P0118 on a 2017 Subaru Outback
Coolant Temp Sensor High Input
P0118 on a 2017 Subaru Outback 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 Subaru Outback?
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 Subaru Outback generation — the symptoms, causes, and diagnostic steps below apply to every model year from 2015 through 2019.
Is it safe to drive a 2017 Subaru Outback with P0118?
In most cases a 2017 Subaru Outback 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 Subaru Outback?
- 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 Subaru Outback?
| 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 Subaru Outback
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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 Subaru Outback
Owner-reported safety complaints and official recalls filed with the U.S. National Highway Traffic Safety Administration for the 2017 Subaru Outback. Use these to gauge how common a problem is on your specific vehicle before you start chasing Subaru Outback diagnostics.
- POWER TRAIN 46
- ENGINE 42
- ELECTRICAL SYSTEM 391
- VISIBILITY/WIPER 205
- UNKNOWN OR OTHER 175
4 active recalls
- AIR BAGS: AIR BAG/RESTRAINT CONTROL MODULE Dec 2019
Subaru of America, Inc. (Subaru) is recalling certain 2016-2017 Outback vehicles. A replacement air bag control module may have been installed that is not compatible with the passenger air bag module, possibly affecting air bag deployment.…
NHTSA campaign 19V910000 - SUSPENSION Aug 2016
Subaru of America, Inc. (Subaru) is recalling certain model year 2017 Outback vehicles manufactured June 20, 2016, to June 23, 2016. The affected vehicles may have improperly tightened attaching bolts for the front left and right brake calipers, wheel hubs, and the right stabili…
NHTSA campaign 16V576000 - STEERING:COLUMN Oct 2016
Subaru of America, Inc. (Subaru) is recalling certain model year 2017 Legacy and Outback vehicles manufactured September 21, 2016, to September 23, 2016. In the affected vehicles, the knee guard bracket may not be properly attached to the steering beam assembly.…
NHTSA campaign 16V716000 - STEERING:COLUMN May 2016
Subaru of America, Inc. (Subaru) is recalling certain model year 2016-2017 Legacy and Outback vehicles manufactured February 29, 2016, to May 6, 2016. The steering column on the affected vehicles may have been improperly machined, and as a result, turning the steering wheel may…
NHTSA campaign 16V292000
How do I fix P0118 on a 2017 Subaru Outback?
- 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 Subaru Outback
The 2015-2019 Subaru Outback was commonly sold with the following powertrains: 2.5L H4, 2.4L Turbo H4, 3.6L H6. Common trims include Base, Premium, Limited, Touring, Wilderness, Onyx Edition.
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 Subaru Outback: frequently asked questions
What does diagnostic trouble code P0118 mean on a 2017 Subaru Outback?
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 Subaru Outback?
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 Subaru Outback?
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 Subaru Outback with P0118?
In most cases a 2017 Subaru Outback 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.