Code Definition

B1851 — Climate Control Temperature Differential Circuit Short To Battery

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

About B1851

B1851 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 B1851 is stored, the module has detected a short-circuit (voltage pulled to ground or to supply) in the monitored circuit.

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.

B1851 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 Body Control Module (BCM), or on some applications the Electronic Automatic Temperature Control (EATC) module, monitors the climate control temperature differential feedback signal to track blend door position and actual cabin air temperature versus the commanded set point. DTC B1851 is set when the temperature differential signal circuit is shorted to battery voltage, causing the module to see a signal voltage well above the normal operating range (typically near 12V instead of the expected 0V to 5V). The feedback circuit normally uses a potentiometer or thermistor fed by a 5V reference, ...

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