P0598 – Thermostat Heater Control Circuit Low (OBD2)
P0598 means "Thermostat Heater Control Circuit Low". The voltage the control unit measures in the map-controlled thermostat heater circuit is below the permitted minimum. For a sensor this usually means the signal wire is shorted to ground or the reference voltage is missing; for an actuator, that its control wire is shorted to ground.
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P0598 quick summary
| Fault code | P0598 |
|---|---|
| Meaning | Thermostat Heater Control Circuit Low |
| System | Powertrain (Engine & Transmission) |
| Vehicles | Generic OBD2 |
| Severity | Low |
| Can I drive? | Yes. The thermostat still opens mechanically. Watch the temperature on long climbs and towing. |
| Repair cost | €60 – €500 |
How the map-controlled (electric) thermostat works
Some engines use a thermostat with an electric heating element, so the control unit can open it earlier under load; these codes cover the heater's control circuit.
A map-controlled thermostat works like a normal wax thermostat but has a built-in heating element. When the engine is under high load, the control unit heats the wax so the thermostat opens earlier and the engine runs cooler; at part load it keeps the engine warmer for efficiency.
Codes P0597–P0599 report an open, low or high fault in the heater control circuit. The thermostat still works mechanically, but the engine runs at a higher temperature under load.
The heater is part of the thermostat housing, so a failed heater usually means replacing the thermostat. Corroded connectors are also common because the connector sits near the coolant.
On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16982 (P0598). Both numbers mean the same fault.
Symptoms of P0598
- Check Engine light on
- Engine temperature slightly higher under load
- Usually no driving symptoms
- Sometimes coolant temperature codes
Most common causes of P0598 (most likely first)
Mechanic's Pro Tip
Map-controlled thermostats are often replaced together with the coolant and the housing seal – use the manufacturer's coolant and the correct bleeding procedure.
1.Signal or control wire shorted to ground
Most likelyLook for chafed insulation where the harness touches the engine, exhaust brackets or body edges.
2.Missing 5 V reference or supply voltage
An open reference wire or a shorted sensor elsewhere on the same reference circuit can pull it down.
3.Internal short in the map-controlled thermostat heater
4.Failed heating element in the thermostat
5.Corroded connector or coolant in the connector
6.Wiring fault
7.Blown fuse
Step-by-step diagnostic guide
- 1
Read codes
Read all codes and check for related coolant temperature codes.
- 2
Measure the signal voltage
With the ignition on and the map-controlled thermostat heater plugged in, back-probe the signal wire. Then unplug it and check the reference/supply and ground wires separately.
Multimeter: Signal near 0 V = short to ground or no reference. Reference wire: about 5 V with ignition on. Signal wire to ground with connector unplugged: no continuity.
- 3
Inspect the connector
Check the thermostat connector for corrosion and coolant.
- 4
Measure the heater
Measure the heater resistance at the thermostat.
Multimeter: Typically about 10–20 Ω; 'OL' means the heater is open.
- 5
Check supply and control
Check the supply voltage and the control wire from the control unit.
- 6
Replace and bleed
Replace the thermostat (with housing if integrated), refill with the correct coolant and bleed the system.
Frequently asked questions
Can I keep driving with P0598?
Yes. The thermostat still opens mechanically. Watch the temperature on long climbs and towing.
How much does it cost to fix P0598?
Typical repair costs are 60 € – 500 €, depending on the cause and the vehicle. The most common fixes are: signal or control wire shorted to ground; missing 5 V reference or supply voltage; internal short in the map-controlled thermostat heater. Always confirm the cause with the tests above before buying parts.
Can I drive with a thermostat heater code?
Yes. The thermostat still opens at its mechanical temperature; only the electronic control is lost.
Can I replace only the heating element?
Usually not – it is built into the thermostat.
What is the difference between P0598 and similar codes?
P0598 belongs to a group of codes for the same component that differ in the type or location of the fault: P0597 – Thermostat Heater Control Circuit / Open; P0599 – Thermostat Heater Control Circuit High. The tests on this page apply to the whole group; the type of fault tells you where to start.
Related fault codes
This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.