Diagnostic article Generic OBD-II
P0597: Thermostat heater open-circuit classification uses driver status
P0597 identifies an open thermostat-heater control circuit through monitored output-driver status.
Read before applying this article
Documented application
2009 General Motors diagnostic parameter file 09OBDG01 GMDAT Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P0597 concerns the electrically heated thermostat's control circuit in this GM GMDAT example. The controller monitors the heater output driver and uses its diagnostic status to classify an open circuit. This is not the same as proving that the thermostat is mechanically stuck open.
Similar voltage observations can have different classifications
The table describes low voltage while the driver is open as evidence that can relate to either an open circuit or a ground short. The output driver's status information separates the P0597 open-circuit classification from the neighboring P0598 ground-short classification. A voltage reading without the driver state and status can therefore be misleading.
The monitor operates with the engine not cranking, the run/crank state active and ignition within the required range. It also depends on a determinate result from the relevant preceding circuit check. These are reasons to distinguish an incomplete test from a passing one.
Verify the electrical repair before judging warm-up
The published evaluation uses 15 failures in 30 one-second samples. Preserve the command and fault-status evidence rather than using coolant warm-up alone to judge this electrical code.
Use the vehicle's heater-circuit procedure to identify the actual break or faulty element. The summary supplies no automatic thermostat replacement decision. Verification should include completed circuit monitoring; any separate temperature-performance complaint needs its own assessment after the electrical signal is credible.
Source and applicability
2009 General Motors diagnostic parameter file 09OBDG01 GMDAT Engine Diagnostics.pdf. Section-specific modules and calibrations; no per-code model or engine applicability established. This explanation describes the documented monitor, not a universal repair procedure.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Thermostat Heater Control Circuit/Open
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT