P2B59: an open motor circuit at the coolant flow valve

P2B59 is the open-circuit member of the documented coolant flow valve motor diagnostics. The strategy checks whether either DC motor wire is disconnected. Its hardware-provided classification corresponds to load resistance above 200 kilohms.

An open-load report needs a valid hardware result

The diagnostic only evaluates an error indication that is not indeterminate. That qualifier matters: an unavailable hardware result is not interchangeable with a confirmed disconnected load. The row also requires the test enabled, powertrain relay voltage above 11 volts, the engine out of cranking and the diagnostic system active.

Confirmation uses 80 failed samples out of 100 at a 12.5-millisecond sampling interval. This provides persistence qualification; a single unexplained scan-tool reading does not describe the complete monitor decision.

How the code guides investigation

The specific next question is where the motor's electrical load becomes interrupted. Identify the exact valve circuit and use its service procedure to distinguish an unplugged connection, harness interruption and an open load within the assembly. The 200-kilohm monitor criterion is not an instruction to measure resistance through a powered controller.

Compare electrical evidence with valve feedback carefully. A valve that stays at one position can be the consequence of the open motor circuit, but position alone cannot identify the interruption. Verification should demonstrate a determinate, passing load diagnosis with the driver powered under valid conditions. Watching engine temperature settle normally does not prove that the motor circuit is now electrically intact.

Source and applicability

Documented 2025 GM gm-2025-04b monitor only; vehicle, engine and controller applicability must be established separately. GM monitor table, PDF page 851.