Troubleshooting Your 1999 Jeep Cherokee Crank Sensor

My 1999 Jeep Cherokee refused to start the other day, leaving me stranded. After some frantic Googling, I discovered it might be the crank sensor. This experience taught me a valuable lesson about car maintenance, and in this post, I’ll share everything I learned about diagnosing and replacing a faulty crank sensor in a 1999 Jeep Cherokee. You’ll learn how to identify the symptoms, locate the sensor, and complete the replacement process, saving you time and money on potential mechanic fees.

Identifying a Faulty Crank Sensor

This section will cover the common signs of a failing crank sensor in your 1999 Jeep Cherokee. We’ll explain how these symptoms manifest and what causes them, allowing you to diagnose the problem accurately before you start replacing parts.

Symptoms of a Bad Crank Sensor

• Engine Cranking but Not Starting: This is a classic symptom. The engine turns over, but it doesn’t fire up. The crank sensor’s failure to send the signal to the computer prevents the ignition system from starting. This issue typically won’t produce any error codes, but the crank sensor is an excellent starting point when diagnosing starting problems.
• Intermittent Starting Problems: Sometimes the Jeep starts without issues, but other times, it refuses to turn over. This intermittent nature suggests a problem with a component that can function erratically under specific conditions, and a faulty crank sensor is a prime suspect.
• Rough Idle: An erratic or rough engine idle can indicate several issues, but a malfunctioning crank sensor can negatively affect the engine’s timing and fuel delivery, leading to a rough idle.
• Check Engine Light (with relevant codes): While not always the case, a malfunctioning crank sensor may trigger a check engine light. Obtain a diagnostic code reading to see if the codes point towards a crank sensor issue. Codes P0335, P0336, P0337, P0338, or similar variations typically relate to crankshaft sensor circuit malfunctions.

Causes of Crank Sensor Failure

• Wear and Tear: Over time, the sensor’s internal components can wear down, leading to inaccurate readings or complete failure. This wear happens due to constant vibration and exposure to engine heat.
• Physical Damage: The crank sensor is relatively exposed and vulnerable to physical damage from impacts or debris. A collision or a dropped tool could cause the sensor to fail.
• Wiring Issues: Damage to the sensor’s wiring harness, such as shorts, corrosion, or loose connections, can affect its functionality and lead to intermittent problems. Check the wiring carefully for breaks or fraying.
• Oil Leaks: Excessive oil leaking onto the sensor can cause it to malfunction. Oil can compromise the sensor’s electrical connections and result in erratic readings.

Locating the Crank Sensor on a 1999 Jeep Cherokee

Knowing the exact location of the crank sensor in your 1999 Jeep Cherokee is crucial for efficient replacement. We will guide you through identifying its position, highlighting potential challenges you might encounter during the process.

Identifying the Crank Sensor

The crank sensor on a 1999 Jeep Cherokee is typically located near the bottom of the engine, close to the crankshaft. Consult your Jeep Cherokee repair manual or online resources (with images) to confirm the exact location specific to your engine type. It’s a small cylindrical sensor with a single wire harness connecting it to the engine control module (ECM).

Accessing the Crank Sensor

1. Prepare Your Jeep: Ensure the Jeep is safely parked on a level surface, and the engine is cool. Disconnect the negative battery terminal to prevent electrical shorts.
2. Access the Sensor: Depending on your engine type, you may need to remove some components like an engine cover or part of the undercarriage to access the crank sensor. Some space and tools may be needed. Consult a repair manual for specific instructions for your engine.
3. Visual Inspection: Once the sensor is visible, carefully inspect it for any signs of damage, such as cracks, corrosion, or oil leakage. Note that the sensor is usually close to the bottom of the engine near the oil pan.

Replacing the Crank Sensor

This section details the step-by-step process of replacing the faulty crank sensor, offering practical advice and safety precautions. We will cover the tools you’ll need, the replacement procedure itself, and how to verify that the new sensor functions correctly after installation.

Tools and Materials

• New Crank Sensor: Ensure you purchase a replacement crank sensor that is specifically compatible with your 1999 Jeep Cherokee’s engine. Always double-check the part number against your vehicle’s specifications.
• Socket Wrench Set: You will likely need various socket sizes to remove and install the crank sensor and other components that might need to be removed to access it.
• Ratchet and Extensions: A ratchet and extensions will be necessary to reach the crank sensor, especially in tight engine bay areas.
• Torque Wrench: To ensure the new sensor is correctly tightened and avoid damaging the engine components.
• Wrench for the Battery Terminal: To safely disconnect and reconnect the battery. Avoid short circuits.

Replacement Procedure

1. Disconnect the Old Sensor: Carefully unplug the electrical connector from the old sensor. Note the orientation or make a picture to help with reinstallation. Take a picture of the wiring to ensure that the new sensor is wired correctly.
2. Remove the Old Sensor: Use the appropriate socket wrench to carefully remove the sensor from its mounting location. Be gentle to avoid damaging the threads.
3. Install the New Sensor: Carefully install the new crank sensor into its mounting location. Hand-tighten it first, then use the torque wrench to tighten it to the manufacturer’s specified torque setting. Using the wrong torque can damage the sensor or its mounting point.
4. Reconnect the Connector: Carefully plug the electrical connector into the new crank sensor, ensuring a secure connection. Ensure that the connector snaps into place firmly and securely.
5. Reconnect the Battery: Reconnect the negative battery terminal.
6. Test the Jeep: Start the Jeep and check for any improvements in starting or running. If the issue persists, double-check your work or consult a mechanic.

