Hyundai Elantra Fuel System Diagnostics

Hyundai Elantra Fuel System Diagnostics

We recently had a 2011 Elantra in for a check engine light complaint motivated by the fact that it was due for a New York state inspection. This high-mileage car was owned by one of our good customers. It has served him well with no driveability complaints and, with only 175,000 miles on the odometer, he was hoping it would not be an expensive repair.

We recently had a 2011 Elantra in for a check engine light complaint motivated by the fact that it was due for a New York state inspection. This high-mileage car was owned by one of our good customers. It has served him well with no driveability complaints and, with only 175,000 miles on the odometer, he was hoping it would not be an expensive repair. The job was assigned to one of the young techs who found a P2096 code (post cat fuel trim lean).

Our usual procedure is to look at the freeze-frame data, clear the code and perform the drive cycle to see if the code returns. Hyundais are sensitive to downstream exhaust leaks that will have us getting some post cat trim codes. Our tech checked for exhaust leaks, but found the system to be leak free. At this point, the car was taken for the first drive cycle, and after the first drive there were three monitors that did not set. After a cool-down period, the car was driven again with P2096 returning within three miles.

At this point, I asked to see the freeze-frame data only to be told that it was never printed out or reviewed. As you might expect, I was not happy about that and was even more disappointed that the current code had already been cleared without accessing the information. I could have handled this situation in a couple of ways, but chose to use it as a teaching opportunity. A recent graduate from a tech school, the tech did not seem to understand why this information was so important. My frustration increased when I asked what he had for fuel trims and O2 outputs, and found out he didn’t look at them either, only the monitors.

hyundai sonata fuel trim
Live data image: Choose the parameters you want to look at to get a faster refresh rate. I like to move the ones I’m most interested in to the top of the screen.

Back in the Elantra with me driving and the young tech looking at the scanner, we reviewed how to bring up the parameters and how and why we chose only the parameters we were interested in. He seemed to understand that the reason for only looking at the parameters we were interested in is because it gives us a faster refresh rate, as well as makes it easier to look at the data on one screen. At the same time, I showed him the “to the top” button that will put the parameters in a list — the way you want them. It has been 46 years since I graduated from trade school and I often find myself saying I wish I paid better attention. I guess some things never change from one generation to the next.


Next, we discussed what parameters we should be looking at. He knew the code was related to the rear O2 fuel trim but he had not taken advantage of the repair information the shop has available. This was only getting worse for the kid. We decided we would look at AFR and rear O2 output, as well as front and rear fuel trims. With the vehicle warmed up, we looked at our parameters in display (PIDs).

The front AFR was showing negative 1-2 mA slightly rich. It would respond to hard acceleration and coast down so the sensor was working, while the rear O2 was showing a steady 0.76 volts and also responding as expected. With both sensors working as anticipated, we had a slightly negative biased front trim almost near zero, but we were surprised to see a big positive 30% trim on the rear sensor.

Back at the shop, I sent him to the computer to see what information was available. We have a good selection of online service information, and it should be the first place to start once you identify the code. We don’t use these services as a silver bullet, rather, it is more like taking advantage of someone else’s experience to help confirm what the car needs. I am pleased to say that at least when the tech looked at our service information, he was able to identify that most folks facing the same issue took care of this code with a software update. However, what he did not do was look up the TSB that contained the details.

So, we looked at the bulletin together — it included the list of the current calibration numbers that should be updated. From there, we went back to the car to get the current calibration. As we looked at the menu, I suggested he choose the ECU information area where he found the calibration, and it did not take long to see that the ECU needed an update. We did not start flashing right away, since we really did not have a lot of call for it at this point, but it is something we should have probably started to think about.

Checking with the local dealer, the customer would have to pay for the flashing service and, with so many miles on the vehicle, any warranty was well expired. But, the dealer did mention the vehicle had an open recall and suggested that it be brought in. The customer was reluctant to take his car to the dealer; he didn’t have the best experience in the past and was concerned about what he considered a high-pressure upsell. We did convince him that it had to be done to pass the state inspection and all he had to do was say “no” to any upsell attempts. I am pleased to say that with the update completed, the Elantra was ready for inspection; unfortunately, our customer did have to decline a suggestion that the O2 sensors be replaced based on age and mileage (I’m assuming).

hyundai elantra fuel trim

When it was all said and done, the customer was pleased, our newest tech learned something and I even learned that our new tech could use some more training time. Undoubtedly, this business requires our willingness to never stop learning and to take advantage of our best resources.

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