshaft sensor

Sometimes the replaced crankshaft position sensor turns out to be a faulty one and the car won’t start even after replacing the crankshaft position sensor and we scratch our heads to troubleshoot other areas unnecessarily. Ensure that the crankshaft sensor is a good one.

Hence it is essential to test and check the new crankshaft position sensor whether it is performing as intended or not! 

Damaged crankshaft sensor connector

Sometimes, the crankshaft position sensor may be good but the connectors for fitting the sensor gets damaged and it doesn’t allow the output signal from the sensor to the engine PCM, hence the car won’t start after replacing crankshaft position sensor.

In some cases, a dirty or corroded connector pin also would not send signal data to PCM for processing since there will not be proper electrical conductivity across the corroded connector pins.

So, it is advised to inspect the sensor connectors and replace connectors with a new one if found damaged.

Improper wiring

If the wiring which is connecting the ECU to the crankshaft position sensor is damaged, broken, or eventually continuously grounded, then also the car won’t start even after replacing crankshaft position sensor.

For example, in certain cases, the wiring comes in contact with a heat source like exhaust parts and it gets melted hence the crankshaft position sensor gets disconnected from the PCM and the car will not start even after crankshaft sensor replacement.

Foreign matters accumulation on sensor

If there is an entanglement of any foreign matters between the sensor and the reluctor wheel teeth, then the crankshaft position sensor may not be able to identify the crankshaft position and speed and it won’t be able to feed the signals to the engine PCM.

Hence the PCM won’t activate the ignition system and the fuel pump thereby leading to the problem of the car won’t start after replacing crankshaft position sensor.

Weak battery and terminals

Have you disconnected the battery negative terminal before working on the problem?

Have you reconnected the battery terminals after sensor replacement?

These are obvious questions, but many times we forget to reinstate the battery to its original condition.

If you have already ensured battery terminal connection, then when did you change the battery?

Is your battery due for replacement? A weak battery would cause the car not to start even after replacing crankshaft position sensor.

Often due to multiple terminal disconnections, the terminal threads get worn out or get stripped, and even after full tightening, the terminal nuts remain loose.

This terminal loose connection causes the intermittent power supply to the engine parts and you may be wondering why the car won’t start after replacing crankshaft position sensor?

Hene it is necessary to carefully inspect the battery and its terminals and replace them with a new one.

Bad PCM

It is possible that the engine PCM (power control module) would go bad after some period of operation and it may not be able to process the input signals which come from various sensors including the crankshaft position sensor.

If the PCM itself goes bad, the car won’t start after replacing the crankshaft position sensor.  

You need to identify and troubleshoot the issue with the PCM and fix or replace it.

Issue in other engine systems

Even after checking the above troubleshooting points and ensuring that the parts are running fine, if you could not get the RPM signals or crankshaft position sensor signal through the live data scanner, then the problem may lie with other vehicle systems.

You may need to troubleshoot fuel system, ignition system, or air intake system.

It is also recommended to check preliminary items like vehicle fuses of different parts or main relay, and fuel pump relay because these are the parts that generally blow out or malfunction if there is a huge current drawn by the load parts like the fuel pump.

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How To Test Crankshaft Position Sensor?

Typically, an inductor-type sensor has three wiring connections for sensor operation.

They are PCM ground wiring, 12V reference wiring, and 5V signal wiring.

A fault at any one of the wiring or if the wiring is wiggling in and out of the socket then it would make the car not to start after replacing the crankshaft position sensor.

It is obvious that, if the connector itself is faulty replacing the cranks position sensor is not going to help.

You would follow the below procedures to test the connector or wiring of the hall effect type crankshaft position sensor.

Step 1

Take a test light or a multimeter.

Connect one of the leads to the battery positive and the other one to the ground terminal going to ECU.

If the light glows, then the wiring and terminal are good.

Step 2

Connect one of the leads to the battery negative and the other end to the reference 12 V.

Here also the light shall glow which indicates that this wiring and terminals are ok.

Step 3

Connect a multimeter or test light to the 5V output signal and it shall read 5 V or the light shall glow.

This would indicate whether the signal wiring is also effective or not.

Step 4

Use jumper wire between the 12V reference wiring and the 5V signal wire or you may connect one lead to the battery negative and the other to the 5V reference signal terminal.

While you do make and break contact with the signal wire, you shall be able to listen to the fuel pump running sound.

You need to carefully observe whether the simple touching of lead to the sensor signal terminal is sufficient or pressing of the terminals is required to activate the ignition system and supply power to the fuel pump.

Often if the connector terminal is loose, the crankshaft position sensor may send intermittent signals to the PCM (ECU) and hence fuel pump would run erratically and the car won’t start after replacing crankshaft position sensor.

To precisely troubleshoot the crankshaft position sensor, you would need to crank the engine and use an oscilloscope to continuously monitor the sensor signals, where you can check for any sudden drop in the sensor signal output (ignore the signal drop corresponding to the empty slot of the reluctor wheel tooth)

You may also test with a scan tool that gives the engine RPM output corresponding to the sensor signal data.

If there is a sudden drop in the signal data or engine RPM output and later if it regains, then the problem is either within the crankshaft position sensor or its wiring or at connectors.

Conclusion

The crankshaft position sensor plays an important role in communicating the engine speed to the ECU for deciding the fuel injection and ignition timing.

If you follow the above steps seriously, we would be able to pinpoint the problem area.

A new crankshaft sensor is not supposed to cause the car starting problem unless it is tested ok and its performance is good.  

If the issue is not due to the crankshaft position sensor, connector, and its wiring, then something might have happened accidentally, or intentionally while working on the system which might have caused the car not to start after replacing crankshaft position sensor.

This may include forgetting battery connection after sensor replacement work, damaged battery terminal threads, or accidentally disengaging some other engine-related sensors.

Other causes of the car won’t after replacing crankshaft position sensor may be related to one of the engine systems like fuel, ignition, or air intake system.

We have tried to collate all reasons for the issue of a car won’t start after replacing crankshaft position sensor. Hope with this info in hand, you would be able to troubleshoot this issue and a save few bucks.

Happy Motoring!

 

References

https://www.dodgeintrepid.net/threads/car-wont-start-after-cam-crank-sensor-replacement.23639/

https://www.grandprixforums.com/3-1l-v6-lho-lg8-/37477-replaced-crankshaft-position-sensor-now-wont-start.html

 

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