2009 Volkswagen Jetta TDI
Before the vehicle can be re-registered, the strict CARB may require the car to be made legal. As of today, we have no inkling of how long that could take.
In suspending its Recommended rating on the diesel Jetta and Passat, Consumer Reports notes:
While it is legal to sell the car, CARB and the California Department of Motor Vehicles may not allow the buyer to register the vehicle, and current owners may not be allowed to renew their registrations, until all the emission recall work has been completed.
Some states that follow California emission standards (so-called Partial Zero Emission states) also have rules in place that require all emissions-related recalls to be completed before periodical emission testing. If the recall is not completed, the vehicle cannot pass the inspection, and the state will decline renewal of the vehicle registration.
(4) What exactly did VW do?
Volkswagen has admitted that it equipped the control software for its 2.0-liter TDI diesel vehicles with a "defeat device" that detected when the car was undergoing emissions testing and significantly changed the operations of its powertrain to reduce emissions during the tests.
That detection was likely based on a combination of sensor data from the car, which might include steering angle (since cars on dynamometer tests don't make turns), front-wheel versus rear-wheel rotation speed, and a variety of other factors.
The emission test cycles that were developed in the early 1970s are far less aggressive than virtually any real-world driving 40 years later.
It appears that a combination of the factors above plus extremely gentle acceleration and braking might alert the car that it wasn't on the road but being tested in a lab.
Diesel engines are known to generate nitrous oxides (NOx), as do gasoline engines, but in greater quantities due to their higher operating temperatures.
Based on discussions with knowledgeable sources, we surmise that once an emissions test was detected, VW got the affected TDI engines to meet the Tier 2, Bin 5 NOx limits by reducing the fuel flow rate.
This would reduce performance, but most likely not to the point where the car couldn't complete the emission cycles.
Lowering fuel flow would also reduce combustion temperatures and/or the duration of high-temperature operation enough to keep NOx emissions barely within EPA limits.
If the car detected that it was no longer in "testing mode" but had returned to "driving mode," it would restore fuel flow to the regular level--which would send NOx emissions soaring.
The odd thing is that this software feature seems to have persisted into the company's newest generation of 2.0-liter TDI diesels, a heavily revised design known as EA288, which was intended to be fitted with urea aftertreatment systems--which allow other makers to meet the NOx limits under all circumstances.
The situation is slightly different with the V-6 diesels. They turned out to contain several undisclosed "auxiliary emission control devices," essentially software routines that temporarily limit the emission controls to preserve the engine under transitory extreme operating conditions.
Those are legal, but must be disclosed to the EPA, which they had not been. One of those routine qualifies under arcane EPA definitions as an illegal 'defeat device."
(5) How was it discovered?
This is one of the more interesting parts of the story: It wasn't discovered by the EPA at all, but by a clean-air group that tested VW diesel models to confirm its hypothesis that the latest diesel cars complied with all emissions standards while remaining much more efficient than comparable gasoline cars.
As recounted by Bloomberg, the International Council on Clean Transportation (ICCT) had studied European diesel cars and discovered that the on-road emissions of some models were notably higher than those measured in lab testing.
So the group decided to replicate its tests in the U.S., which then had much stricter emissions limits (known as Tier 2, Bin 5) than the Euro 5 standards in force in the European Union until this year.
They tested the cars on a dynamometer, or "rolling road," then measured their emissions in real-world use with a variety of speeds, road types, and demands on a road trip from San Diego to Seattle.
“We had no cause for suspicion,” John German, the ICCT's U.S. co-lead, told Bloomberg. “We thought the vehicles would be clean.”
The U.S. models too proved to have on-road emissions far higher than the maximum legal limits, so high that German termed the results "shocking."
On the open road, a Volkswagen Jetta TDI blew through the U.S. nitrogen oxide (NOx) emissions limit by 15 to 35 times. A VW Passat TDI (with urea aftertreatment) was 5 to 20 times the maximum.
A BMW X5 xDrive 35d diesel crossover equipped with urea aftertreatment and tested at the same time, however, met the emission limits under all circumstances.
The U.S. EPA and CARB opened a joint investigation into the cars in May 2014, but it was not publicized.
In December 2014, VW recalled nearly half a million cars for a software patch to fix the problem--but CARB found it didn't enable the cars to meet the regulations. Matters came to a head in July 2015, when CARB informed the EPA and VW of its findings.