Code Definition

B0004 — PCM discrete input speed signal missing

System: Body  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About B0004

B0004 is a generic (obd-ii standard) body diagnostic trouble code. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

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.

Because B0004 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The Powertrain Control Module (PCM) expects a discrete vehicle speed input, a switched or pulsed signal that changes state with road speed, usually sourced from the vehicle speed sensor (VSS) or the transmission output shaft speed sensor. DTC B0004 sets when the PCM receives no usable speed signal on this discrete input while other operating conditions indicate the vehicle should be moving. The PCM depends on this input for shift scheduling, torque converter clutch control, cruise control, speed limiting, and load calculations, so losing it can affect several systems at once. When the signal i...

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