Volvo 740 Engine Coolant Temperature Sensor: A Complete Guide (1985-1992)
Solve rough idle, poor fuel economy, and hard starts by understanding this critical engine sensor in your 740.
- Your Volvo 740 has two temp sensors; confirm you are replacing the two-wire sensor for the engine computer, not the single-wire sensor for the dash gauge.
- For reliable performance, choose an OEM-quality brand like Bosch. Cheaper sensors are known to have incorrect values that will not fix the problem.
- Before buying, use the built-in diagnostic reader to check for fault code 1-2-3, which points directly to this sensor.
- Replacement is difficult due to the sensor's location under the intake manifold; removing the manifold is often the easiest approach.
Is It the Right Sensor? Your 740 Has Two
Before you buy a part, it's critical to know that the Volvo 740 has two separate coolant temperature sensors located under the intake manifold. Ordering the wrong one is a common mistake.
- Engine Coolant Temperature (ECT) Sensor: This is the sensor for the engine computer (ECU). It has a two-prong electrical connector and directly affects how your engine runs. It is typically located under the #3 intake manifold runner (counting from the front of the engine). This is the part this guide focuses on.
- Temperature Sender/Sensor: This sensor is only for the temperature gauge on your instrument cluster. It usually has a single spade-style connector. A failure of this part will only cause your dash gauge to read incorrectly; it will not affect engine performance.
Confirm the Part
Always visually inspect the sensor you are replacing to ensure you are buying the correct one. The ECU sensor has two pins for the fuel and ignition computers; the gauge sender often has only one.
Symptoms of a Failing ECT Sensor
When the main ECT sensor fails, the engine's computer receives incorrect information, or no information at all. The computer will then default to a fixed temperature value, which can cause a variety of noticeable problems.
- Hard Starting, Especially When Warm: The engine may start perfectly when cold but become very difficult to start after it has been driven and parked for a short time.
- Rough or "Hunting" Idle: The engine idle may surge up and down as the computer struggles to find the correct fuel mixture.
- Poor Fuel Economy: A failed sensor often tells the computer the engine is colder than it is, causing it to run a rich fuel mixture all the time and burn more gas.
- Black Smoke from Exhaust: This is a sign of an overly rich fuel mixture, where unburned fuel is being sent out the tailpipe.
- Check Engine Light: On these pre-OBD-II Volvos, a fault in the ECT sensor circuit will trigger the check engine light and store a specific fault code. The most common code for this issue is 1-2-3.
Choosing the Right Aftermarket Part: Brand Quality Matters
For a critical sensor like the ECT, brand quality is important. Cheaper aftermarket sensors are known to have incorrect resistance values, which means they won't send the right temperature signals to the computer. This can lead to the same running problems you were trying to fix. Volvo owners on forums strongly recommend sticking with OEM or high-quality European brands.
Brand Tiers for Your Volvo 740
| Tier | Brands | Assessment |
|---|---|---|
| OEM / Premium | Bosch | Bosch was the original equipment manufacturer for the fuel injection system on these Volvos. Choosing Bosch ensures that the sensor has the correct resistance curve for your car's computer. This is the most recommended and reliable option. |
| Reputable Aftermarket | Hella, Facet | These are well-known European brands that generally produce quality components. They are a solid choice if an OEM part is not available, though some users have reported occasional premature failures. |
| Standard Aftermarket | Four Seasons, Standard Ignition, Walker Products, etc. | These brands offer a budget-friendly option. However, for this specific part, there is a higher risk of incorrect calibration which can cause persistent performance issues. Use with caution; it may be a gamble. |
Pro Tip: Check Your Codes First
Your 1985-1992 Volvo 740 has a built-in diagnostic system (OBD-I). Under the hood, near the driver's side strut tower, you'll find a small black box with an LED, a button, and a probe. By inserting the probe into socket #2 (for the fuel system) and pressing the button, you can read fault codes. A code of 1-2-3 points directly to a fault in the coolant temperature sensor circuit. Always check for codes before replacing parts.
🎬 See how to access and replace the sensor on a 1990 model.Frequently Asked Questions (FAQ)
Where is the engine coolant temperature sensor located?
The ECT sensor for the computer is located on the driver's side of the cylinder head, underneath the intake manifold. It is typically positioned below the third intake runner. It is difficult to see and reach from above.
🎬 Watch this video for a clear view of the sensor's location.Is it difficult to replace the ECT sensor myself?
Yes, this can be a frustrating job. The sensor's location under the intake manifold provides very little room to work. While some have managed to change it with swivels and extensions, many mechanics and DIYers find it easier to remove the intake manifold for access. If you remove the manifold, you should replace the intake manifold gasket at the same time.
🎬 Watch this step-by-step replacement guide for Volvo red block engines.My dash temperature gauge doesn't work. Is this the right part to fix it?
No. This sensor is for the engine computer. The dashboard gauge uses a separate, single-wire sensor that is also located under the intake manifold, usually near the #2 cylinder. A faulty gauge is caused by a bad gauge sensor, a problem in the wiring, or the gauge itself.
Are there any recalls for the Volvo 740 coolant temperature sensor?
No, there are no recalls or technical service bulletins (TSBs) from Volvo or the NHTSA for this specific part on the 1985-1992 Volvo 740.
Helpful Videos
Technical Specifications
OEM Part Numbers: 1346030 1362645 346030 1332396
This is a two-terminal thermistor sensor that provides temperature data to both the fuel (LH) and ignition (EZK) control units. On LH 2.4 systems (1989+), each pin provides a separate signal, grounding through the sensor body. The OEM Bosch part number is often 0280130032.
We Have This Part in Stock
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 740: