Why is My Car Jerking? How to diagnose by yourself?

Driving a car that jerks unexpectedly can be both frustrating and concerning. Jerking, or sudden, uneven movements while driving, is often a sign that something is wrong with your vehicle. This issue can occur during acceleration, deceleration, or even while maintaining a constant speed. Understanding the potential causes of this problem can help you diagnose and address it before it leads to more serious damage or safety hazards. In this article, we’ll explore the most common reasons why your car might be jerking and what you can do to fix it.

Possible Reasons Your Car Jerks

1. Fuel System Issues

One of the most common causes of car jerking is a problem with the fuel system. If your car isn’t receiving a consistent supply of fuel, it can lead to uneven engine performance. Here are some specific fuel-related issues to consider:

• Clogged Fuel Filter: Over time, the fuel filter can become clogged with dirt and debris, restricting the flow of fuel to the engine. This can cause the engine to sputter and jerk, especially during acceleration.
• Fuel Pump Failure: The fuel pump is responsible for delivering fuel from the tank to the engine. If the pump is failing, it may not provide a steady stream of fuel, leading to jerking or stalling.
• Dirty Fuel Injectors: Fuel injectors spray fuel into the engine’s combustion chambers. If they become clogged or dirty, they may not deliver fuel evenly, causing the engine to jerk.

Solution: Regularly replace your fuel filter as recommended by your vehicle’s manufacturer. If you suspect a fuel pump or injector issue, have a mechanic inspect and clean or replace the affected components.

2. Ignition System Problems

The ignition system is responsible for creating the spark that ignites the fuel in the engine. If any part of this system fails, it can lead to misfires, which often cause jerking. Common ignition system issues include:

• Faulty Spark Plugs: Worn or damaged spark plugs can cause inconsistent sparks, leading to engine misfires and jerking.
• Bad Ignition Coils: Ignition coils amplify the voltage needed to create a spark. If a coil fails, it can cause one or more cylinders to misfire.
• Damaged Spark Plug Wires: Cracked or worn spark plug wires can interfere with the electrical current, leading to weak or inconsistent sparks.

Solution: Inspect and replace spark plugs and wires as needed. If the problem persists, have a mechanic check the ignition coils and other ignition system components.

3. Transmission Troubles

If your car jerks while shifting gears or during acceleration, the transmission could be the culprit. Transmission issues can be particularly serious and expensive to repair, so it’s important to address them early. Potential transmission-related causes include:

• Low Transmission Fluid: Transmission fluid lubricates and cools the transmission. If the fluid level is low, it can cause the transmission to jerk or hesitate during gear changes.
• Worn Clutch (Manual Transmission): In manual vehicles, a worn clutch can cause jerking, especially when engaging or disengaging gears.
• Faulty Torque Converter (Automatic Transmission): The torque converter transfers power from the engine to the transmission. If it fails, it can cause jerking or shuddering.

Solution: Check the transmission fluid level and top it up if necessary. If you suspect a more serious issue, such as a worn clutch or faulty torque converter, consult a professional mechanic.

4. Airflow and Sensor Issues

Modern cars rely on a variety of sensors to regulate engine performance. If any of these sensors fail or become dirty, it can disrupt the air-fuel mixture, leading to jerking. Common sensor-related issues include:

• Dirty Mass Airflow Sensor (MAF): The MAF sensor measures the amount of air entering the engine. If it becomes dirty or fails, it can send incorrect data to the engine control unit (ECU), causing jerking or hesitation.
• Faulty Oxygen Sensor: The oxygen sensor monitors the amount of oxygen in the exhaust gases. A faulty sensor can cause the engine to run too rich or too lean, leading to jerking.
• Throttle Position Sensor (TPS) Issues: The TPS monitors the position of the throttle and sends this information to the ECU. If it fails, it can cause erratic acceleration and jerking.

Solution: Clean or replace the MAF sensor and oxygen sensor as needed. If the TPS is faulty, it may need to be replaced by a professional.

5. Exhaust System Blockages

A blocked exhaust system can restrict the flow of exhaust gases, causing backpressure that affects engine performance. This can lead to jerking, especially during acceleration. Common causes include:

• Clogged Catalytic Converter: The catalytic converter reduces harmful emissions, but it can become clogged over time. A clogged converter can cause jerking, reduced power, and even engine stalling.
• Damaged Exhaust Pipes: Dents or blockages in the exhaust pipes can also restrict airflow, leading to jerking.

Solution: Have a mechanic inspect the exhaust system for blockages or damage. If the catalytic converter is clogged, it may need to be replaced.

6. Electrical Problems

Electrical issues can also cause your car to jerk. These problems can be tricky to diagnose, as they often involve intermittent faults. Potential electrical issues include:

• Faulty Wiring: Damaged or corroded wiring can interfere with the electrical signals needed for proper engine operation.
• Weak Battery: A weak or failing battery can cause voltage fluctuations, leading to jerking or stalling.
• Alternator Issues: The alternator charges the battery and powers the electrical system. If it fails, it can cause inconsistent engine performance.

Solution: Have a mechanic inspect the electrical system, including the battery, alternator, and wiring, to identify and fix any issues.

How to Diagnose Car Jerking Problems Using XTOOL D7S Diagnostic Scanner

Using a car diagnostic (OBD-II scanner) can help you quickly identify problems with your vehicle, including what is causing it to shake. Below are the detailed steps to diagnose the above problems using a diagnostic instrument:

1. Preparation

Obtain a diagnostic device: Purchase or borrow an OBD-II scanner. Most modern cars (manufactured after 1996) are equipped with an OBD-II interface.

Locate the OBD-II port: usually located under the driver's side dashboard, near the steering wheel. If you can't find it, refer to your vehicle owner's manual.

Turn off the engine: Make sure the vehicle is turned off before connecting the diagnostics.

2. Connecting the Diagnostic Device

Plug the OBD-II scanner into the vehicle's OBD-II port.

Turn on the vehicle power (no need to start the engine) and the diagnostic will start automatically.

Wait for the diagnostic instrument to establish a connection with the vehicle's Electronic Control Unit (ECU).

3. Reading Error Codes (DTCs)

Select “AUTO SCAN”.

The diagnostic scanner will scan the vehicle's ECU and display the trouble codes (usually a combination of letters and numbers, e.g. P0300).

Make a note of all the fault codes, which can help you determine the source of the problem.

4. Interpreting fault codes

Use the diagnostic instrument's owner's manual or an online resource (such as the OBD-II trouble code database) to decipher the trouble codes. Here are some common trouble codes and their possible causes:

P0171/P0174: the Fuel system is too thin (could be a fuel pump, injector or air flow sensor problem).

P0300: Random/multi-cylinder misfire (could be a spark plug, ignition coil, or fuel system problem).

P0420: Catalytic converter inefficiency (could be a clogged catalytic converter or faulty oxygen sensor).

P0700: Transmission control system malfunction (could be transmission sensor or fluid level problem).

P0101: Air flow sensor performance problem (could be a dirty or damaged sensor).

If you are unfamiliar with diagnosis and repair, it is recommended that you take your vehicle to a professional mechanic. Some problems may require more specialized equipment (such as an oscilloscope) to diagnose. When removing or replacing parts, always refer to your vehicle's service manual to ensure proper operation.

By following these steps, you can effectively use your automotive diagnostic to find and solve the problem that is causing your car to shake. If the problem is complicated or cannot be solved, contact a repair professional promptly.