P0598 - THERMOSTAT HEATER CONTROL CIRCUIT LOW

The thermostat heater has the function of controlling the coolant flow, as well as regulating the engine temperature while the engine is running. The thermostat is supplied with 12 volts of power by the ECM (Engine Control Module).

When the engine thermostat system exhibits erratic operation, a series of fault codes can be set to indicate such a condition to the driver. In the case of the DTC P0598 OBDII code, it indicates that the voltage in the thermostat control circuit is well below the allowable voltage, causing unstable system operation.

• Check Engine light comes on.
• The temperature gauge indicates readings far in excess of those required for good engine performance.

The reasons for setting the P0598 OBD2 diagnostic code are:

• The thermostat electrical connector may be corroded or misadjusted.
• The radiator coolant may be leaking.
• Possibly the wiring connecting the ECM and thermostat have common damage.
• The thermostat may be faulty.

To properly troubleshoot the P0598 OBDII fault code you must consider the following:

• Check that the radiator coolant level is correct. Keep in mind that if the coolant level is too low, the thermostat will not work properly.
• Check that the thermostat connector is in good condition. If you discover high levels of corrosion that prevent the correct performance of the circuit, you should make the necessary adjustments.
• Measure the thermostat resistance based on the manufacturer's specifications. If adjustments to the thermostat are necessary, refer to the diagnostic steps given in the service manual.