Advertiser Disclosure

What’s Wrong With My Car? Diagnosing Common Problems

You’ll likely need to see a mechanic, but how your car smells, feels or sounds can offer warning signs for common car problems.
April 30, 2018
Auto Loans
NerdWallet adheres to strict standards of editorial integrity to help you make decisions with confidence. Some of the products we feature are from partners. Here’s how we make money.
We adhere to strict standards of editorial integrity. Some of the products we feature are from our partners. Here’s how we make money.

If your car is vibrating, making noises or emitting odors, you’ll probably be seeing a mechanic soon. But before you do, a few minutes of troubleshooting on your own will help you talk to your mechanic and budget for the repair cost.

We have suggestions for how to proceed if:

» SIGN UPSee your car’s value and manage expenses

Your car smells like gas

It could be a faulty gas cap or a more serious problem with the fuel system.

Sometimes a gas smell isn’t a harbinger of costly repairs. Assuming the odor isn’t simply from your last stop at the gas station, it could be a loose or broken gas cap. A common culprit, gas caps are cheap to replace.

If the odor persists and it isn’t a faulty gas cap, it could be a more serious, and potentially dangerous, problem with your fuel system, like:

  • Fuel tank leak, often accompanied by a rainbow puddle under your car
  • Fuel injector, line or filter leak
  • A faulty component of your car’s evaporative emissions (EVAP) system, often accompanied by a check engine light
Connected to fuel lines and tanks, the EVAP system has many components and prevents emissions from escaping the engine. When one part fails, a gasoline smell can seep out. Worn or failing EVAP parts are one of the most common causes of check engine light repairs, according to CarMD, which found that various EVAP-related repairs, including parts and labor, each cost less than $300 on average in 2016.

Your car shakes, pulsates or vibrates

After your car gets some miles on it, you notice a little shake or rough idle here and there. Possible explanations include:

  • Worn spark plugs and wires, possibly with check engine light
  • Loose or disconnected hoses around the engine
  • Loose battery terminal connections
  • Loose timing belt
  • Wheels out of balance
  • Worn brake rotors
  • Worn shocks or struts
This is a relatively low-cost fix. Replacing these items cost an average of $342, including parts and labor, in 2016, according to CarMD. Conventional spark plugs last 12,000 to 25,000 miles, but manufacturers of long-life spark plugs say they can last beyond 100,000 miles.

Other signs you may need new spark plugs and wires: decreased fuel efficiency, reduced acceleration, engine misfiring or car not starting.

Your car is emitting white smoke

A little white vapor coming from your tailpipe that disappears quickly is likely just normal condensation evaporating.

Persistent white smoke is likely due to a coolant leak, a serious issue.

But white smoke coming from the tailpipe that doesn’t dissipate quickly typically means coolant is leaking and burning when it enters the combustion chamber in the engine.

This can be a pretty serious issue, so be sure to find an experienced mechanic. Possible problems range in severity and include:

  • A blown head gasket
  • Damaged cylinder head
  • Cracked engine block

Repairs will likely set you back at least $1,000 — and much more if your engine must be rebuilt or replaced.

Smoke (or steam) coming from the engine or under the hood is probably the result of coolant leaking from its reservoir and reacting with the heat of the engine. Other telltale signs of a coolant leak: a sweet or syrupy odor and overheating.

Possible problems (which will likely need professional fixing) include:

  • A bad thermostat
  • Using the wrong coolant. Always check your car’s manual before adding fluids.
  • A worn or damaged radiator or related part
  • A bad water pump or hose

Your car smells like sulfur or rotten eggs

Unless you left last week’s leftovers in your car, this smell is probably an indication that you need your catalytic converter replaced, a common and expensive repair.

It’s a relatively common problem, and probably quick to fix, meaning labor could be pretty cheap. But that doesn’t go for the part itself — expect to pay $900 to $2,500, according to RepairPal.

Other possible reasons your car smells like rotten eggs include:

  • Faulty fuel pressure regulator or filter. Replace your fuel filter.
  • Low-quality fuel. Try upgrading to Top-Tier gas and make sure you’re choosing the octane level your owner’s manual suggests.

Your car makes noise when you turn

Various noises signal issues with the steering and suspension systems.

Normal wear and tear can take its toll on your car’s steering and suspension systems, which can complain loudly when it happens. Warning signs can take the form of:

  • Creaking or squealing upon turning, which could be from worn or damaged parts, joints that need greasing or from low power-steering fluid
  • Clicking when you turn, likely a problem with a constant-velocity (CV) joint or boot
  • A clunking noise when you drive, even when you aren’t turning
  • Difficulty turning the steering wheel. Check your power steering fluid.
This is typically a problem with one of your car’s belts, such as the timing belt or drive belt. But it could also be a problem with a pulley or tensioner that keeps your belts running. Depending on your car, you can check the belts and call a mechanic if they look:

  • Dry or cracked
  • Loose
  • Frayed or ripping at edges

Your car won’t start

Your non-starter probably falls into one of two categories: The engine cranks when you turn the key, or it’s silent or makes a quiet clicking noise. You can narrow down the problem by its sound (or lack thereof) when you turn the key.

  • Out of gas
  • Fuel pump failure
  • Worn-out spark plugs
  • Faulty security system
  • Frozen fuel line — less common

  • Dead battery
  • Bad alternator
  • Worn starter
  • Wheel lock. If the key doesn’t turn at all, try moving or adjusting the steering wheel.

About the author