Code Definition

B1259 — Solar Radiation Sensor Circuit Open

System: Body  |  Type: Manufacturer-Specific  |  Make: Generic

About B1259

B1259 is a manufacturer-specific body diagnostic trouble code. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B1259 is stored, the module has detected an open (broken or disconnected) electrical path in the monitored circuit; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: Body (B) codes are often stored in the body control module, airbag module, or climate module. A basic OBD-II tool usually will not read body codes — an enhanced or OEM-level scan tool is typically required.

B1259 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The climate control module monitors the solar radiation (sunload) sensor signal as part of the automatic HVAC strategy, using cabin sunlight intensity to adjust blower speed, mode door position, and target discharge temperature. DTC B1259 sets specifically when the module detects an open in the sunload sensor circuit, where signal voltage sits at the upper rail with no measurable load, indicating the sensor or its wiring has lost circuit continuity. The sunload sensor is typically a photodiode in the upper dash near the windscreen, fed a low reference voltage from the climate module and return...

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