21 is pretty normal for me. Under certain driving conditions (i.e. cold start with STM=21 or slow traffic) I have seen up to 26 grams.
32 is the limit for auto regen, you need a manual/service regen. No CEL or "Keep Driving Message"? If you continue to drive you could trash the dpf. You can go to the dealer OR if you have an android smart phone, elm327 or bluetooth obd2 device and torque pro app, you can buy Biscan as an add-on for TrqP and force a regen yourself. Snipesy can help with that, he made the app.
When my charge pipe came off and I drove, i accumulated 93 grams and got dpf full and immentient shut down in the DIC. I believe eventually my dpf was replaced, I'd have to check paperwork.
From GM SI: Engine/Propulsion / Engine Controls and Fuel - 2.0 LUZ Diesel / Description and Operation / Exhaust Aftertreatment System Description
Normal DPF Regeneration Over time, the soot trapped on the cell walls acts to restrict exhaust flow through the DPF reducing its effectiveness as well as reducing engine efficiency. This restriction in exhaust flow produces a pressure drop across the DPF that increases as the once porous cell walls become saturated with trapped soot. A DPS monitors the pressure drop across the DPF and provides the ECM with a voltage signal proportional to soot buildup. Once soot buildup reaches a specified limit, (usually around 22 - 25 grams) as signaled by the increased pressure drop across the DPF, the ECM commands a regeneration event to burn-off the collected soot during normal vehicle operation. Regeneration events occurring during vehicle operation are known as normal regenerations as they occur automatically and without driver knowledge. In general, the vehicle will need to be operating continuously at speeds above 48 km/h (30 mph) for approximately 20–30 minutes for a full and effective regeneration to complete. The frequency of normal DPF regeneration is a function of the engine run time, miles driven, and fuel consumed since the last regeneration event. Under normal operating conditions, the normal DPF regeneration is initiated after approximately 85 gallons of fuel used or a maximum distance traveled of 2009 km (1250 miles.) To initiate a normal DPF regeneration event, the ECM commands additional fuel via post-injection in order to create the additional exhaust heat in the DOC necessary to promote regeneration and burn-off the collected soot. During regeneration exhaust temperatures may exceed 550°C (1,022°F) due to the rapid catalytic combustion of soot within the DPF. Conversely, under low engine speed or light loads, exhaust temperatures may be too low to promote proper regeneration. To protect the DPF catalyst from thermal damage due to excessive soot combustion or from sulfate poisoning at low temperatures, the ECM monitors EGT sensors upstream and downstream of the DPF during regeneration. If the vehicle is slowed to idle speed during a normal DPF regeneration, the engine may maintain an elevated idle of 800 RPM until the DPF is cooled to a calibrated temperature. Should the EGT sensors indicate that regeneration temperatures have exceeded a calibrated threshold, regeneration will be temporally suspended until the sensors return to a normal temperature. If regeneration temperatures fall below a calibrated threshold, regeneration is terminated and a corresponding DTC is set in the ECM. Under most conditions, the soot collected within the DPF burns off during normal regeneration cycles. Periodic regeneration prevents the buildup of soot from reaching a level where its burn-off could produce damaging high temperatures within the DPF. Vehicles operated at prolonged low speed or low loads where normal regeneration does not occur will eventually reach a high soot load condition. When the increased pressure drop across the DPF is detected by the DPS, the ECM illuminates the DPF lamp in the instrument cluster and sends a Clean Exhaust Filter message to the driver information center (DIC). The owner manual diesel supplement describes how the vehicle should be driven in order to enable normal regeneration.
And according to SI, DPF soot levels of 32g that are seen by the ECM for greater than 30 seconds sets DTC code P2463 Diesel Particulate Filter (DPF) Soot Accumulation. At this point the car requires a service regen. This usually happens after driving the car with the Clean Exhaust Filter message and not allowing it to regen, but the it could also happen before it gets to that point.