Item — HN Reader

I recently shopped for a 5 door hatchback. There are VW TDI's all over Utah. My understanding, from sales people, is that VW bought many of them back, "fixed" them, and put them back on the used market.

Can anyone give me insight into the fixes they have applied?

If the cars were cheating to defeat IM tests, wouldn't making them not cheat make them fail (or nearly fail) IM tests? Are these cars likely to fail the tests as they age?

Did VW actually fix the IM problem instead of using the software to defeat the tests? If so, it seems like the fix wasn't all that hard and it might have been easier to fix them than to cheat in the first place.

3 comments

There's a tradeoff in these (many? most? all?) diesel engines between better emissions performance and better mileage. The cheat was that the software would tune the engine for mileage normally, except when it detected that it was being tested it would tune the engine for lower emissions. The fix is to lock them into the low-emissions mode.

My rough understanding from reading the discussions at the time is that they can pull the engine into a performance range that passes the emissions test, but that range is 1) less horsepower, fewer lb-ft of torque and 2) worse fuel economy. Diesel as a technology suffers from more NOx production than gasoline because the increased compression forces it to run lean rather than at stoichiometric ratios. So, basically they tell the injection software to run in emissions test mode all the time and it's "fixed" but you're not going to get any of the other claimed numbers.

There's an episode on this on Dirty Money (Netflix), which might answer your question. IIRC, "fixing" it would impact performance/fuel economy.