Engine Coolant Temperature Sensor Guide for 1998-2000 Volvo S70
Is your S70 running rough, getting bad gas mileage, or showing a check engine light? Your coolant sensor might be the culprit.
- A bad ECT sensor commonly causes a check engine light, poor gas mileage, and rough running on the S70.
- Replacement is straightforward and located under the thermostat housing; it's a good DIY project.
- For reliability, choose a quality aftermarket brand like Beck Arnley or Standard Ignition over budget options which have mixed reviews.
- Always replace the thermostat at the same time as the sensor to avoid future problems, as a lazy thermostat can trigger the same error codes.
Is Your S70's Coolant Temp Sensor Failing?
A bad Engine Coolant Temperature (ECT) sensor can cause a surprising number of problems. Because the sensor's reading affects so many engine functions, a false signal can confuse the car's computer. The 1998-2000 Volvo S70 uses one main sensor for both the computer and the temperature gauge on your dashboard. If it fails, you'll likely notice it.
Common Symptoms of a Bad ECT Sensor:
- Check Engine Light: This is often the first sign. You may see codes like P0115, P0116, P0117, or P0118.
- Poor Fuel Economy: If the sensor tells the computer the engine is always cold, the computer will inject extra fuel, wasting gas.
- Black Smoke from Exhaust: This is a sign of a rich fuel mixture (too much fuel), which can be caused by a bad sensor reading.
- Hard Starting: The engine may be difficult to start, especially when it's already warm.
- Rough Idle: The engine may idle poorly or feel shaky because the fuel mixture is incorrect.
- Cooling Fans Run Constantly: As a fail-safe, the ECU may run the cooling fans at full speed if it gets an illogical signal from the sensor.
- Engine Overheating: In some cases, a faulty sensor might fail to trigger the cooling fans when needed, leading to overheating.
Choosing the Right Aftermarket Sensor
When replacing the ECT sensor on your S70, you have a choice between Genuine Volvo parts and a variety of aftermarket brands. For a critical sensor like this, quality matters. A cheap, inaccurate sensor can cause the same running problems as a failed one.
Brand Quality Tiers for Your Volvo:
- Premium Aftermarket (Good): Brands like Beck Arnley, Standard Ignition (SMP), and Facet are generally considered reliable choices. They focus on meeting or exceeding original specifications and offer a good balance of quality and price. Beck Arnley, in particular, is known for sourcing parts from various OEM suppliers.
- Economy Aftermarket (Use with Caution): Brands like URO Parts, Four Seasons, and other unbranded options fall into the budget category. While the low price is appealing, forum discussions show mixed results for electronic parts from these brands. Some owners report premature failures or inaccurate readings right out of the box. These may be suitable if budget is the absolute top priority, but be aware of the potential risks.
Pro Tip: Many times, a check engine light for the ECT sensor on these Volvos is actually caused by a failing thermostat that doesn't let the engine warm up quickly enough. It is highly recommended to replace the thermostat (use a quality OEM or Behr unit) at the same time as the sensor for best results.
Cost of Replacing the Engine Coolant Temperature Sensor
| Part Type | Estimated Cost |
|---|---|
| New Genuine Volvo | $65 - $115 |
| New Aftermarket | $21.40 - $68.04 |
| Shop Labor | $50 - $100 |
Frequently Asked Questions
Where is the coolant temperature sensor located on my 1998-2000 S70?
The sensor is located on the thermostat housing, which is on the driver's side of the engine, right below where the large upper radiator hose connects to the engine. It is screwed into the housing and has a two-wire electrical connector.
Can I replace this sensor myself?
Yes, this is a very DIY-friendly job for someone with basic tools. You will need to drain a small amount of coolant, remove the upper radiator hose for access, remove the two bolts on the thermostat housing, and then you can unscrew the old sensor with a 19mm wrench. The whole process typically takes less than an hour.
What happens if I don't replace a bad sensor?
Driving with a bad ECT sensor can lead to several issues. You will experience poor fuel economy, which costs you money. A constantly rich fuel mixture can foul your spark plugs and potentially damage your catalytic converter over time. It can also make the car unreliable and hard to start.
Are there any recalls for this part?
No, there are no specific recalls or technical service bulletins (TSBs) from the National Highway Traffic Safety Administration (NHTSA) for the engine coolant temperature sensor on the 1998-2000 Volvo S70.
Technical Specifications
OEM Part Numbers: 9186486 3545031
Location: Thermostat Housing. Connector: 2-Pin Female. Wrench Size: 19mm.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Volvo S70: