# I2C Bus Number Changed Unexpectedly on Jetson Orin Nano **URL:** \ **Category:** Jetson Orin Nano\ **Tags:** hw, i2c\ **Created:** [March 6, 2025, 1:00pm UTC](https://forums.developer.nvidia.com/t/i2c-bus-number-changed-unexpectedly-on-jetson-orin-nano/326222 "2025-03-06T13:00:49Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![sweet1674](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@sweet1674](https://forums.developer.nvidia.com/u/sweet1674)\ **Post date:** [March 6, 2025, 1:00pm UTC](https://forums.developer.nvidia.com/t/i2c-bus-number-changed-unexpectedly-on-jetson-orin-nano/326222/1 "2025-03-06T13:00:49Z")
Hello, I’m using a Jetson Orin Nano Developer Kit with JetPack 6.2 (L4T 36.4.3) and have encountered an unexpected issue with the I²C bus numbering. 🛠️ Issue Description According to ' **Jetson Orin Nano Developer Kit Carrier Board Specification’** , pins 3 and 5 (I2C1\_SDA & I2C1\_SCL) on the 40pins expansion header should be assigned to `/dev/i2c-1` while pin 27 and 28 should be assigned to i2c-0. However, after a fresh JetPack installation, these pins are now assigned to `/dev/i2c-7` instead of `/dev/i2c-1` while pin 27 and 28 is assigned to i2c-1. I have confirmed this by running `ls /dev/i2c-*` and `i2cdetect -y 7`, which detects my connected device correctly. 🧪 Steps Taken to Troubleshoot 1. Flashed JetPack 6.2 using SDK Manager (Clean installation) 2. Checked device tree mappings (`/proc/device-tree/aliases/i2c*`) → `/dev/i2c-7` is mapped to `c250000.i2c`, while `/dev/i2c-1` is mapped to `c240000.i2c`. 3. Verified I²C pinmux settings (`/sys/kernel/debug/pinctrl/.../pinmux-pins | grep -i i2c`) → No issues detected. 4. Performed “Reset Settings in NVIDIA Configuration” in UEFI\*\* → No change in behavior. ❓ Questions 1. Has NVIDIA **officially changed the I²C bus numbering in JetPack 6.2**? 2. If not, what could be causing this remapping? 3. Is there a way to restore the default I²C bus mapping (`/dev/i2c-1` for pins 3,5) without manually altering the device tree? This behavior is unexpected, and I haven’t found any relevant discussions regarding this issue. If this is an intentional change in JetPack 6.2, I would appreciate any official confirmation or documentation regarding this update. Thanks in advance for your help! ---
**Author:** ![ShaneCCC](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/shaneccc/32/14043_2.png) [@ShaneCCC](https://forums.developer.nvidia.com/u/ShaneCCC)\ **Post date:** [March 7, 2025, 2:12am UTC](https://forums.developer.nvidia.com/t/i2c-bus-number-changed-unexpectedly-on-jetson-orin-nano/326222/3 "2025-03-07T02:12:13Z")
Which release do you compare to? Maybe you compare to Nano. > **[NVIDIA Jetson Orin Nano GPIO Header Pinout - JetsonHacks](https://jetsonhacks.com/nvidia-jetson-orin-nano-gpio-header-pinout/)** > > JetsonHacks is a site devoted to developing on the NVIDIA Jetson Development Kits. > **[NVIDIA Jetson Nano J41 Header Pinout - JetsonHacks](https://jetsonhacks.com/nvidia-jetson-nano-j41-header-pinout/)** > > JetsonHacks is a site devoted to developing on the NVIDIA Jetson Development Kits. ---
**Author:** ![sweet1674](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@sweet1674](https://forums.developer.nvidia.com/u/sweet1674)\ **Post date:** [March 7, 2025, 6:58am UTC](https://forums.developer.nvidia.com/t/i2c-bus-number-changed-unexpectedly-on-jetson-orin-nano/326222/4 "2025-03-07T06:58:00Z")
I’m testing I2C on the expansion header on Jetson Orin Nano. Until a few days ago, I2C pins 3 and 5 responded on bus number 1. Then suddenly, a few days ago, there was no response on bus 1. In confusion, I looked into it and found that the bus number of pins 3 and 5 had changed to 7, and the bus number of I2C pins 27 and 28 had changed from 0 to 1. So what I’m wondering is: - Why did the I2C bus number for those pins suddenly change? - And is it possible that the I2C bus number for those pins will change again? ---
**Author:** ![ShaneCCC](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/shaneccc/32/14043_2.png) [@ShaneCCC](https://forums.developer.nvidia.com/u/ShaneCCC)\ **Post date:** [March 10, 2025, 6:40am UTC](https://forums.developer.nvidia.com/t/i2c-bus-number-changed-unexpectedly-on-jetson-orin-nano/326222/5 "2025-03-10T06:40:43Z")
Suppose the bus number is 7 from the begging. ---
**Author:** ![system](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/system/32/68080_2.png) [@system](https://forums.developer.nvidia.com/u/system)\ **Post date:** [March 24, 2025, 6:41am UTC](https://forums.developer.nvidia.com/t/i2c-bus-number-changed-unexpectedly-on-jetson-orin-nano/326222/6 "2025-03-24T06:41:33Z")
Closed on March 24, 2025, 6:41am UTC This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.