What happens when the crank sensor goes bad?

When a crankshaft position sensor fails, the engine may fail to start, stall unexpectedly, or run rough because the engine computer loses timing information.

The crankshaft position sensor (CKP) monitors the crank’s position and rotation speed to time ignition and fuel injection. A faulty CKP or its wiring can trigger a check engine light, cause intermittent stalling, and create drivability problems. This article explains what happens, how to recognize it, and how it is diagnosed and repaired.

What the crankshaft position sensor does

The CKP provides the engine control unit with real-time data about the crankshaft’s angle and RPM. This information is crucial for synchronizing spark timing and fuel delivery. When the sensor falters, the ECM may lose synchronization, leading to misfires, poor performance, or the engine not starting at all.

Symptoms of a failing CKP sensor

Overview of common signs

The following symptoms are frequently associated with a failing crankshaft position sensor. Not every vehicle will exhibit all of these, and some symptoms can overlap with other problems.

• Engine won’t start or cranks but won’t fire


• Engine stalls or dies while running


• Rough idle or repeated misfires


• Intermittent stalling or hesitation during acceleration


• Tachometer flickers or drops to zero while cranking or running


• Check Engine Light is on, often with CKP-related codes (e.g., P0335, P0336, P0337, P0338)


• Reduced power or entry into limp mode in some vehicles


• Backfiring or mis-timed ignition at higher RPMs

These symptoms can appear separately or together, and they may be intermittent if the sensor is failing or the wiring is damaged.

Causes and risk factors

What's commonly behind a bad CKP sensor

Several issues can lead to a CKP problem. Understanding common causes helps with both diagnosis and prevention.

• A failing CKP sensor itself due to age, heat, or contamination


• Damaged or corroded wiring and connectors in the CKP circuit


• Problems with the reluctor ring (the toothed wheel near the crank) or crankshaft timing gear


• Improper installation or misalignment of the sensor


• Electrical interference or a faulty power/ground supply to the sensor


• PCM or BCM faults in rare cases, though mechanical and wiring issues are far more common

Addressing these factors often requires a combination of wiring repair, sensor replacement, and, in some cases, timing-related adjustments.

How it’s diagnosed

Diagnostic approach and tests

Diagnosing a CKP fault involves confirming that the sensor and its circuit are functioning correctly and ruling out related systems. The steps below are typical for many modern vehicles, though exact procedures vary by make and model.

• Retrieve trouble codes with an OBD-II scanner and review freeze-frame data for CKP-related codes (e.g., P0335, P0336, P0337, P0338)


• Inspect CKP wiring, connectors, and the harness for damage, corrosion, or loose connections


• Check battery voltage and ground on the CKP circuit to ensure proper power supply


• Use an oscilloscope or a multimeter to test the CKP signal for a clean, consistent waveform at idle and various RPMs


• Inspect the reluctor ring and crankshaft timing components for wear or misalignment


• Verify that other related sensors (e.g., camshaft position sensor) are operating correctly and that their data aligns with CKP readings

After pinpointing the fault, technicians typically test-drive the vehicle to ensure the symptom is reproducible and that the repair resolved the issue.

Repair options and what to expect

Replacement and follow-up steps

Repairing a bad CKP sensor focuses on restoring reliable timing data to the engine control unit. Depending on the root cause, the repair may involve sensor replacement, wiring fixes, or timing-related adjustments.

• Replace the CKP sensor with an OEM or high-quality aftermarket part, ensuring proper orientation, seating, and torque


• Repair or replace damaged wiring or connectors in the CKP circuit; clean and seal connections as needed


• Inspect and replace the reluctor ring or related crank timing components if they are worn or damaged


• In some vehicles, timing adjustments or re-syncing the engine’s timing may be required after sensor replacement


• Clear diagnostic trouble codes and perform a confirmed test drive to verify normal operation and absence of recurring codes

As with any electrical repair, using the correct part, following the vehicle manufacturer’s service manual, and testing the system under real-world conditions are essential to achieving a lasting fix.

Impact on starting and driving

A failing CKP sensor can dramatically affect starting and driving quality. Depending on the fault, you might experience a no-start condition, sudden stalls while driving, or gradual loss of power. In many modern vehicles, the ECM may enter a degraded “limp mode” to protect the engine, allowing limited RPM and speed to get the vehicle to a safe location or shop. Because ignition timing and fuel delivery rely on accurate CKP data, drivability issues often worsen with higher engine load and RPM.

What to do if you suspect a bad CKP sensor

If you notice signs such as intermittent starting issues, stalling, misfires, or illumination of the check engine light with CKP-related codes, schedule a diagnostic with a qualified technician. They will perform a systematic inspection of the sensor, its wiring, and related timing components and confirm the exact cause before replacing parts.

Summary

The crankshaft position sensor is a critical data source for ignition timing and fuel injection. When it goes bad, the engine can fail to start, stall, or run roughly, and you may see warning lights and reduced power. Diagnosis relies on code reading, circuit inspection, and signal testing, while repair typically involves sensor replacement and any needed wiring or timing corrections. With proper diagnosis and timely replacement, most CKP-related drivability problems can be resolved, restoring reliable starting and smooth operation.

