If your check engine light is on and a scan shows code P0118, you’re dealing with a high input signal from the engine coolant temperature sensor. That sounds technical, but what it really means is your car’s computer thinks the coolant is way colder than it actually is sometimes reading below -40°F. This isn’t just a glitch. It can mess with fuel delivery, idle quality, and even cause overheating if ignored.

How much does it cost to fix a P0118 code?

Most drivers pay between $150 and $350 total. The sensor itself usually costs $20 to $80, depending on your vehicle. Labor runs $100 to $250 because replacing it often takes less than an hour, though some engines tuck the sensor in awkward spots. If the wiring or connector is damaged, add another $50 to $150 for diagnosis and repair.

Keep in mind: if you’ve been driving with this code for a while, you might have secondary damage. A faulty reading can cause the engine to run rich (too much fuel), which wears out spark plugs or fouls the catalytic converter. Those repairs cost hundreds more, so don’t wait.

What actually causes the P0118 code?

The most common culprit is a failed coolant temperature sensor. But it’s not always that simple. Sometimes the wiring harness has a short or open circuit, especially near hot engine parts or sharp brackets. Corrosion in the connector, low coolant level, or even a bad ground connection can also trigger it.

You can read more about what causes the high input signal if you’re curious why the sensor reads abnormally cold. Spoiler: it’s usually not magic just physics and wear.

Can I drive with a P0118 code?

Technically, yes but not wisely. Your engine may idle rough, hesitate during acceleration, or burn extra fuel. In winter, you might notice poor cabin heat. Worse, if the sensor fails completely or the problem masks real overheating, you risk warping the cylinder head or blowing a head gasket.

If you see steam, smell coolant, or the temperature gauge climbs into the red, pull over immediately. Learn how a faulty sensor can lead to engine overheating, even if the gauge looks normal.

Should I replace it myself?

If you’re comfortable with basic tools and your car’s layout, yes. The sensor screws into the engine block or thermostat housing and unplugs easily. Just make sure the engine is cool, drain some coolant first (to avoid spills), and use a little thread sealant when reinstalling.

Mistakes people make: forcing the connector, not checking coolant level afterward, or assuming the new sensor will fix everything without clearing the code. Always reset the ECU after replacement.

When to call a mechanic

If you’ve replaced the sensor and the code comes back, the issue is likely in the wiring or the ECU itself. That’s when professional diagnosis matters. A good shop will test voltage at the sensor plug and trace the circuit back to the computer. You can learn what that process looks like in this piece on how mechanics diagnose high voltage issues.

Also call a pro if you’re unsure where the sensor is, don’t have OBD2 tools to clear codes, or notice coolant leaks around the replacement area.

Quick checklist before you spend money

  • Check your coolant level low fluid can cause false readings.
  • Inspect the sensor’s wiring for burns, frays, or rodent damage.
  • Clear the code and see if it returns immediately intermittent codes need deeper digging.
  • Compare aftermarket sensor prices OEM isn’t always better, but ultra-cheap ones often fail fast.
  • Ask for a diagnostic fee waiver if you book the repair at the same shop.

Start by scanning the code again to confirm it’s still P0118. Then check your coolant level and look under the hood for obvious wiring issues. If all looks fine, replacing the sensor is a reasonable first step and often the only one needed.