1997-1998 Saab 900 Body Electronics: A Guide to the TWICE & Central Locking Modules

Understanding the "Body Control Module" in a 1997-1998 Saab 900

If you're searching for a single Body Control Module (BCM) for a 1997-1998 Saab 900, you won't find one. Saab engineered this generation (often called the NG900) with a distributed electronics system. Instead of one central computer for body functions, there are several dedicated modules. The two most commonly confused and critical modules are:

• TWICE Module: The security and immobilizer computer. This is the most complex module and has strict programming requirements.
• Central Locking Control Module: The relay module that directly powers the door locks. This is a much simpler component.

This guide will cover both modules, as their symptoms can sometimes overlap, but their replacement procedures are vastly different.

The TWICE Module: Security, Keys, and Starting

The TWICE (Theft Warning Integrated Central Electronics) module is the most critical body-related computer in your Saab. It is responsible for recognizing your key's transponder chip to allow the engine to start. It also controls the alarm system and receives signals from your key fob remote to lock and unlock the doors.

Symptoms of a Failing TWICE Module

• "KEY NOT ACCEPTED" Message: The Saab Information Display (SID) shows this message, and the car will not crank or start.
• No-Crank, No-Start: You turn the key, the dash lights come on, but the starter motor does not engage.
• Remote Key Fobs Don't Work: The doors will not lock or unlock using the remote buttons, but may 🎬 Learn how to change the battery in your Saab key fob. still work with the key in the door.
• Flashing Security Light: A persistent or flashing security light on the dashboard is a common indicator of a TWICE module or key communication problem.
• Water Damage: The TWICE module is located under the driver's seat beneath the carpet and is highly susceptible to water damage from clogged sunroof drains or window seal leaks. If you experience strange electrical issues after heavy rain, this module should be your first suspect.

Programming: A Saab Tech 2 is Required

This is the single most important factor when dealing with a TWICE module. You cannot simply swap a used TWICE module from another car. The TWICE module is electronically "married" to the car's main Engine Control Unit (ECU).

• Installation: To install a new or used TWICE module, a technician must use a Saab-specific Tech 2 scan tool to perform a "Spare Part Programming" procedure, which marries the replacement module to your car.
• Keys: All keys, including spares, must be present during the programming session. Any keys not programmed at that time will be permanently locked out and rendered useless for that vehicle.
• Dealer or Specialist Required: This programming can only be done by a Saab-specialized independent mechanic or a former dealer with the proper Tech 2 tool and software. Most general repair shops cannot perform this task.

The Central Locking Control Module

This module is much simpler than the TWICE unit. It is essentially a box of relays that sends power to the door lock actuators. It takes commands from the TWICE module (when you use the remote) or the door lock switches and does 🎬 See how to remove the door lock assembly and handle. the heavy lifting of locking and unlocking the doors.

Symptoms of a Failing Central Locking Module

• All Power Locks Fail Simultaneously: None of the doors lock or unlock with the remote or the interior switch.
• Intermittent Lock Operation: The locks work sometimes but not others, often influenced by temperature or bumps in the road. This often points to failing solder joints inside the module.
• Locks Actuate on Their Own: The doors may lock and unlock randomly while driving or when the car is parked.
• Audible Clicking from the Module: You may hear a clicking sound from the module's location when you press the lock/unlock button, but the locks don't move. This indicates the relays are trying to work but are failing to make contact.

Programming & Installation

Unlike the TWICE module, the Central Locking Control Module is a simple plug-and-play part. No programming is required. Simply disconnect the battery, swap the module, and reconnect the battery.

Module Locations

• TWICE Module: Located under the driver's side (LHD) front seat, beneath the carpet and a ventilation duct. You will need to unbolt and tilt the seat back to access it.
🎬 Watch this video for a walkthrough on removing the TWICE module.
• Central Locking Module (3-Door/5-Door Hatchback): Located in the passenger-side footwell, on the side wall near the front door hinge, often tucked below other control modules.
• Central Locking Module (Convertible): Located in the trunk, behind the left-side trim panel near the wheel housing.

Buying a Used Body, TWICE, or Locking Module

Buying a used electronic module for your Saab 900 can be a smart way to save money, but it carries significant risks if you don't know what to look for.

Buying a Used TWICE Module (High Risk)

• Match Part Numbers Exactly: There are different versions of the TWICE module. You must match the part number from your original module exactly.
• Inspect for Water Damage: Ask the seller for clear pictures of the case and connectors. Look for any signs of corrosion or water stains, as this is a common failure point.
• Consider a Cloning Service: Some companies offer a service where you send them your original (faulty) TWICE module and a compatible used replacement. They will clone the data from your old module to the new one, making it plug-and-play and avoiding the need for a Tech 2.

Buying a Used Central Locking Module (Low Risk)

• Verify Compatibility: Ensure the module came from a 1994-1998 Saab 900. Part number 4710257 is a common part for these models.
• Physical Inspection: Check the connectors for any bent or corroded pins.
• Plug-and-Play: Because no programming is needed, this is a much safer used part to purchase.

Cost Comparison

Prices can vary significantly based on availability and condition. Programming labor is a major factor for the TWICE module.

Frequently Asked Questions (FAQ)