P0597 on Cadillac
Thermostat Heater Control Circuit Open
P0597 on Cadillac vehicles indicates thermostat heater control circuit open. Au7o has documented this code across 1 Cadillac model — most commonly on XT5. P0597 is a cooling-system code indicating an open electrical circuit in the control for the heated (electronically controlled) engine thermostat. Many modern engines use a thermostat with a built-in heater element that the computer can energize to open the thermostat sooner for better temperature management and emissions. When the PCM commands that heater but detects no electrical continuity (an open circuit), it sets this code. It generally means the thermostat heater isn't being controlled, which can affect coolant temperature regulation, fuel economy, and emissions. Typical repair costs on Cadillac range from $250 to $650, depending on the specific model and root cause.
Common Causes of P0597
- •Failed thermostat heater element or integrated control thermostat
- •Open or broken wiring to the thermostat heater circuit
- •Corroded, loose, or disconnected thermostat connector
- •Blown fuse or open in the heater power feed
- •Poor ground or control-circuit fault from the PCM
- •Damaged PCM driver for the heater (rare)
P0597 on Cadillac by Model
Cadillac XT5(1 issue)
- Engine Thermostat Sticks Open on the 3.6L LGX - Triggers P0128, 'Steering Assist is Reduced' Message and A/C Shutdown2017-2020
The engine thermostat on the 3.6L LGX V6 commonly sticks in the open position, so the engine never reaches its target operating temperature. The ECM sets P0128 and, because the electric power steering assist and A/C compressor operation are both load-managed off engine/coolant state, the driver gets a 'Steering Assist is Reduced - Drive With Care' message and loses A/C, sometimes with noticeably heavier steering effort. Owners across 2017-2019 report this as the single most-repeated XT5 fault in NHTSA filings, often with the replacement thermostat housing on national backorder. It is a cooling-system fault masquerading as a steering and HVAC fault, which is why many owners are first quoted power-steering diagnostics.
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What does P0597 mean on Cadillac?▼
P0597 stands for "Thermostat Heater Control Circuit Open." P0597 is a cooling-system code indicating an open electrical circuit in the control for the heated (electronically controlled) engine thermostat. Many modern engines use a thermostat with a built-in heater element that the computer can energize to open the thermostat sooner for better temperature management and emissions. When the PCM commands that heater but detects no electrical continuity (an open circuit), it sets this code. It generally means the thermostat heater isn't being controlled, which can affect coolant temperature regulation, fuel economy, and emissions. On Cadillac specifically, this code is documented across 1 model.
What causes P0597 on Cadillac vehicles?▼
Common causes on Cadillac: Failed thermostat heater element or integrated control thermostat, Open or broken wiring to the thermostat heater circuit, Corroded, loose, or disconnected thermostat connector, Blown fuse or open in the heater power feed, Poor ground or control-circuit fault from the PCM. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0597 on a Cadillac?▼
Repair costs on Cadillac range from $250 to $650, depending on the specific model and root cause.
Which Cadillac models have P0597 documented?▼
Au7o has documented P0597 on 1 Cadillac model: XT5.