FAQ
TL;DR: Owner saw 9–10 L/100 km despite 5.5–6.5 shown; "reason for such combustion was clogged DPF." Fixing DPF restored consumption and stopped oil dilution on a Passat B6 2.0 TDI CBAB. [Elektroda, karl-88, post #17387236]
Why it matters: For Passat B6 2.0 TDI CBAB owners with high fuel use and rising oil, this FAQ shows what to check first.
Quick Facts
- Case data: 5.5–6.5 L/100 km indicated vs ~9–10 L/100 km actual on CBAB. [Elektroda, karl-88, post #17324686]
- Oil level rose ~4 mm in 800 km, indicating fuel dilution risk. [Elektroda, karl-88, post #17333384]
- Compression test OK; scan showed about 420 Nm torque, suggesting possible tune. [Elektroda, karl-88, post #17335524]
- Final fix: clogged DPF; after removal, consumption matched display and oil-in-oil stopped. [Elektroda, karl-88, post #17387236]
- Overfuel can also come from injectors with worn nozzles or broken springs. [Elektroda, cooltygrysek, post #17358484]
Why does my Passat B6 2.0 TDI CBAB show normal consumption on the computer but use much more fuel?
A clogged DPF can trigger frequent post-injections and higher backpressure, raising real fuel use. In this case, addressing the DPF brought indicated and actual consumption back in line and stopped oil dilution. Check DPF status and regeneration behavior before chasing other causes. [Elektroda, karl-88, post #17387236]
Can a clogged DPF raise my oil level?
Yes. Extra post-injection during regens can wash fuel past rings, diluting oil and raising the dipstick level. “Oil for immediate change because it is diluted.” Change oil, then resolve the underlying cause to protect the engine. [Elektroda, cooltygrysek, post #17335347]
My scan shows the DPF is only a few percent “full.” Could it still be restricted?
Yes. Percentage readings can mislead due to driving style, idling, and fuel quality effects. Ash accumulation or uneven soot loading can still restrict flow. “Depends on driving style and fuel quality.” Consider backpressure testing or professional inspection if symptoms persist. [Elektroda, cooltygrysek, post #17332813]
Can injectors overfuel even if the scan tool says they’re OK?
Yes. Balance or correction values can look normal while injectors mechanically overfuel. Worn nozzles or broken springs can cause this and increase consumption. “Either developed atomizer nozzles or broken springs.” Have injectors bench-tested or regenerated if suspected. [Elektroda, cooltygrysek, post #17358484]
Could a fuel leak be causing my high consumption?
Yes. Inspect lines, connections, and components for wetness or diesel odor. “Logic suggests that fuel is escaping (leaking).” On some variants, leaks occur at the fuel cooler; check if your car has one fitted. [Elektroda, decybel91, post #17324805]
What mass air flow (MAF) values should I compare?
Use a scan tool to compare specified versus actual air mass at set RPM and load. Don’t accept vague “it’s fine.” “Expected and delivered air mass.” Log both channels during a controlled road test to spot airflow issues. [Elektroda, iron64, post #17332537]
How can I check if a chip tune is installed?
Read ECU software identification and version with a scan tool. Non-stock maps often show altered software data. “It should display relevant software data on the computer.” Some tools can also compare checksums or read the flash. [Elektroda, cooltygrysek, post #17358484]
Can a tune alone explain high consumption and rising oil level?
Not necessarily. In this thread, the issue was a clogged DPF, not software. After fixing the DPF, consumption matched the display and oil stopped rising. Address hardware restrictions before blaming calibration. [Elektroda, karl-88, post #17387236]
How do I quickly triage high fuel consumption on a CBAB?
Try this: 1) Check crankcase blow-by at the breather and watch for rising oil. 2) Perform a compression test to assess rings and pistons. 3) Evaluate DPF health beyond a percentage; consider how city driving skews readings. “Another and basic diagnosis is checking compression.” [Elektroda, cooltygrysek, post #17332813]
What should I do if my oil level rises on the dipstick?
Stop extended driving and change oil immediately to protect bearings and turbo. “Oil for immediate change because it is diluted.” Then diagnose causes like DPF-related regens or injector overfueling to prevent recurrence. [Elektroda, cooltygrysek, post #17335347]
Does the CBAB common-rail have a fuel cooler that can leak?
Some cars lack a fuel cooler in this configuration. The OP’s CBAB had none fitted. Confirm your vehicle’s parts layout by VIN or catalog before hunting cooler leaks. [Elektroda, karl-88, post #17324908]
How can I tell if rings or pistons are damaged versus valve seals?
Check blow-by from the crankcase vent to assess ring sealing, then confirm with a compression test. Excess blow-by suggests ring or piston issues, but leaking valve seals can mimic symptoms. An experienced mechanic can judge by results. [Elektroda, cooltygrysek, post #17332813]
How much did the oil level rise in this case?
About 4 mm over 800 km. That’s a clear warning of fuel dilution during the fault window. Use it as a benchmark to recognize similar symptoms early. [Elektroda, karl-88, post #17333384]
What was the final fix and outcome in this thread?
The DPF was clogged and then removed. Afterward, real consumption matched the computer display, and fuel no longer entered the oil. The owner confirmed normal operation. [Elektroda, karl-88, post #17387236]
