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P0118 on 2007-2016 Volvo S80 3.2L: Engine Coolant Temperature Sensor Causes and Fixes

On the Volvo S80 3.2L, code P0118 is almost always caused by a failed Engine Coolant Temperature (ECT) sensor. Because the sensor is integrated into the thermostat housing located under the intake manifold, the entire assembly is typically replaced. Expect to pay $100-$180 for the part. This is a moderately difficult DIY job due to the need to remove the intake manifold.

19 minutes to read 2007-2016 Volvo S80

Most Likely Cause

Failed Engine Coolant Temperature (ECT) Sensor / Thermostat Assembly

Difficulty

4/5

Est. Time

3.2 hrs

DIY Doable?

🔧 Shop

Shop Labor

$400 – $700

Parts Price

$100 – $180

⚠️ Drivable, but... — You can drive, but it's not recommended for long distances. The ECM will enter a failsafe mode, often assuming a default engine temperature, which leads to poor fuel economy, hard starting, and potentially long-term stress on the catalytic converter. The cooling fans will also run constantly at high speed as a protective measure, even after the engine is off, which can drain the battery.

Key Takeaways

P0118 on this Volvo means the engine computer thinks the engine is freezing cold due to a fault in the coolant temperature sensor circuit.
The most common symptom, besides the Check Engine Light, is the radiator fan running constantly at full speed.
The fix is to replace the entire thermostat housing assembly, which contains the sensor.
This is not a simple repair; the intake manifold must be removed to access the part, making it a 4/5 difficulty for DIY.
Always replace the intake manifold gaskets (PN 30777423) when performing this job to prevent future vacuum leaks.

The trouble code P0118 stands for "Engine Coolant Temperature (ECT) Sensor Circuit High Input". This means the Engine Control Module (ECM) is receiving a voltage signal from the ECT sensor that is higher than its normal operational range, typically over 4.9 volts. The ECM interprets this high voltage as an impossibly cold engine temperature, often defaulting to a reading like -40°F (-40°C). This indicates an open circuit, which is most commonly caused by a failed sensor, a break in the wiring, or a poor connection at the sensor plug.

What's Unique About the 2007-2016 Volvo S80

On the Volvo 3.2L SI6 engine, the Engine Coolant Temperature (ECT) sensor is not a separate, easily accessible part. Instead, it is integrated directly into the main thermostat housing assembly. This entire assembly is located underneath the intake manifold, making replacement a more involved job that requires removing the manifold for access. Because of this design, a P0118 code on this specific engine almost always leads to replacing the complete thermostat housing unit rather than just a simple sensor. This design is shared across all vehicles using the 3.2L SI6 engine.

🎬 Watch this overview of replacing the Volvo 3.2 thermostat housing assembly.

Symptoms You May Notice

Check Engine Light is on
Cooling fans run continuously at high speed, even after the engine is turned off.
Hard starting, especially when the engine is cold, as the ECM commands an overly rich fuel mixture.
Noticeably poor fuel economy.
Black smoke from the exhaust during a cold start due to the rich fuel mixture.
Rough or unstable idle.
Temperature gauge on the dashboard may read cold and not move, or show other erratic behavior.

⚠️ Don't Waste Money on the Wrong Fix

Replacing only the thermostat. On this engine, the sensor is part of the housing assembly, so replacing a standalone thermostat (if one could be sourced) would not fix an electrical code like P0118.
Assuming the car is actually overheating. While the fans run constantly, the P0118 code itself indicates an electrical fault (impossibly cold reading), not a true overheating condition.

