What Does P0598 Mean?
The thermostat heater control circuit is reporting a low voltage condition. The PCM detects that the heater control line is being pulled to ground when it should not be, or the circuit is drawing excessive current. This may cause the thermostat heater to be energized constantly or may blow the protective fuse. The thermostat will still function mechanically but without PCM-controlled heating.
Common Causes
35%
Short to ground in the thermostat heater control wire, often due to heat damage near the engine
25%
Thermostat heater element with internal short to housing (ground)
20%
Coolant contamination in the thermostat heater connector creating a conductive path
12%
Damaged wiring insulation from engine heat exposure near the thermostat housing
8%
PCM internal driver shorted low
Diagnostic Steps
1
Disconnect the thermostat heater connector and check if the low circuit condition clears — if the PCM no longer sees a low signal, the fault is in the thermostat or its pigtail.
2
Measure the thermostat heater resistance — typical is 10-30 ohms; a near-zero reading indicates an internal short to the housing ground.
3
With the heater disconnected, check the control wire for resistance to engine ground — it should read OL; any low resistance indicates a harness short.
4
Inspect the thermostat connector area for coolant leaks — antifreeze is conductive and can create shorts between the heater terminals and the grounded thermostat housing.
5
Check the wire routing near the exhaust manifold and thermostat housing — heat can melt insulation and cause shorts to the engine block.
Estimated Repair Cost
$150 - $500
Parts + labor, varies by vehicle and location
The thermostat heater control circuit is reporting a low voltage condition. The PCM detects that the heater control line is being pulled to ground when it should not be, or the circuit is drawing excessive current. This may cause the thermostat heater to be energized constantly or may blow the prote...
The most common cause of P0598 (Thermostat Heater Control Circuit Low) is: Short to ground in the thermostat heater control wire, often due to heat damage near the engine
Typical repair costs for P0598 range from $150 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. The thermostat continues to function mechanically. If the heater is constantly energized, the thermostat may open slightly earlier than normal, causing a minor decrease in fuel economy and a slightly cooler operating temperature. No risk of overheating or engine damage.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0598 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Cooling System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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