Note: If a new electronic control unit (ECU) needs to be installed, this work should be entrusted to a Peugeot/Citroën dealer. After installing the new ECU, it must be initialized, which requires the use of specialized diagnostic equipment.
Models produced before September 2002.
25. The battery pack is located in a plastic box, which is part of the rear section of the battery shelf. On some engines the ECU mounting nuts/bolts are difficult to access and it is recommended to first remove the battery tray as described in chapter 5A, and then remove the control unit from the shelf on the workbench.
26. Disconnect the ground cable from the battery (see "Disconnecting the battery").
27. If applicable, remove the cover from the ECU, then lift the locking latches and disconnect the ECU electrical connectors (figure 13.27).
Figure 13.27. Lift the locking latches and disconnect the electrical connectors of the ignition control unit (early models)
28. Loosen the nuts or remove the bolts and remove the battery support plate from the battery shelf.
29. Loosen the nuts or remove the bolts and separate the ECU from the support plate.
30. Installation is carried out in the reverse order of removal. Connect the electrical connectors securely.
Models produced after September 2002.
31. The electronic control unit is located in the left rear corner of the engine compartment, above the upper support of the suspension strut.
32. Disconnect the ground cable from the battery (see "Disconnecting the battery").
33. Loosen the nuts and remove the ECU cover, if applicable (figure 13.33, a, b).
Figure 13.33, a. Unscrew the nuts (marked with arrows)...
Figure 13.33, b....and remove the cover of the control unit (later models)
34. Lift the ECU and remove it from the support bracket, then lift the locking latches and disconnect the electrical connectors (figure 13.34).
Figure 13.34. Remove the ECU from the support bracket and then disconnect the electrical connectors (later models)
35. If necessary, after unscrewing the three mounting nuts, you can remove the support bracket (figure 13.35).
Figure 13.35. Bolts for fastening the support bracket of the electronic control unit (marked with arrows) (later models)
36. Installation is carried out in the reverse order of removal. Connect the electrical connectors securely.
Information copied from the resource PeugeotBook