O2 downstream sensor

TANIK

MEMBER
2018 HYUNDAI TUCSON
0.5L
4 CYL
2WD
MANUAL
30,000 MILES

My car has judder on cold start when you pull away from first gear. This happen only when the weather is cold or wet. There is no light on dash, no error code. I have obd2 scan tool and I have notice that on cold start my o2 sensor 2 (downstream) is not responding in first 15 minutes while the upstream start to measure in 1m. After downstream will start showing voltage the issue is gone and car runs smoothly. My question is, should downstream sensor start working sooner and can be that cause of my judder when the car is start from cold?

4 Replies

TANIK

MEMBER
3 POSTS

Screenshots from scan tool:

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Saturday, December 28th, 2019 AT 11:22 AM

KASEKENNY

MECHANIC
18,907 POSTS

Excellent job with the graphs and noticing this information. However, the downstream sensor is not used until the vehicle goes into closed loop so I would not expect to see it reading in the PCM until this is needed. The thing you monitor is the loop status in the scan tool and when this stops doing it. If when it goes to closed loop it stops then we need to start looking at sensor data that is used during open loop.

However, if you can duplicate this, you need to take it to a dealer because based on time and mileage it is still under warranty. I would take it to them and make sure they get it corrected.

As for it not happening when the downstream comes on, that tells me that the PCM controlled programming is either flawed or is getting bad info from an input sensor. It looks at MAP data, ECT, BARO, and ICT. If one of these is inaccurate then it will cause issues until the PCM starts looking at o2 data. Let me know what this info says on the scan tool and we can go from there.

Or if you take it to a dealer, let me know what they say. Thanks

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Saturday, December 28th, 2019 AT 5:54 PM

TANIK

MEMBER
3 POSTS

Hi Kasekenny1.

Thanks for your replay. I just recorded a video from cold start (2°C outdoor temperature ) with torque pro android app. Looks like there is no data for open/closed loop, but you can see all other sensors data that the app is able to recognize. Yes my car is under warranty but the dealer 'can't' reproduce the issue and is not interested to fix it because there is no any DTC code. Please tell me if you can notice any strange behavior from data presented in the video attached. Thanks

Edit: if you have problem with attached video, you can find it on youtube https://youtu.be/p1qiAp_MESk

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Wednesday, January 1st, 2020 AT 2:38 PM

KASEKENNY

MECHANIC
18,907 POSTS

I circled a data point. It looks like a temp sensor but it says -39.5 C. If the temp is 2 C then this would be an issue we need to investigate.

It is normal for dealers to not want to make a repair if they can't duplicate a concern but if you can get this to happen then I would call the service manager and have him and the technician go for a ride with you so you can show them what it is doing. Then show them this sensor if that is in fact a temp sensor.

It is typical for a temp sensor to should -40 when it is a sensor issue. This typically means the sensor is an open circuit but is giving a reading so it won't set a code. If the sensor is reporting this temp to the ECM then it can cause shifting issues or other performance issues.

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