Engine Temperature / Overheating Warning Light On
A red engine temperature light (or the temperature gauge climbing into the red) means your engine is overheating, and that can warp the cylinder head or blow the head gasket if you keep driving. The cooling system is either low on coolant, not circulating it, or not shedding heat. This is a stop-driving situation: continuing can turn a cheap fix into a new engine.
Trouble codes you may see
If you scan the car, these are the OBD-II codes most often behind this symptom:
Common causes
- 1
Low coolant level
Often the starting point, caused by a leak from a hose, radiator, water pump, or the reservoir. Low coolant can't carry away enough heat. Never open a hot radiator cap, wait until it cools.
- 2
Failed thermostat
A thermostat stuck closed traps coolant in the engine and causes rapid overheating; stuck open can cause running-too-cool codes like P0128.
- 3
Failing water pump
If the pump's impeller is worn or the pump leaks, coolant doesn't circulate and temperatures spike, especially at higher RPM.
- 4
Cooling fan not running
A bad electric fan, fan relay, or fan-control circuit (P0480 area) lets the engine overheat in traffic or at idle even though it's fine on the highway.
- 5
Coolant leak from hose, radiator, or head gasket
Cracked hoses, a clogged or leaking radiator, or a blown head gasket all bleed off coolant or let combustion gases into the system.
- 6
Faulty coolant temperature sensor
A bad ECT sensor (P0117/P0118) can cause a false overheat reading or keep fans from running correctly.
What to do
Treat this as an emergency: turn off the A/C, turn the heater on full to pull heat from the engine, and pull over to shut the engine off as soon as it's safe. Let it cool at least 30-60 minutes before touching the radiator cap, then check the coolant level once cool and top up if low. If it overheats again or you see steam or leaking coolant, have it towed, do not keep driving, because overheating can crack the head or destroy the engine.
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