● Powertrain Control Module (PCM) — Manages engine functions such as spark timing,
fuel mixture, throttle position, variable valve timing, engine cooling, charging system output, exhaust gas recirculation (EGR) and other emission functions, also onboard diagnostic (OBD II) fault detection.

● Transmission Control Module (TCM) — If not integrated into the PCM, it controls the operation of the automatic transmission.

● Body Control Module (BCM) — Handles climate control functions, onboard communications, entertainment and navigation systems, and often serves as the gateway to the controller area network (CAN) communications bus that links all of the other modules together.

● Antilock Brake/Stability Control module (ABS) — Oversees the operation of the antilock brakes, traction control and stability control systems.

● Airbag control module — Monitors the crash sensors and deploys the air bags in the event of a collision.

● Electronic steering control module — Operates the power steering system on vehicles with electronic steering.

● General Electronic Module (GEM) — Functions may include interior lighting, door/seat belt warning lights, horn, etc.

● Front and rear lighting modules — Operates the headlights, tail lights, turn signals, backup lights, marker lights and flashers.

● Instrument cluster module — Controls the instrument cluster gauges and dash warning lights.

● Fuel pump control module — Turns the fuel pump on and off, and provides variable speed operation in some applications.

● Keyless entry module — Detects signals from a keyless entry fob to unlock doors and/or a smart key to make the engine ready for starting (or remote starting). May also communicate with the Tire Pressure Monitor System (TPMS) module to relay tire pressure information from the individual tire pressure sensors to the TPMS module.

● Tire Pressure Monitor Module (TPMS) — Detects low tire pressure and alerts driver when tire pressure drops suddenly or below minimum acceptable pressure.

● Power seat, power window, power lock, power door/liftgate modules — Control their respective system functions.

Electronic modules have no moving parts, but they do age over time and may fail at any time for a variety of reasons. Heat, vibration, moisture contamination, corrosion and voltage overloads can all cause module failures. Flood-damaged vehicles usually are totaled by insurance companies because they know what water damage can do to electronics and wiring connections.

PCMs are covered by an 8-year/80,000-mile federal emissions warranty, but most other modules are only covered under a new vehicle’s basic warranty (typically 3 years/36,000 miles). Once a vehicle is out of warranty most modules are not covered.

The aftermarket has expanded its module coverage significantly in recent years to keep pace with the proliferation of modules. Still, some modules may only be available from a new car dealer. But if an aftermarket replacement module is available for a customer’s application, there’s no need to send them back to the dealer. What’s more, most “remanufactured” modules cost much less than a new module. Some modules require reprogramming when they are installed, or must undergo a special relearn procedure before they will function normally.