I know a few people found this thread interesting before the forum problems, so i thought i'd repost it. I'd posted the same stuff on the Saab forum so it was easily retrieved..!
Just though I’d share with you my experiences with regard to EGR’s DPF’s and tuning boxes, on my 2007 Saab 93 1.9TiD150 Auto. It’s quite long and detailed, but hopefully you’ll find it interesting..!
At the beginning of July I got a tuning box from ebay, with 8 settings. I read about others with the same box running on setting 8, so fitted mine on setting 7. Performance was impressive, but it went into limp mode after a couple of days. I connected up to my op-com and found a fault code relating to DPF saturation so I removed the tuning box, and forced a regeneration. (it ran at 3000rpm for about 10min, and dpf saturation figure went from 49% to 70%.. seemed odd way around but improved the fault)
All was fine for a week, so I refitted the tuning box, this time on setting 3 as recommended by the suppliers. It ran well for another few weeks, until on Friday when leaving work after travelling about 300 yards it completely lost power. It felt ok on tick-over, but revved in a very lumpy way between 1000 and 2000rpm. Once over 2000rpm it sounded and felt ok. I removed the tuning box but it stayed the same, so I put the gearbox over into manual to try and keep the revs up to get home. After about 5 miles the EML (engine management light) came on and went into limp mode. I limped home with the engine giving out less and less power, until it eventually stalled and wouldn’t restart, luckily about 20metres from my house! I pushed it the rest of the way, and left it there till the morning.
The next day I tried to start it, but it only ran for about 4 seconds before stalling again.
I plugged op-com in and found the fault code was p2279 Air intake leak detected, and looked this up on the net. A couple of posts on Vectra-C suggested it could be either the EGR or the DPF. The DPF saturation reading was 26%.
The removed EGR seemed to move about 2 or 3 mm when activated by op-com, but the test wasn’t conclusive as I wasn’t sure whether the valve needed assistance from exhaust pressure or manifold vacuum to operate.
I then removed the DPF, and found it looked pretty well blocked. I flushed it out using a gallon of unleaded, pouring it through backwards about 7 times (filtering the petrol through a sock between flushes). The first couple of flushes liquid flow was slow, but as it cleared the petrol was flowing through much faster by the end. I then poured 2 buckets of plain hot water through to clean the petrol out. It looked like new inside both ends by the time I’d finished, and the hot water was flying through. I left it to drain while I had a brew, and refitted it.
The engine started, and was great on tick-over, but wouldn’t rev.
I decided as a process of elimination to blank off the EGR to see if that had any effect, so a made a solid copy of the bottom gasket out of a coke can. The engine started, and revved freely. It felt sorted – Result..!
I took it for a drive and performance was superb, but fault codes relating to no EGR flow came up (no surprise there..) but after about 10 mins it went into limp mode with p1901-75 “DPF high differential pressure”.
I knew the DPF was like new inside, so with op-com I hit the “replace DPF” button, which reset the saturation to 0%, and the distance since regen to zero.
I removed and thoroughly cleaned the EGR, and activated it using op-com, this time getting about 8mm of travel. EGR refitted and blank removed, the engine felt like it had a bit less grunt, but the op-com readings for the EGR operation were stable and the “no EGR flow” fault stayed away.
Using the car yesterday, the EML comes on every 5 mins or so with p1901-75 “DPF high differential pressure”. I just hit “clear fault codes” and keep driving. I’ve been watching the DPF differential pressure readings, which sit around 10kpa at idle, around 40kpa steady acceleration, and upto 94kpa on full throttle.
I tried last night to force a DPF regeneration, which took the revs to 3k as expected, but the EML came on after about 2mins, the revs ramped down, and the little box popped up to say “regeneration completed”. But, the EML was on, and in limp mode. I reset the fault codes and drove it, but I’m still getting p1901-75 with the EML and limp mode.
DPF readings are now 14% saturation and 85km since regen.
This morning I tried disconnecting the two hoses going to the Differential pressure sensor (on the bulkhead, behind the EGR) and the car drove without the EML coming on, but with a fault code present relating to differential pressure connection problems.
So, my current thinking is to leave it a little longer with the 2 hoses disconnected from the differential pressure sensor, and have another try at forcing a regeneration at some point – either with or without the sensor, but maybe the regen process uses this pressure differential to decide when regen is complete?
Into the future I’d also like to blank off the EGR, or restrict it, or even allow it to draw in clean air via a pipe from the airbox (pre-maf of course), having noticed a definite improvement in performance with it blanked off.
I’m not sure if this was all caused by the tuning box, or if the EGR was sooted up and lazy in operation already, but I’ve learnt a lot about this EGR/DPF stuff this weekend..!
I hope some of you will find all this interesting, and I’d welcome any suggestions you may have for dealing with my current p1901-75 “DPF high differential pressure” fault.
Ok, Time for a quick update..
It turned out that I’d only partially unblocked the DPF, which explained my “DPF high differential pressure” faults.
The readings were peaking at 96kpa, and sitting around 20kps at tickover.
I fitted a miniature pressure regulator, to cap the High pressure pipe at 20kpa, in order to drive the car without the fault light coming on.
The saturation value rose steadily with mileage  and once it reached 600km and 90% saturation, a regeneration took place automatically. 
After the regen, the differential pressure dropped to virtually zero on tickover and peaks at 9 or 10kpa.
So, it fixed itself in the end..!
 From reading the Saab Workshop Information CD, the saturation figure is purely a guess! The engine knows how far and how hard you’ve driven, and does a regen when it thinks it needs it (this is why I think the tuning box was to blame here – it tricks the engine into burning more fuel than it thinks). The differential pressure sensor does not give the saturation figure, it’s only there to throw up a fault code when the dpf gets badly blocked.
The DPF is a ceramic block, which is essentially a load of porous tubes, alternately blocked off front and back. The exhaust gasses must pass through the walls of these tubes, which catch the soot. The soot is then combusted in a Regeneration process which heats the ceramic block to 600 deg C by injecting a little extra fuel into the engine on an exhaust stroke which then combusts in the exhaust to raise the temperature. Regens take place approximately every 600km, depending on your driving style.
 the regen took place while I was sitting in a traffic queue at temporary lights (i.e. on tickover, not at high revs..!). I had the laptop on the passenger seat, and noticed the “regen % complete” value slowly climbing. I checked the exhaust temp and it was just over 600 deg C. I wouldn’t have noticed it without the laptop plugged in.