The major difference between LSU 4.9 and 4.2 is that LSU 4.9 uses the reference pumping-current, while LSU 4.2 uses the reference air. What does this mean? Let’s read this true story from the auto industries: when Bosch first designed a wideband oxygen sensor, a reference air cell was used to provide a reference of stoic AFR. The technology was to keep the pumping cell balanced with the reference air cell, by pumping the oxygen out of the pumping cell. The pumping current was the indication of the actual AFR in the exhaust gas. The bigger the pumping current, the more the oxygen in the exhaust, and vice versa. Therefore the reference air was vital to the accuracy of the sensor, because it was THE reference. It worked well in the lab, but not so good in the real life, because the environment around the sensor on a car was much worse. The reference air cell was susceptible to be contaminated by the surrounding pollution. Once the reference air was contaminated, the whole characteristic s of the sensor were shifted to the lower side. It was called “Characteristic Shifted Down”, or CSD, in the industries. This was the biggest problem of LSU 4.2 that was used in some early OEM applications. And it caused the big quality issue to Bosch. To fix this problem, Bosch redesigned the LSU sensor, and came up with LSU 4.9 version. LSU 4.9 sensor completely got rid of the reference air. Instead, it used a reference pumping current which was equivalent to the stoic reference air, but without having any physical air in the cell. So the technology became: the actual pumping current was compared to the reference pumping current to maintain the balance. The actual pumping current was still the indication of the actual AFR, but the reference was a calibrated electrical signal, and stayed same all the time, all the situations.
LSU 4.9 gets rid of the reference air, and therefore gets rid of the biggest failure mode. As a result, LSU 4.9 has a long life and can maintain the accuracy throughout the life. Only since then, Bosch LSU sensors have been used widely in the auto industries.
Nowadays, all OEMs who use Bosch O2 sensors are using LSU 4.9. GM, Ford, and Chrysler all use LSU 4.9 now. If you check out the O2 sensors on your recently bought vehicles, cars/SUVs/Pickups, (since 2007 or later), on the exhaust manifolds, you will find out that they are all exclusively LSU 4.9. No more 4.2 sensors can you find on OEM vehicles.
Most aftermarket wideband controllers are still using LSU 4.2, mainly for low cost reasons. Bosch sells the LSU 4.2 to the aftermarket at a much lower price than LSU 4.9. Plus, many of those companies do not want to or are not able to adapt the new LSU 4.9 sensors. There is a big mis-understanding that LSU 4.9 is only for diesel engines, because it can measure very lean AFRs. That’s not true. There is a diesel version of LSU 4.9, called LSU4.9D, mainly because of fuel and temperature difference. LSU 4.9 has been widely used with the gasoline engines. In fact, it is the most popular gasoline engine O2 sensor now, not only because it measures wide range of AFR, but also because it has the very good reliability, and high accuracy.
There are a few wideband controller companies in the aftermarket using LSU 4.9. But that does not mean all controllers using LSU 4.9 are equal. Even with the same LSU 4.9 sensor, the controller can make a big difference. Some wideband controllers are designed for AFR display only, and they are named as “wideband AFR gauges” instead of controllers. You can imagine that those wideband gauges do not have good accuracy and fast response rate because they are not designed for those purposes. Those gauges are more for good looking than for engine tuning purposes. For engine controls, the accuracy and response rate are the most critical characteristic s of a wideband controller. One way to tell whether a wideband controller is good or not, is to see whether it can be used as a feedback device for the ECU. A feedback device must provide a real-time signal in the fast rate and high accuracy, even under dynamic situations. The requirements for a feedback device are much, much more than those for a gauge.
Even with a LSU 4.2, the controller makes a big difference. Bosch sensors are not easy to fail even with a LSU 4.2, if controlled appropriately. Especially, LSU 4.9 is designed for more than 10 year life because it has to, for the vehicle life. It should not fail in short time, like a couple of years. Many OEM cars have been running with LSU 4.9 for years and we have not heard any recalls because of LSU4.9 sensors. Why do so many aftermarket wideband systems have failed LSU sensors? Because many of them don’t have a good heating control strategy.
The number 1 failure mode of a LSU sensor is being heated up too fast or too earlier. O2 sensors are made of ceramic materials, which can be damaged by severe thermal shocks, like condensations, liquid residuals, or just high heating power when it’s still cold. A very carefully designed heating strategy to detect the dew point and a close-loop sensor temperature control are vital for the life of the sensors. That’s why the LSU sensor must be controlled in the context of engine controls. You may say, only those who know engine controls can design a good wideband controller.
Furthermore, the accuracy of LSU sensors is highly dependent on the operating temperature of the sensing element. The sensor reading can be very different if the temperature of the sensing element is different. LSU sensors must work at the vicinity of certain temperatures for the good accuracy. LSU4.9 sensor must be maintained at 780 degrees Celsius precisely.
Bosch CJ125 chip is designed for this task. The heating strategy is a close loop control based on the measured sensor temperature. PLus, LSU 4.9 has a much higher sensor temperature resolution because of the resistance characteristic s, so the heater controls are much better than LSU 4.2. As a result, 4.9 has a longer life and better accuracy.
In every Bosch LSU sensor data sheet (4.2, 4.9 or ADV), it is clearly stated:”The wide band sensor LSU operates only in combination with a special LSU control unit (CJ125 ASIC). The functional characteristic s given in this document are only valid for operation with the CJ125 according to module specification and with recommended operational parameters.” Bosch means it. Anybody who tried to design a cheaper circuit and claimed it better ended up with a less quality one! Because Bosch simply had done that to the extreme. The cost in auto industry is everything. If there would have been a way to save another penny in the sensor control circuit, Bosch would have done it with the CJ125 chip. If some after-market vendors could design a better control circuit to control the LSU sensor and it would be cheaper, they could sell that “invention” to Bosch.
If you are still not sure, you can use an oscilloscope to actually measure the analog outputs of different wideband controllers if you really want to see the difference. Data do not lie.
Don’t forget, when you use a scope, you better set the time scale in 10ms or smaller. If you have a time scale of 100ms or more, then there could be no difference for any controllers.
