Code Definition

B1590 — Autolamp Delay Increase Circuit Short To Ground

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

About B1590

B1590 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 B1590 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.

B1590 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 the autolamp delay increase signal wire from the headlamp switch potentiometer used to set how long the headlamps remain on after key off. DTC B1590 sets when the BCM detects that the autolamp delay increase circuit is shorted to ground, meaning the input voltage is being pulled to zero or near zero outside its expected operating range. This is most commonly caused by a chafed wire contacting bare metal, a failed switch internally shorted to its own ground reference, or moisture and ...

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