While retro-fitting the CDL lever to 1999-2002MY Discovery 2's is a popular upgrade, it's often followed up with a modification that prevents the SLABS ECU from detecting the CDL has been locked. On the 1999-2002MY D2's the locked CDL triggers a mode of operation that disables Traction Control and reduces the effectiveness of ABS, EBD and HDC. By cutting the wire from the CDL switch the SLABS ECU operates as if the CDL is unlocked regardless of its actual state.
The 2003 and 2004MY D2's offered the CDL lever as a factory option, and this was fitted to all vehicles imported into Australia. As part of this change Land Rover revised the programming of the SLABS ECU to work correctly with the locked CDL. While it is difficult to quantify the revised ECU is claimed to have improved ABS and ETC programming, and I noticed what appeared to be slight improvement in pedal feel after upgrading the ECU in my vehicle.
The main benefit of upgrading to the later ECU is that with the CDL locked the SLABS programming is altered to work in conjunction with the changed power transmission.
There were two variants of the update ECU produced;
SRD000150 which was fitted to 2003MY vehicles
SRD500070 which was originally fitted to 2004MY vehicles
Vehicles built prior to 2003MY should be fitted with a SRD000070, as the ECU revisions prior to this were subject to a recall which mandated installation of the SRD000070 ECU.
The recall - A/B/D 263 issued in 2002 - indicates that metallic debris within the hub can attach to the wheel speed sensor causing the sensor to misread speed, which results in the SLABS unit incorrectly reducing braking pressure. The VINs covered by the recall were fitted with SRD100461 or SRD100462 from the factory. If these are still fitted the vehicle has missed the recall.
Many Ebay wreckers list these earlier revisions for sale - be warned and steer well clear. It also pays to check with the vendor precisely what they will send out. A friend recently bid on a listing for a SRD500070 and was sent an ECU that had been subject of the safety recall. The seller came through, but it underlines the importance of checking!!