P0115: Engine Coolant Temperature Sensor 1 Circuit
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Short trips only - cooling fan behaviour and cold-start fuelling both depend on this sensor.
Symptoms
- Cooling fans running constantly or not at all
- Hard cold starts
- Temperature gauge behaving oddly
Likely causes, most common first
- Engine coolant temperature sensor failed
- Broken or chafed wiring
- Connector corrosion
- Sensor loose in its port
Read P0115 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P0115 is the general circuit fault for the engine coolant temperature sensor. Almost everything the engine computer decides is temperature-dependent - fuel enrichment, ignition timing, fan control, and on many cars the transmission's shift and lock-up strategy - so a bad reading has effects far from the engine bay.
Do not confuse this sensor with the one feeding the dashboard gauge; most cars have two, and the gauge can look perfectly normal while the computer is being lied to. The sensor for the computer is usually the one with the multi-wire connector.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P0115
“My 2005 dodge ram has been stalling while idiling at stop lights/signs. It was throwing a code of p0115. I have now replaced the throttle body, egr valve, thermostat, ect sensor, and cam sensor . The truck is at the dodge dealers for now 9 days. The service tech are pulling out their hair trying to find the issue. I see that other dodge trucks and cars have the same problem. So why is there not a recall on this item? This is a safety concern. Especially when the truck dies while turning I could get hit. I have been dealing with this on my own for the past three months. Now the service techs are at their wits end too.”2005 Dodge Ram 1500 · Nov 2016 · 126,000 mi
Cars that report P0115 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P0115?
Short trips only - cooling fan behaviour and cold-start fuelling both depend on this sensor.
How much does it cost to fix P0115?
Typical US repair costs range from $60 for the simplest fix (coolant temperature sensor) to $250 in the worst case. The right number depends on which cause your car has - see the causes list.
Related codes
The codes closest to P0115. They often appear together, and telling them apart is usually what narrows the diagnosis.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.