Code Definition

B1556 — Ignition Run/Start Circuit Open

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

About B1556

B1556 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 B1556 is stored, the module has detected an open (broken or disconnected) electrical path 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.

B1556 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 B1556 code is set by the Body Control Module (BCM) when it detects an open circuit on the ignition run/start signal input. The ignition run/start circuit carries the run and crank signals from the ignition switch through to the BCM and other modules that depend on knowing the ignition state. An open is identified when the BCM expects to see battery voltage at its input but instead reads zero or near zero volts during the relevant key position. When this code is set, the vehicle typically presents with a no crank or no start condition, intermittent stalling, or accessory features that fail ...

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