P0118 on a 2017 Hyundai Elantra
Coolant Temp Sensor High Input
P0118 on a 2017 Hyundai Elantra indicates coolant temp sensor high input. It usually stays drivable short-term but should be diagnosed promptly. The most common cause is disconnected or unlatched ect sensor connector (typically $0–$50). Confirm the root cause before replacing parts.
What does P0118 mean on a 2017 Hyundai Elantra?
P0118 is set when the engine control module reads the engine coolant temperature sensor signal voltage above the calibrated maximum — typically a reading that would represent an unrealistically cold coolant temperature (often −40 °F / −40 °C). This is the open-circuit fingerprint for the ECT sensor: a disconnected sensor, a broken signal wire, or a sensor failed open internally.
This guide covers P0118 across the 2015-2019 Hyundai Elantra generation — the symptoms, causes, and diagnostic steps below apply to every model year from 2015 through 2019.
Is it safe to drive a 2017 Hyundai Elantra with P0118?
In most cases a 2017 Hyundai Elantra stays drivable for short trips with P0118 active, but diagnose and repair it promptly. This is a moderate-severity code — ignoring it can lead to further damage or a failed emissions test.
What are the symptoms of P0118 on a 2017 Hyundai Elantra?
- Check Engine Light is illuminated
- Temperature gauge reads zero or stays cold
- Difficult cold start with rich-running symptoms
- Cooling fans may run constantly (ECM thinks coolant is dangerously cold)
- Slightly reduced fuel economy
- Cold-running engine doesn't warm up properly per the gauge
- Possible hard start when the engine is hot (ECM commands cold-start enrichment)
What causes P0118 on a 2017 Hyundai Elantra?
| Cause | Likelihood | Estimated repair (USD) |
|---|---|---|
| Disconnected or unlatched ECT sensor connector | Most common | $0–$50 |
| Broken or chafed ECT signal wire (open circuit) | Common | $80–$350 |
| Internally failed ECT sensor (element opened) | Common | $30–$200 |
| Corroded sensor connector pins | Common | $30–$200 |
| Damaged sensor body from coolant leak or freeze | Occasional | $50–$250 |
| Failed PCM signal input (rare) | Rare | $400–$1,500 |
How to diagnose this on a 2017 Hyundai Elantra
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Read ECT temperature with a scan tool
A working ECT reads close to ambient air temperature when the engine has been off long enough to cool. A reading of "−40 °F" or "−40 °C" is the classic open-circuit fingerprint.
Tools: Scan tool with ECT PID
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Inspect the connector and visible wiring
Locate the ECT sensor (usually threaded into the intake manifold or thermostat housing). Unplug, inspect for corrosion, water, bent pins. Re-seat and clear the code — if it stays clear, the connector was the problem.
Tools: Electrical contact cleaner, Flashlight
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Bench-test the ECT sensor resistance
Remove the sensor (place a rag — coolant will drip). Measure resistance across its terminals at room temperature. Compare to the service manual — most NTC ECTs read 2.0–4.5 kΩ at 68 °F (20 °C). Infinite resistance means the sensor is open and needs replacement.
Tools: Multimeter, Service spec sheet, Coolant catch and replacement
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Verify signal-wire continuity to the PCM
With the ECT disconnected, check continuity from the sensor's signal wire to the corresponding PCM pin. Open circuit confirms a broken wire somewhere along the path. Visual inspection of the harness — particularly where it routes near hot exhaust or moving accessories — often reveals the chafe point.
Tools: Multimeter, Wiring diagram
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Jumper-test the signal wire
With the ECT disconnected, briefly jumper the signal wire to ground and observe the scan tool — the reading should swing from "very cold" to "very hot." No swing points at the wiring or PCM input rather than the sensor.
Tools: Jumper wire, Scan tool
NHTSA complaints & recalls for the 2017 Hyundai Elantra
Owner-reported safety complaints and official recalls filed with the U.S. National Highway Traffic Safety Administration for the 2017 Hyundai Elantra. Use these to gauge how common a problem is on your specific vehicle before you start chasing Hyundai Elantra diagnostics.