Verifying the Sensor

After installing the new crank sensor, start the Jeep to see if the problem is resolved. If it starts normally, it’s likely you have successfully fixed the issue. If the problem persists, check for any additional problems in the electrical system, or seek a mechanic for more advanced diagnosis.

Understanding Crank Sensor Function

This section delves into the technical aspects of the crank sensor’s role in your Jeep’s engine. It will explain how the sensor works, the data it provides to the computer, and the importance of its accurate functioning for optimal engine performance.

How the Crank Sensor Works

The crank sensor is a crucial component of your Jeep Cherokee’s ignition system. It’s a type of magnetic sensor that detects the rotation of the crankshaft, providing the engine control module (ECM) with data on the engine’s speed and position. This information allows the ECM to accurately time the ignition and fuel injection, ensuring optimal engine performance.

Crank Sensor Signal to the Engine Control Module

The crank sensor doesn’t just tell the ECM how fast the crankshaft is turning; it also provides positional information. This is crucial for determining the precise moment to ignite the fuel-air mixture for each cylinder. If the timing is off, even slightly, you can expect rough engine performance. An incorrect signal will result in misfires and a complete failure to start. The sensor generates a signal based on the crankshaft’s position, which is precisely measured using a magnetic field.

Importance of Accurate Crank Sensor Data

• Precise Fuel Injection Timing: The crank sensor helps deliver the correct amount of fuel at precisely the right moment. Without it, the fuel delivery would be inaccurate, causing the engine to run poorly, possibly damaging the catalytic converter.
• Optimal Ignition Timing: The precise timing of the spark plug ignition is critical for efficient combustion. Inaccurate sensor data could lead to misfires, poor engine performance, and even engine damage.
• Anti-Theft System Integration: In some vehicles (not confirmed on all 1999 Jeep Cherokees), the crank sensor plays a role in the anti-theft system, making sure that the vehicle can start only under specific conditions, adding a layer of security.

Common Myths and Misconceptions

This section will address some common misconceptions surrounding crank sensor issues and their diagnoses. We will debunk these myths and provide accurate information to help prevent misdiagnosis and unnecessary repairs.

Myth 1: A Bad Crank Sensor Always Throws a Code

While a failing crank sensor often triggers a check engine light with a diagnostic trouble code (DTC), it’s not always the case. Sometimes, the sensor’s failure is intermittent, not causing the car to continuously throw a code. A proper diagnostic is still needed to rule out other potential causes.

Myth 2: Replacing the Crank Sensor is Extremely Difficult

Replacing the crank sensor can seem daunting, but for many vehicles, including most 1999 Jeep Cherokees, it is a relatively straightforward repair that even moderately experienced DIY mechanics can tackle. Access to the sensor might vary by engine type, but the general procedure is usually manageable.

Myth 3: A Crank Sensor is Expensive to Replace

A crank sensor is relatively inexpensive compared to other engine components. The cost of the sensor itself is usually much lower than the labor cost of having a mechanic replace it. Replacing it yourself can save a significant amount of money.

FAQ

What are the most common causes of crank sensor failure in a 1999 Jeep Cherokee?

The most common causes are normal wear and tear from engine heat and vibrations, physical damage from impacts, and wiring issues like corrosion or shorts. Oil leaks onto the sensor can also lead to failure.

How much does it cost to replace a crank sensor in a 1999 Jeep Cherokee?

The cost of the sensor itself is relatively low, usually under $50. However, labor costs can vary depending on whether you do it yourself or have a mechanic do it. Labor costs can range from $50 to $150 or more depending on your location.

Can I drive my Jeep Cherokee if the crank sensor is bad?

It’s not recommended. While you might be able to get it started sometimes, driving with a bad crank sensor can lead to other issues like misfires and poor engine performance. It might also cause the engine to not start altogether when you most need it.

How long does it take to replace a crank sensor?

The replacement time varies depending on vehicle access and your mechanical aptitude. It can take anywhere from 30 minutes to a couple of hours. Refer to a repair manual for specific information related to your engine type.

What are the long-term effects of driving with a faulty crank sensor?

Continued driving with a bad crank sensor can lead to engine damage from misfires and poor fuel mixture. It can also damage your catalytic converter. It is best to have this repaired as soon as the sensor fails to function correctly.

Are there any special tools required to replace a crank sensor?

Typically, you will need basic hand tools, including sockets, a ratchet, and possibly extensions to reach the sensor. A torque wrench is highly recommended to ensure the sensor is properly tightened.

Final Thoughts

Dealing with a faulty crank sensor in your 1999 Jeep Cherokee can be frustrating, but understanding the symptoms, location, and replacement process empowers you to handle the situation effectively. By following the steps outlined in this guide, you can potentially save on expensive repair bills while gaining valuable hands-on automotive experience. Remember to always consult your vehicle’s repair manual for specific instructions and safety precautions. If you’re unsure about any aspect of the repair, it’s always best to seek professional help.