P0597

Thermostat Heater Control Circuit/Open

Car Fault Codes Cooling & lubrication

Can you still drive? Yes, normally

Who can fix it? Needs a workshop

Typical repair time 30 minutes – 2.5 hours

Typical cost SAR 100 to 1,500

What it means

Some engines use an electronically controlled thermostat with a small heater that the engine computer switches on to open it early and lower engine temperature under load. The computer has found this heater circuit open or not responding, so it can no longer control temperature this way.

Symptoms4

Check engine light on.
Engine temperature slightly higher than usual when driving under load or in heat.
Slight increase in fuel use or change in engine performance.
Often no clear symptoms other than the light.

Possible causes5

Failed heating element inside the thermostat.
Connector corroded by coolant leaking into it.
Open heater wiring.
Blown fuse in the heater supply circuit.
Fault in the driver circuit inside the engine computer (rare).

How to diagnose5

Inspect the connector for coolant or corrosion.
Command the heater on with a scan tool if possible and watch the response.
Measure the heating element resistance and compare it with the manufacturer specification; infinite resistance means an open.
Check the fuse and the supply voltage at the connector.
Check continuity of the wire between the connector and the computer.

How to fix5

Replace the fuse after confirming there is no short.
Clean or replace the connector and fix any coolant leak.
Repair broken wiring.
Replace the complete electronic thermostat, since the heater is part of it on most vehicles.
Clear the codes and confirm engine temperature stays in the normal range.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for a connector or wire fault, and rises when the electronic thermostat is replaced, since it costs more than a standard one and the coolant must be drained.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Does this code cause overheating?

It does not usually cause boiling, because the thermostat still works in the conventional way, but temperature may run slightly higher under load. Watch the temperature gauge.

Can the heater be replaced on its own?

On most vehicles no, because the heater is built into the thermostat, so the whole unit is replaced.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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