- ENGINE 283
- POWER TRAIN 60
- STRUCTURE 131
- UNKNOWN OR OTHER 129
- ELECTRICAL SYSTEM 110
4 active recalls
- STEERING:ELECTRIC POWER ASSIST SYSTEM Mar 2017
Hyundai Motor America (Hyundai) is recalling certain 2017 Elantra vehicles. The affected vehicles may have a damaged Electronic Power Steering (MDPS) connector resulting in a loss of electric power steering assistance.…
NHTSA campaign 17V213000 - AIR BAGS:FRONTAL:DRIVER SIDE:INFLATOR MODULE Dec 2016
Hyundai Motor Company (Hyundai) is recalling certain model year 2017 Hyundai Elantra vehicles manufactured April 15, 2016, to September 13, 2016, and Sonata vehicles manufactured May 27, 2016 to September 16, 2016. In these vehicles, the end seal for the driver's frontal air bag…
NHTSA campaign 16V956000 - SERVICE BRAKES, HYDRAULIC:POWER ASSIST:HYDRAULIC Jan 2017
Hyundai Motor Company (Hyundai) is recalling certain 2017 Elantra vehicles. In the affected vehicles, the brake booster may fail, resulting in a loss of power brake assist.…
NHTSA campaign 17V063000 - AIR BAGS:FRONTAL Apr 2016
Hyundai Motor Company (Hyundai) is recalling certain model year 2015-2016 Sonata vehicles manufactured May 29, 2014 to February 11, 2016, 2017 Elantra vehicles manufactured January 12, 2016 to February 22, 2016, and one 2016 Sonata Hybrid vehicle manufactured October 15, 2015. I…
NHTSA campaign 16V232000
How do I fix P0118 on a 2017 Hyundai Elantra?
- Reconnect the ECT sensor connector
- Replace the ECT sensor with an OEM part
- Repair the broken ECT signal wire
- Clean corroded connector pins
About the 2015-2019 Hyundai Elantra
The 2015-2019 Hyundai Elantra was commonly sold with the following powertrains: 2.0L I4, 1.6L Turbo I4, 1.6L Hybrid I4. Common trims include SE, SEL, N Line, Limited.
P0118 vs P0117
These are the two ends of the same circuit:
- P0117 — ECT signal too low (sensor reads very high temperature like “300 °F”). Usually a shorted-to-ground wire or sensor failed closed.
- P0118 — ECT signal too high (sensor reads very low temperature like “−40 °F”). Usually an open circuit — disconnected, broken wire, or sensor open internally.
Why P0118 causes a hot engine to run rich
When the ECT signal goes missing or reads “very cold,” the ECM commands cold-start enrichment continuously — even on a hot engine. The result: fouled spark plugs, rich-running symptoms, possibly a hard start when the engine is actually warm because flooding occurs. This is why P0118 is worth fixing promptly even though it doesn’t look like a serious code.
Multi-sensor confusion: ECT vs IAT vs CHT
Modern engines may have multiple temperature sensors:
- ECT (Engine Coolant Temperature) — in coolant passage
- IAT (Intake Air Temperature) — in air intake tract
- CHT (Cylinder Head Temperature) — bolted to head, no coolant contact
- TFT (Transmission Fluid Temperature) — in transmission
Their codes are similar — P0118 (ECT high), P0113 (IAT high), P0119 (ECT erratic). Make sure the connector you are pulling is for the sensor referenced in the code.
P0118 on a 2017 Hyundai Elantra: frequently asked questions
What does diagnostic trouble code P0118 mean on a 2017 Hyundai Elantra?
P0118 is set when the engine control module reads the engine coolant temperature sensor signal voltage above the calibrated maximum — typically a reading that would represent an unrealistically cold coolant temperature (often −40 °F / −40 °C). This is the open-circuit fingerprint for the ECT sensor: a disconnected sensor, a broken signal wire, or a sensor failed open internally.
What are the symptoms of P0118 on a 2017 Hyundai Elantra?
Check Engine Light is illuminated. Temperature gauge reads zero or stays cold. Difficult cold start with rich-running symptoms. Cooling fans may run constantly (ECM thinks coolant is dangerously cold). Slightly reduced fuel economy. Cold-running engine doesn't warm up properly per the gauge. Possible hard start when the engine is hot (ECM commands cold-start enrichment)
What causes P0118 on a 2017 Hyundai Elantra?
Disconnected or unlatched ECT sensor connector (most-common). Broken or chafed ECT signal wire (open circuit) (common). Internally failed ECT sensor (element opened) (common). Corroded sensor connector pins (common). Damaged sensor body from coolant leak or freeze (occasional). Failed PCM signal input (rare) (rare)
Is it safe to drive a 2017 Hyundai Elantra with P0118?
In most cases a 2017 Hyundai Elantra stays drivable for short trips with P0118 active, but it should be diagnosed and repaired promptly — this is a moderate-severity code. Ignoring it can lead to further damage or a failed emissions test.