Chevrolet Blazer Coolant Temperature Sensor: A Comprehensive Guide (1987-2005)
Running rich or starting hard? Your Blazer's Coolant Temperature Sensor could be the culprit.
- First, confirm your Blazer's year to know if you have one sensor (1999-2005) or two (1987-1998).
- Common failure symptoms include poor gas mileage, black smoke, hard starting, and a rough idle.
- Replacement is an easy DIY job that can be done in under 30 minutes with basic tools.
- For reliability, consider spending a few extra dollars on an OEM-grade brand like ACDelco.
Is a Faulty Coolant Temp Sensor Causing Your Blazer's Problems?
If your 1987-2005 Chevrolet Blazer is getting poor gas mileage, running rough, or has a hard time starting, a bad Engine Coolant Temperature (ECT) sensor is a likely cause. This sensor's signal affects many critical engine systems, and when it sends incorrect information, it can lead to a variety of confusing symptoms. Because it is an inexpensive and simple part to replace, it's a common first step in troubleshooting these issues.
Critical: How Many Sensors Does Your Blazer Have?
Before buying any parts, you must know which system your Blazer uses. This is the most common mistake owners make.
- 1987-1998 Models: These trucks have TWO separate units. The main two-wire ECT sensor for the computer is on the front of the intake manifold, near the thermostat housing. A separate one-wire temperature sender for the dashboard gauge is on the driver's side cylinder head.
- 1999-2005 Models: GM simplified the system to a SINGLE two-wire sensor. This one part sends temperature information to both the computer and the dashboard gauge. It is located on the driver's side cylinder head.
If your temperature gauge is the only problem on a pre-1999 model, you likely need the one-wire sender, not the main ECT sensor.
Symptoms of a Failing Coolant Temperature Sensor
- Poor Fuel Economy: This is a classic symptom. If the sensor wrongly tells the computer the engine is always cold, the computer will constantly command a rich fuel mixture, wasting gas.
- Black Smoke from Exhaust: A sign of an overly rich fuel mixture, where unburnt fuel is pushed out the tailpipe.
- Check Engine Light: A faulty sensor will often trigger a check engine light with codes like P0117 (circuit low input) or P0118 (circuit high input).
- Hard Starting: The engine may be difficult to start, either when cold or when fully warmed up, because the fuel mixture is incorrect for the actual engine temperature.
- Rough Idle or Stalling: After warming up, the engine may stumble, idle poorly, or stall if the fuel mixture is too rich.
- Inaccurate Temp Gauge: On 1999-2005 models, the gauge may read cold all the time, jump to hot, or not move at all.
Choosing the Right Aftermarket Part
For a sensor that plays such a key role in engine management, part quality matters. While many aftermarket parts offer good value, reliability can vary.
- OEM/Premium Brands (e.g., ACDelco, Delphi): ACDelco is the original equipment manufacturer for GM. Brands like ACDelco or Delphi are widely recommended by mechanics for their reliability and accuracy. For a critical sensor, spending a few extra dollars on a trusted brand is a wise investment to avoid future headaches.
- Standard Aftermarket Brands (e.g., Replacement): Standard aftermarket sensors are a cost-effective option that can restore function. For a vehicle of this age, a standard replacement is a common repair. However, be aware that budget-tier electronics can sometimes have a shorter lifespan or less precise readings compared to their premium counterparts.
Pro Tip: Check the Connector First
On older trucks like the Blazer, the plastic electrical connector and wiring can become brittle and fail. A poor connection can cause the exact same symptoms as a bad sensor. Before replacing the part, inspect the connector for corrosion or damage. Sometimes, simply cleaning the contacts or replacing a damaged connector pigtail is all that's needed.
| Part/Service | Estimated Cost |
|---|---|
| New OEM Sensor (ACDelco) | $15 - $30 |
| New Aftermarket Sensor | $18.79 |
| Shop Labor | $50 - $100 |
Frequently Asked Questions (FAQ)
Where is the coolant temperature sensor on my Blazer?
It depends on the year. For 1987-1998 models, the main sensor (for the computer) is on the intake manifold near the thermostat housing. For 1999-2005 models, the single sensor is on the driver's side cylinder head.
My temperature gauge doesn't work. Is it the ECT sensor?
On a 1999-2005 model, yes, it is likely the same sensor. On a 1987-1998 model, probably not. The gauge is operated by a separate, one-wire temperature sender located on the cylinder head.
Can a bad ECT sensor cause my Blazer to not start?
Yes, it can cause a hard start or extended cranking. If the sensor tells the computer the engine is extremely hot or cold, the computer will create a fuel mixture that won't ignite properly.
Are there any recalls for the coolant temperature sensor on my Blazer?
No, as of early 2026, there are no specific recalls from the NHTSA for the engine coolant temperature sensor on the 1987-2005 Chevrolet Blazer. Failures are typically due to the age and mileage of the vehicle.
Technical Specifications
OEM Part Numbers: 213-928
Varies by year. 1987-1998 models use a two-wire sensor for the ECU and a one-wire sender for the gauge. 1999-2005 models use a single two-wire sensor for both ECU and gauge.
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.
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