Code Definition

B1591 — Autolamp Delay Decrease Circuit Failure

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

About B1591

B1591 is a manufacturer-specific body diagnostic trouble code recorded for Ford vehicles. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B1591 is stored, the module has detected an electrical-circuit fault in the wiring, connector, or driver associated with the named component.

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.

B1591 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) on Ford, Lincoln, and Mercury vehicles equipped with the Autolamp system monitors a separate decrease input from the headlamp switch potentiometer that allows the driver to shorten the autolamp delay time. DTC B1591 sets when the BCM detects a generic circuit failure on the autolamp delay decrease input that does not match a specific open, short to battery, or short to ground pattern. The decrease circuit is essentially the mirror of the increase circuit and shares the same connector and harness path. With this code present the autolamp delay function may not resp...

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