Fix P0597: Mechanic’s solutions that WORKED

The P0597 OBD2 code indicates a malfunction within the thermostat heater control circuit, signaling an issue that prevents the engine’s thermostat from operating correctly. This code is particularly significant because the thermostat plays a crucial role in managing the engine’s temperature, ensuring it warms up quickly and maintains an optimal temperature for operation.

P0597 quick overview

Meaning	P0597: Thermostat Heater Control Circuit/Open
Is it serious?	Yes, it can lead to engine overheating and potential serious engine damage if not addressed.
Possible causes	– Faulty thermostat heater – Open or short in the thermostat heater circuit – Poor electrical connections – Faulty engine control module (ECM)
How to diagnose?	Check for battery voltage at the thermostat connector with the key on. Test thermostat resistance to be within the specified range (usually 14-16 ohms). Verify ground side control of the heater by the ECM. Inspect the circuit for poor connections, chafed harness, or plug defects. Replace the thermostat housing if the thermostat heater element tests open. Inspect metal tube for leaks or damage before replacing the thermostat housing. Confirm power to the element is battery positive and ground is supplied by ECM.

How to fix P0597 – learn from mechanics

I looked into P0597 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Ford

Vehicle information 2003 Ford Ranger XL 2.3L

Issue + repair history

• MIL lamp on
• Trouble code: P0597
• No previous repair history mentioned
• Mechanic suspected heating element in the thermostat housing

Other OBD2 Codes + Test Results

• OBD2 Code: P0597 – Thermostat heater control circuit
• Test Results: Thermostat housing removed, element tested open ohms

Mechanic suggestions

• Check for battery voltage at thermostat connector wire with key on
• Test thermostat resistance (14-16 ohms)
• Verify ground side control of heater by PCM
• Test circuit for poor connection due to chafed harness or plug defect
• Try replacing thermostat housing
• Check metal tube for leaks or damage before replacing thermostat housing
• Confirm power to the element is B+ and ground is supplied by ECM

Final fix Replacement of thermostat housing, as the element tested open ohms.

Case #2: Mini Cooper

Vehicle information 2007 Mini Cooper S 1.6L

Issue + repair history

• Cooling system issue
• Trouble code: P0597 – Thermostat Heater Control open or short
• No previous repair history mentioned
• Thermostat heater element tested open
• Replaced thermostat with OEM part and BMW coolant

Other OBD2 Codes + Test Results

• OBD2 Code: P0597 – Thermostat heater control open or short

Mechanic suggestions

• Replace the T-Map Thermostat
• Use OEM part for replacement
• Verify functionality of thermostat heater coil located inside the thermostat housing
• Ensure the temperature light did not come on, indicating an overheating issue

Final fix Replacement of thermostat with OEM part and BMW coolant. Thermostat heater element tested open, causing the trouble code. After replacement, codes are cleared.

Case #3: Audi

Vehicle information 2009 Audi S5 4.2L

Issue + repair history

• MIL lamp on
• Overheating issue after driving for a while
• Transmission goes into fail-safe mode, staying in low gear
• Trouble code: P0597 – MAP cooling thermostat open circuit
• Right engine mount solenoid valve short to B+
• Thermostat resistance tested at 3M ohms, confirming it was open
• Right side engine mount had spent all its fluids out
• No further repairs conducted due to customer’s financial constraints

Other OBD2 Codes + Test Results

• OBD2 Code: P0597 – MAP cooling thermostat open circuit
• OBD2 Code: P1575 – Right Engine Mount Solenoid Valve Short to B+
• Transmission scanned for codes, no faults found

Mechanic suggestions

• Scan the TCM for codes to address transmission issues
• Ensure the coolant is flowing and check for signs of leaks or a stuck thermostat
• Check if the transmission went into safe mode due to instructions from the engine PCM
• Consider driver behavior (left foot brake-right foot accel) affecting drive-by-wire systems and causing reduced power

Final fix

Repaired thermostat wiring

Diagnostic Step	Explanation
Check for battery voltage at the thermostat connector	Ensures power reaches the thermostat, necessary for its operation.
Test thermostat resistance	Confirms the thermostat’s electrical integrity; it should fall within a specific range.
Verify ground side control by ECM	Checks if the engine’s computer properly controls the thermostat’s ground connection.
Inspect circuit for poor connections	Looks for any wiring issues that could disrupt the thermostat’s function.
Replace thermostat housing if needed	A faulty thermostat housing can prevent proper thermostat operation.
Inspect metal tube for damage	Ensures the coolant flow is not obstructed, which is vital for engine temperature regulation.
Confirm power to the element	Verifies that the thermostat receives the correct power and ground for operation.

The P0597 code points to an issue with the thermostat’s heater control, which can affect your vehicle’s ability to regulate engine temperature properly. The detailed diagnostic steps and the final fixes from the service cases of a Ford Ranger, Mini Cooper, and Audi S5 emphasize the importance of thorough inspection and adherence to manufacturer specifications when addressing this code. Ignoring this problem could lead to more severe engine issues, emphasizing the need for prompt and accurate diagnosis and repair.