Cause
Blocked or restricted radiator
A radiator or heat exchanger can no longer shed the heat it was sized for — blocked on the outside by debris, or restricted on the inside by deposits.
The two kinds of blockage look identical on a gauge and need completely different work, so telling them apart comes first. Outside is leaves, insects, road film, mud or a plastic bag against the core — and on modern vehicles, a stack of heat exchangers mounted one behind another, where the debris collects invisibly between them. Inside is scale, casting sand, corrosion products or the remains of a stop-leak additive, which narrow the tubes.
The outside case is the commoner one and the cheaper one by a wide margin, and it is genuinely worth looking at before anything else: a torch through the core from the front tells you a great deal for nothing. The inside case usually announces itself differently — a radiator with blocked passages runs cold in patches, which can be felt by hand across the core once warm, where a healthy one is evenly hot.
The symptom pattern is the diagnostic gift. A restricted radiator copes at speed and fails in traffic, because airflow at 70 mph hides a great deal that idling does not. So "it only overheats when I stop" points here or at the fan, and "it overheats on the motorway" points somewhere else entirely — at flow, at the pump, or at a thermostat.
On an electrified vehicle this matters in more places than it used to: the traction battery and the power electronics have their own heat exchangers, often stacked in the same airflow, and one blocked core can limit charging rate or drive power on a car whose engine cooling is perfect.
Typically a moderate job.
Some of these codes mean you should stop driving
2 of the 9 codes this can cause indicate a fault where continuing to drive risks damage or is unsafe. Which one you have matters more than the cause does — read the code's own page before deciding.
Codes this can cause (9)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0217 Engine Coolant Over Temperature Condition Likely for this code Stop driving Critical
- P00B2 Radiator Coolant Temperature Sensor Circuit Range/Performance Moderate
- P0298 Engine Oil Over Temperature Stop driving Critical
- P0C31 Inverter B Cooling System Performance High
- P0D6F Air Conditioning Compressor Motor Current High High
- P0EA7 Auxiliary Cooling System Performance High
- P2181 Cooling System Performance Moderate
- P2183 Engine Coolant Temperature Sensor 2 Circuit Range/Performance Moderate
- P2340 Cylinder 5 Above Knock/Combustion Vibration Sensor Threshold High
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.
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