I have the same engine, and its exactly the same GM engine as the Saab 9-3 1.9 Tid I used to have.
Saab were clear to point out that all oils that go in must have GM-LL-B-025 approval.
I make sure all the oil I use has ACEA B4 (as the manual states) along with GM-LL-B-025.
I've used Mobil 1 Turbo Diesel 0W-40 and have Mobil Super 3000 5W-40 in there at the moment. Both are fully synthetic.
Both these oils meet both specs.
Here's some info on the ACEA specs from Oils explained - what's written on your oil bottle, and what does it mean?.
A1 Fuel economy petrol
A2 Standard performance level (now obsolete)
A3 High performance and/or extended drain
A4 Reserved for future use in certain direct injection engines
A5 Combines A1 fuel economy with A3 performance
B1 Fuel economy diesel
B2 Standard performance level (now obsolete)
B3 High performance and/or extended drain
B4 For direct injection car diesel engines
B5 Combines B1 fuel economy with B3/B4 performance
C1-04 Petrol and Light duty Diesel engines, based on A5/B5-04 low SAPS, two way catalyst compatible.
C2-04 Petrol and light duty Diesel engines, based on A5/B5-04 mid SAPS, two way catalyst compatible.
C3-04 Petrol and light duty Diesel engines, based on A5/B5-04 mid SAPS, two way catalyst compatible, Higher performance levels due to higher HTHS.
I believe, the "HTHS" stands for High Temperature High Shear.
Do our engines need this? Is C3 specified in the handbook???!!!
Just found this on the Opie Oils website;
"ACEA C3 engine oils are suitable for diesel engines fitted with diesel particulate filters (DPFs). Very similar to C2 but without fuel-economy requirements. Frequently matches specifications for BMW and DaimlerChrysler diesel cars. ACEA C3 oils may be unsuitable for use in some engines. Consult your owners manual or use our online oil service pack recommendation if in doubt".
...which seems to imply C3 is all about DPF compatability, not performance level.