Most Likely Causes

Failed Engine Coolant Temperature (ECT) Sensor / Thermostat Assembly 🔴 High Probability The ECT sensor is integrated into the thermostat housing, which is a common failure point on the SI6 engine. The plastic housing and internal sensor are subject to constant heat cycles, leading to eventual failure. The entire unit is replaced as a single assembly.
How to confirm: Use an OBD-II scanner to check live data. A temperature reading of -40°F or -40°C is a definitive sign of an open circuit fault pointing to the sensor or its wiring. Final confirmation requires testing the sensor directly, which necessitates removing the intake manifold for access.
Typical fix: Replace the entire thermostat housing assembly, which includes the thermostat, housing, and new integrated ECT sensor. It is critical to also replace the intake manifold gaskets at the same time.
Est. part cost: $100-$180
Damaged Wiring or Connector 🟡 Medium Probability The wiring harness is located under the intake manifold in a high-heat area, making it susceptible to becoming brittle and damaged over time. Oil leaks from the nearby PCV system or vacuum pump can also degrade the wiring insulation, leading to shorts or breaks.
How to confirm: After removing the intake manifold, visually inspect the connector and wiring going to the thermostat housing for any signs of corrosion, breaks, or loose pins. Use a multimeter to check for a 5-volt reference signal 🎬 Learn how to test and diagnose a P0118 sensor circuit. and a good ground at the connector. If either is missing, the problem is in the harness, not the sensor.
Typical fix: Repair the damaged section of the wiring harness or replace the connector pigtail. Ensure the repair is well-insulated to protect against future heat damage.
Est. part cost: $15-$50

Rare But Worth Checking

Faulty Engine Control Module (ECM): This is extremely rare. This should only be considered after a certified technician has definitively ruled out the sensor, wiring, and connectors as the cause of the problem.

Diagnosis Steps

Connect an OBD-II scanner and confirm P0118 is the active code. Check for any other related codes.
View the live data stream. Look at the Engine Coolant Temperature (ECT) reading. A value of -40°F or -40°C strongly indicates an open circuit in the ECT sensor system.
As a simple check, compare the cold ECT reading to the Intake Air Temperature (IAT) reading with the engine off. They should be very close. A large discrepancy points to the ECT circuit.
Prepare to access the thermostat housing. This requires the removal of the engine intake manifold. 🎬 Watch a step-by-step video on removing the Volvo S80 intake manifold. This is a multi-hour job.
Once the manifold is removed, carefully inspect the ECT sensor connector (part of the thermostat housing) and its wiring harness for any visible damage, corrosion, oil contamination, or loose pins.
If no visual damage is found, disconnect the sensor. Use a multimeter to test for a 5-volt reference and a good ground at the connector pins with the key on, engine off.
If the 5V reference and ground are present, the fault is almost certainly the ECT sensor itself. Since it's integrated, the entire thermostat assembly must be replaced.
If voltage or ground is missing, the wiring harness is faulty. Trace the wiring back towards the ECM to find and repair the break or short.
After replacing the thermostat assembly and intake manifold gaskets, clear the trouble code and perform a drive cycle. Monitor the live ECT data to ensure it rises to normal operating temperature (typically 190-210°F) and the cooling fans cycle correctly.

Parts You'll Likely Need

Engine Coolant Thermostat Assembly (OEM #31355151) — This is the primary cause of P0118 on the 3.2L engine, as it contains the integrated ECT sensor, thermostat, and housing in one unit.
Trusted brands: Volvo (Genuine), Mahle, Behr, Wahler
OEM price range: $150-$185
Aftermarket price range: $90-$130
Intake Manifold Gaskets (OEM #30777423) — The intake manifold must be removed to access the thermostat housing. The gaskets are considered a one-time use item and must be replaced to prevent vacuum leaks after the repair.
Trusted brands: Volvo (Genuine), Victor Reinz, Elring
OEM price range: $50-$70
Aftermarket price range: $25-$40

Platform-Specific Known Issues

Access Requires Intake Manifold Removal: Unlike many vehicles where the ECT sensor is easily accessible, on the Volvo 3.2L SI6 it is buried under the intake manifold. This significantly increases the labor time and complexity of the repair, turning a simple sensor replacement into a more involved job.

Mechanic-Grade Diagnostic Values

ECT Sensor Resistance vs. Temperature — expected: Approx. 5.6 kOhms at 32°F (0°C), ~2.0-3.0 kOhms at 68°F (20°C), ~318 Ohms at 176°F (80°F), and ~184 Ohms at 212°F (100°F).. Failure: Infinite resistance (open circuit) or a reading that does not change as temperature changes. A reading of near-zero ohms indicates a short circuit.
ECT Sensor Connector Voltage (Key On, Engine Off) — expected: One pin should have a 5-volt reference from the ECM, and the other should be a sensor ground.. Failure: Absence of the 5V reference or a faulty ground points to a wiring or ECM issue, not a sensor failure.

