Ever since the release of Saab's Trionic engine management system in the early '90s Saab has been know for its innovative computer-powered Engine Control Unit (ECU). Saab uses a similar Trionic 5 system in its baseline 9-5 and Trionic 7 in its flag ship 9-5 Aero model.
What many people don't know is that these ECUs come from the factory programmed for "the average Joe." Once you know where to locate the ECU, driving enthusiasts can swap out or reprogram these computers with a few simple tools to see gains in horsepower, torque, and fuel efficiency.
Set the hand break, remove the key from the ignition switch, and open the bonnet.
Disconnect the negative battery lead from the battery terminal using the adjustable wrench. Usually this lead is black. This will prevent any possibility of shock or shorting during the project.
Clear away any debris that has collected in the plastic run-off cover located at the bottom of your windshield.
Remove the screws that hold the plastic run-off cover and rubber seal in place with the Phillips head screwdriver.
Lift up the plastic run off cover. It does not have to be completely removed. This saves you from needing to remove the windshield wipers and is usually enough space to access the ECU. This will expose the ECU protective cover, which is oval shaped and has a hose containing wires running from it.
Loosen and remove the 10-mm nuts holding the plastic protective cover in place with the 10-mm socket wrench and extender. Lift up the plastic protective casing to expose the ECU and wiring.
You have now located the ECU. To remove the ECU, lift the black handle to disconnect the wiring connector, undo the two 10-mm nuts on either side and lift out the silver box.
Follow these steps in reverse order to replace the ECU and plastic covering.
These instructions are for the 2003 SAAB 9-5 ECU. The interface for the 2003 SAAB 9-3 ECU is located under the dash board. Tampering with a 2003 9-3 ECU is not advised and should only be altered with software, not hardware.
Disconnecting the ECU will cause the computer to reset. Although the effects are usually hard to notice, the car may not "feel" the same the first few times you drive it. This is the computer trying to relearn the most efficient fuel combination and should go away on its own within two to three days of driving.