P0118 Engine Coolant Temperature Sensor High: Fix Guide

P0118 Engine Coolant Temperature Sensor High

This guide covers everything you need to know about P0118 code fix. We've researched the most common causes, real diagnostic procedures, and actual repair costs. This is one of the most searched automotive repair topics (25K+/month), so we've made it comprehensive.

Symptoms

  • Check engine light
  • Temperature gauge reads cold or max
  • Poor fuel economy
  • Hard starting when warm
  • Cooling fans running constantly

Common Causes (Ranked by Likelihood)

Cause Likelihood Repair Cost DIY?
Failed ECT sensor 60% $20-150 ✅ Yes
Corroded connector or wiring 25% $10-100 ✅ Yes
Low coolant level 10% $10-30 ✅ Yes
Faulty PCM 5% $500-1500 ❌ No (shop needed)

Tools You'll Need

  • OBD-II scanner
  • Multimeter
  • Replacement ECT sensor
  • Coolant

Step-by-Step Diagnosis

  1. Check coolant level - top up if low
  2. Locate ECT sensor (usually near thermostat housing)
  3. Disconnect connector - check for coolant intrusion or corrosion
  4. Measure sensor resistance - compare to spec chart (changes with temp)
  5. At 68°F (20°C), most sensors read 2000-3000 ohms
  6. At 176°F (80°C), most sensors read 300-400 ohms
  7. Check for 5V reference voltage at connector with key on

Pro Tips

  • A stuck-open thermostat can cause erratic ECT readings
  • Some vehicles have two ECT sensors - one for PCM, one for gauge
  • Always replace the coolant if the sensor is removed

Service Manuals for Your Vehicle

Every repair is easier with the factory service manual. Here are the manuals we carry for vehicles commonly affected by this issue:

Toyota Corolla

Honda Accord

Ford Focus

Nissan Maxima

Chevrolet Malibu

When to Get the Full Service Manual

This guide covers the general process, but every vehicle is different. Torque specs, wiring diagrams, and procedures specific to your year and model are in the factory service manual. For $49, you get the exact procedures the dealership mechanics use—including torque specs, fluid capacities, wiring diagrams, and diagnostic flowcharts.

Browse all service manuals →

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