What are the symptoms of a bad crank sensor?

Common symptoms of a failing crank sensor include a Check Engine light, hard or no starts, engine stalling or rough idling, misfiring, and poor acceleration. The engine may also vibrate, have reduced gas mileage, or even cause the RPM gauge to act erratically. 
Starting and running issues

• Difficulty starting or no start: The engine may crank but not start, or it may take a long time to start. 
• Engine stalling: The engine can stall while driving, particularly when accelerating. 
• Rough idle: The engine may shake or vibrate noticeably while idling. 

Performance problems

• Engine misfires: The engine may stumble, shake, or run roughly. 
• Poor acceleration: The vehicle may feel sluggish and slow to accelerate. 
• Reduced gas mileage: The engine control module can't optimize fuel injection without accurate timing, leading to lower fuel efficiency. 
• Engine vibrations: You may feel an increase in vibrations, especially during idle or acceleration. 

Other indicators

• Check Engine light: The engine control module will likely trigger the Check Engine light to indicate a fault. 
• Erratic RPM gauge: The tachometer may show sudden spikes or drops in engine speed even at idle. 

Can you drive your car with a bad crankshaft sensor?

No, it is not recommended to drive with a bad crankshaft position sensor because it can lead to stalling, hard starting, poor performance, and potentially leave you stranded. The car may not start at all if the sensor fails completely. 
Risks of driving with a faulty sensor

• Stalling: The engine may stall unexpectedly while you are driving, which is especially dangerous if it happens in traffic. 
• Stalling: The engine may stall unexpectedly while you are driving, which is especially dangerous if it happens in traffic. 
• Engine misfires: You may experience misfires, where the engine hesitates or shakes, which can cause further damage to other components like the catalytic converter if not addressed. 
• Difficulty starting: The car may have a hard time starting, or it may not start at all, leaving you stranded. 
• Poor engine performance: You might notice a decrease in power, poor acceleration, and rough idling. 
• Reduced fuel efficiency: A faulty sensor can send incorrect data to the engine control unit, leading to inefficient fuel usage. 

This video explains how to diagnose a bad crankshaft position sensor: 58sCar Care CluesYouTube · Oct 9, 2024
Recommendation

• The best and safest action is to avoid driving the vehicle and have the sensor diagnosed and replaced as soon as possible. 
• If you must drive a short distance, be prepared for the possibility of the car not starting or breaking down unexpectedly. 

You can watch this video to learn about the symptoms of a bad crankshaft position sensor: 1mEasyAutoFixYouTube · Feb 25, 2023

Can a crankshaft sensor cause engine knock?

No, a bad crankshaft position sensor does not cause knocking; instead, it leads to symptoms like stalling, misfires, and rough idling because the engine computer loses the data it needs for correct timing. However, a bad knock sensor, which is a different part, can allow the engine to make a knocking sound because it cannot detect pre-ignition. Knocking sounds can also result from internal engine problems, such as worn bearings.
 
This video explains the 11 symptoms of a bad crankshaft position sensor: 1mMechanical BoostYouTube · Mar 3, 2024
Symptoms of a bad crankshaft position sensor

• Difficulty starting or the engine won't start at all
• Engine stalling while driving
• Misfires and rough idling
• Rough acceleration or hesitation
• Stalling
• Illuminated "Check Engine" light 

What to do if you hear knocking

• Consult a professional: Knocking is a serious symptom of potential engine damage and should be diagnosed by a mechanic to determine the cause. 
• Check the oil level: Low oil pressure can cause bearing damage and knocking, so ensure your oil level is correct. 
• Use a stethoscope: A mechanic can use a stethoscope or a similar tool to help pinpoint the source of the sound, such as the torque converter or internal engine components. 

This video explains the causes of knocking sound in an engine: 37sHVAC Mechanic YouTube · Apr 4, 2023

What are the 7 symptoms of a bad camshaft position sensor?

Seven common symptoms of a bad camshaft position sensor include the check engine light illuminating, rough idling, engine misfires, poor acceleration, difficulty starting, stalling, and poor fuel economy. A failing sensor can disrupt the engine's timing for fuel injection and ignition, leading to a wide range of performance issues. 
Symptoms of a bad camshaft position sensor

• Check Engine Light: This is often the first and most obvious sign, as the engine control module (ECM) detects an issue with the sensor and triggers the light. 
• Rough Idle: The engine may shake or run unevenly while idling because the sensor is providing incorrect information, leading to inconsistent combustion. 
• Engine Misfires: Inaccurate timing signals can cause the spark plugs to fire at the wrong moment, leading to engine misfires and a rougher-running engine. 
• Poor Acceleration: The vehicle may feel sluggish or hesitate when you press the gas pedal because the ECM is not getting the correct data for optimal air/fuel mixture and spark timing. 
• Difficulty Starting: A faulty sensor can prevent the engine from starting at all, or it may require a longer cranking time before the engine turns over. 
• Engine Stalling: The engine can stall unexpectedly, especially at low speeds or while idling, because the inaccurate signals disrupt the engine's normal operation. 
• Poor Fuel Economy: With incorrect timing, the engine burns fuel less efficiently, which can cause a noticeable drop in your gas mileage.