P2184: Engine Coolant Temperature Sensor 2 Circuit Low
What to do
Expect the cooling fans to run constantly, and possibly hard starting or rough running when cold. The engine is not actually overheating — the module is reading a fault as extreme heat, which is the reverse of how it sounds. Driveable, but the constant fan operation drains the battery on short trips and the incorrect fuelling is hard on a cold engine, so it is worth attending to.
What this code means
The second coolant sensor circuit reads below its valid voltage range — normally a short to ground, or a sensor that has failed to a very low resistance.
The direction of a coolant sensor code is the reverse of what most people expect, and it causes real confusion. These sensors are negative-temperature-coefficient thermistors: their resistance falls as they get hotter. A low circuit voltage therefore corresponds to a high indicated temperature. So a "circuit low" code means the module is being told the engine is extremely hot — often implausibly so, which is what makes it a circuit fault rather than an overheating report.
The practical consequence is immediate and visible: the cooling fans will usually run continuously, from the moment the ignition is switched on and regardless of actual temperature, because the module is acting on the reading it has. Fans roaring on a stone-cold engine is a strong signal for this code and its equivalents.
The module will normally also assume a hot engine for fuelling purposes, which suppresses cold-start enrichment. On a genuinely cold engine that produces hard starting and rough running until it warms, and on a diesel it can suppress the glow plugs entirely.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Faulty engine coolant temperature sensor · easy
- Coolant leak into the sensor connector · easy
Less common
- Damaged wiring harness · moderate
- Corroded or loose connector · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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