Hidden / Shadow Codes Worth Checking

ECM-P011817: This is the Volvo-specific format for the generic P0118 code. The suffix '17' often indicates 'Circuit voltage above threshold'. Seeing this code in VIDA confirms the ECM is seeing a voltage higher than the expected maximum, reinforcing the diagnosis of an open circuit. (see via Volvo's VIDA diagnostic software or a compatible high-end professional scanner.)

Wiring & Ground Locations

ECT Sensor Connector — Plugged into the thermostat housing, which is located on the left side (driver's side for US models) of the engine block, underneath the intake manifold.. This is the primary connection point to test. Corrosion, oil contamination, or loose pins here are a common cause of the 'High Input' signal.
G89 — A ground point located in the left front of the engine compartment.. This ground serves various engine components. While not exclusively for the ECT, a corroded or loose connection at this point can introduce electrical noise or a floating ground, potentially affecting sensor readings.

Real Owner Repair Stories

VolvoForums user 'rspi' (1998 Volvo S70 (P80 chassis, but same sensor principle)) — Overheating condition occurred, which damaged the original temp sensor. A new sensor was installed.
❌ Tried (didn't work) A brand new (likely aftermarket) ECT sensor was installed but failed within a week, causing the same P0118 symptoms to return.
✅ What actually fixed it Installing a used ECT sensor sourced from a junkyard resolved the problem long-term. This suggests potential quality control issues with some new aftermarket sensors, making a used OEM part a viable alternative.

OEM Part Supersession History

30774489 → 31355151 — Standard part revision and consolidation by Volvo.
Heads up: None. The new part number (31355151) is a direct replacement for the old one (30774489).

Model Year Variations Within This Range

2011-2016: For the 2011 model year, the 3.2L inline-6 engine received a minor power increase from 235 hp to 240 hp. This change did not affect the cooling system, thermostat housing part number, or the diagnosis for code P0118.

Diagnostic Flowchart

The P0118 code indicates a high voltage/open circuit in the Engine Coolant Temperature (ECT) sensor. On the Volvo SI6 engine, this sensor is integrated into the thermostat housing and buried under the intake manifold.

With the engine cold (off for 8+ hours), compare the ECT reading to the Intake Air Temperature (IAT) reading. Are they significantly different?

To access the sensor on the SI6 engine, you must remove the intake manifold. Have you removed the manifold and inspected the thermostat housing area?

Inspect the ECT connector and wiring. Is there evidence of oil contamination from the Brake Vacuum Pump or PCV system?

→ Oil from a leaking Brake Vacuum Pump (common on S80s over 80k miles) can degrade the ECT connector. Clean the connector with electronic cleaner and replace the vacuum pump seals to prevent recurrence.

With Key On Engine Off (KOEO), use a multimeter to test the harness connector. Do you have a 5V reference and a solid ground?

→ The wiring harness is intact. The internal thermistor in the integrated thermostat housing has failed open. Replace the entire thermostat assembly (PN 31355151) and install new intake manifold gaskets.

Trace the wiring back toward the ECM. Is the harness brittle or cracked in the high-heat zone under the manifold?

→ Repair the damaged wiring or replace the connector pigtail. Use heat-resistant insulation, as the SI6 engine bay temperatures are high. Re-test for 5V reference before reassembling the manifold.

→ If the harness tests open but looks fine, the break may be closer to the ECM or within the ECM itself. Perform a continuity test from the ECT connector pins directly to the ECM pins.

→ On the 3.2L B6324S engine, there is no shortcut. You must remove the intake manifold to reach the integrated ECT sensor. Ensure you have new intake manifold gaskets ready for reassembly.

→ The fault may be intermittent. Clear the code and monitor the harness while the engine reaches operating temperature (190-210°F). If fans run at high speed constantly, the ECM is in failsafe mode.

Wiggle the wiring harness near the back of the engine while watching live data. Does the temperature jump?

→ This indicates a loose pin or partial break in the harness. Proceed to remove the intake manifold to perform a permanent wiring repair at the thermostat housing connector.