AutoDiag

P0119

Engine Coolant Temperature Sensor 1 Circuit Intermittent/Erratic

Moderate· Fix soonDIY friendlyPowertrainGeneric, all makes

What it means

The engine coolant temperature (ECT) sensor signal is cutting in and out or jumping around. The engine coolant temperature (ECT) sensor tells the ECU how hot the engine is, which affects fuel mixture, idle speed, cooling fans and the temperature gauge. Intermittent faults are almost always a loose connection, a chafed wire or a sensor that is starting to fail.

Is it safe to drive?

Drivable with care, but you may not get a correct temperature warning. Check the coolant level first and watch for real overheating.

Symptoms

  • Check engine light on
  • Temperature gauge reading wrong or not moving
  • Cooling fans running all the time
  • Hard starting, especially cold
  • Poor fuel economy and black smoke

Probable causes

Most likely first

  1. 1Loose or corroded connector terminals
  2. 2Wiring chafed and shorting intermittently, often where the harness moves with the engine
  3. 3Failing sensor

How to diagnose it

Work through these in order before buying parts

  1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
  2. 2Inspect the engine coolant temperature (ECT) sensor connector and wiring (in the thermostat housing, cylinder head or intake manifold coolant passage). Look for corrosion, bent or pushed-back pins, oil contamination and chafed insulation.
  3. 3Watch the engine coolant temperature (ECT) sensor reading on live data. After a cold soak it should match the outside temperature. With the engine warm it should rise steadily to about 85–105 °C (185–220 °F) and stay there.
  4. 4Unplug the sensor and measure its resistance; it should drop smoothly as it warms up (compare with the chart in a service manual). With the key on, the ECU side of the connector should show about 5 volts on the signal wire and a good ground on the other.
  5. 5Wiggle the harness and connector while watching live data. A jump in the reading pinpoints the bad spot.
  6. 6Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

  • Repair the damaged wiring or connector
  • Replace the engine coolant temperature (ECT) sensor
  • Clear the code and test drive to confirm the repair

This information is general guidance for all makes. Exact causes, specifications and procedures vary by vehicle, so confirm with your service manual or a qualified mechanic before replacing parts.