P0117 medium Severity

P0117: Engine Coolant Temperature (ECT) Sensor Circuit Low Input

May cause erratic idle, poor fuel economy, hard starting, and potential engine overheating due to incorrect coolant temperature data.

Overview

P0117 indicates a low voltage or low input condition detected in the Engine Coolant Temperature (ECT) sensor circuit, meaning the PCM receiving an abnormally low signal from the coolant temperature sensor, often implying electrical issues or sensor failure.

Common Symptoms

  • Illuminated Check Engine Light
  • Poor fuel economy
  • Rough idle or poor drivability
  • Difficulty starting engine
  • Engine overheating or abnormal temperature readings

Most Common Causes

Faulty engine coolant temperature (ECT) sensor high

Sensor may be internally shorted or degraded causing low voltage return signal.

Short to ground or open in ECT sensor wiring high

Wiring harness damage, chafing, or shorting can pull voltage lower than expected.

Poor or corroded sensor connector or terminals medium

Corrosion at connectors increases resistance and lowers signal voltage.

Low coolant level or air pockets medium

Inaccurate sensor readings due to improper coolant contact with the ECT sensor.

Faulty PCM/ECM low

Rare but possible if reference voltage output or interpretation is incorrect.

Diagnostic Steps

  1. Retrieve freeze frame data and verify P0117 presence with OBD-II scanner.
    Expected: Code P0117 present; no other sensor faults interfering.
    Interpretation: Code confirms an issue with ECT circuit low input.
  2. Visually inspect ECT sensor wiring and connectors for damage or corrosion.
    Expected: No broken wires, chafing, or loose/corroded connectors.
    Interpretation: Damaged wiring/connectors likely cause if issues found.
  3. Measure sensor signal voltage with engine cold and warm using scan tool.
    Expected: Voltage should be within normal reference range (approx 0.5–4.5V).
    Interpretation: Low reading confirms low input condition; proceed to isolate wiring or sensor.
  4. Unplug ECT sensor and observe voltage change on scan tool live data.
    Expected: Voltage should jump to an extreme cold reading if sensor is shorted.
    Interpretation: No change suggests wiring or PCM issues.
  5. Check PCM reference 5V supply and ground for ECT circuit.
    Expected: Stable 5V reference and good ground.
    Interpretation: Lack of reference voltage indicates PCM or shared circuit problem.

Repair Solutions

Replace faulty ECT sensor easy
Estimated Cost: $30 - $150

Most common fix; confirm wiring and connectors are good prior to replacement.

Repair or replace damaged ECT sensor wiring/harness medium
Estimated Cost: $50 - $250

Includes repairing chafed wires and replacing corroded connectors.

Flush, bleed cooling system and top up coolant medium
Estimated Cost: $50 - $120

Ensures correct sensor contact with coolant; may reveal air pockets causing misreadings.

PCM/ECM diagnostic and potential replacement hard
Estimated Cost: $200 - $1000

Rare; only after exhaustive wiring/sensor evaluation and confirmation of module fault.

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Replacing the ECT sensor without checking wiring, connectors, or coolant condition
  • Assuming thermostat failure when the issue is electrical
  • Interpreting false high temperature as overheating instead of a sensor circuit fault

Frequently Asked Questions

What does a P0117 diagnostic trouble code signify?

When your OBD-II scanner reads P0117, it means: Engine Coolant Temperature (ECT) Sensor Circuit Low Input. This code is related to the vehicle's Sensors.

Should I stop driving if I have P0117?

You should treat P0117 as a medium issue. May cause erratic idle, poor fuel economy, hard starting, and potential engine overheating due to incorrect coolant temperature data.

What are the symptoms of P0117?

Common symptoms include: Illuminated Check Engine Light, Poor fuel economy, Rough idle or poor drivability. You might also notice the Check Engine Light is on.

What parts fail when P0117 is set?

The most common causes are: Faulty engine coolant temperature (ECT) sensor, Short to ground or open in ECT sensor wiring, Poor or corroded sensor connector or terminals.

Is P0117 expensive to fix?

Expect to pay around $120 if the issue is a Flush, bleed cooling system and top up coolant, but up to $1000 if the PCM/ECM diagnostic and potential replacement needs replacement.

Is the P0117 code specific to Honda?

P0117 is not specific to any one brand. It can appear on Ford, Dodge, Toyota, Honda, Jeep, and other vehicles.

User Comments (0)

Share your experience or ask a question about this code.

Be the first to share your experience with P0117!