# I2c is not detectable on Rpi 400 or Rpi 4 but is with Rpi 3s

**URL:** <https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651>\
**Category:** Hardware\
**Created:** [3 December 2021 01:03 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651 "2021-12-03T01:03:02Z")\
**Posts on this page:** 11\
**Page:** 1

<div class="post-metadata">

**Author:** ![Loonhaunt](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/loonhaunt/32/34517_2.png) [@Loonhaunt](https://discourse.nodered.org/u/Loonhaunt)\
**Post date:** [3 December 2021 01:03 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/1 "2021-12-03T01:03:02Z")

</div>

I is there some thing that I am missing? I am having a bugger of a time getting i2cdetect -y 1 to find anything on raspberry pi 4s or 400s

Dave

---

<div class="post-metadata">

**Author:** ![Trying\_to\_learn](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/trying_to_learn/32/28400_2.png) [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)\
**Post date:** [3 December 2021 08:06 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/2 "2021-12-03T08:06:57Z")

</div>

Hi.

Make sure you have enabled the I2C option in the `raspi-config` menu.

It it isn't enabled there, you are not going to get anywhere I feel.

Sorry if you have done it, but it is better to _state the bleeding obvious_ than not. 😉

---

<div class="post-metadata">

**Author:** ![Loonhaunt](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/loonhaunt/32/34517_2.png) [@Loonhaunt](https://discourse.nodered.org/u/Loonhaunt)\
**Post date:** [3 December 2021 12:44 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/3 "2021-12-03T12:44:56Z")

</div>

I did do that several times. You are correct to master the obvious first. The pi 400 magically started up last night (i2c) I It took several reboots.

Dave

---

<div class="post-metadata">

**Author:** ![cymplecy](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/cymplecy/32/2773_2.png) [@cymplecy](https://discourse.nodered.org/u/cymplecy)\
**Post date:** [3 December 2021 14:07 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/4 "2021-12-03T14:07:47Z")

</div>

I'd suspect a loose connection somewhere could be causing your issue

---

<div class="post-metadata">

**Author:** ![ghayne](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/ghayne/32/39_2.png) [@ghayne](https://discourse.nodered.org/u/ghayne)\
**Post date:** [3 December 2021 14:32 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/5 "2021-12-03T14:32:24Z")

</div>

Like @cymplecy said or have you forgotten the pull - up resistor?

---

<div class="post-metadata">

**Author:** ![cymplecy](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/cymplecy/32/2773_2.png) [@cymplecy](https://discourse.nodered.org/u/cymplecy)\
**Post date:** [3 December 2021 17:54 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/6 "2021-12-03T17:54:37Z")

</div>

The Pi has built in pull-ups on the i2c pins

---

<div class="post-metadata">

**Author:** ![ghayne](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/ghayne/32/39_2.png) [@ghayne](https://discourse.nodered.org/u/ghayne)\
**Post date:** [3 December 2021 17:56 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/7 "2021-12-03T17:56:47Z")

</div>

Yep, should have remembered that!

---

<div class="post-metadata">

**Author:** ![Loonhaunt](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/loonhaunt/32/34517_2.png) [@Loonhaunt](https://discourse.nodered.org/u/Loonhaunt)\
**Post date:** [3 December 2021 20:21 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/8 "2021-12-03T20:21:56Z")

</div>

The Rpi 400 detected the i2c BUS as soon as I did full upgrade and then upgraded to --node16 Node-RED. Don't ask me why. I am just happy to be back online. I am going to hold off on Bullseye and "OS Legacy" as long as my current Buster revs are doing what I need on my hardware. Too many fish to fry at the moment.

Dave

---

<div class="post-metadata">

**Author:** ![Trying\_to\_learn](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/trying_to_learn/32/28400_2.png) [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)\
**Post date:** [3 December 2021 21:21 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/9 "2021-12-03T21:21:37Z")

</div>

Good to hear all is now good. 🙂

---

<div class="post-metadata">

**Author:** ![cymplecy](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/cymplecy/32/2773_2.png) [@cymplecy](https://discourse.nodered.org/u/cymplecy)\
**Post date:** [4 December 2021 06:46 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/10 "2021-12-04T06:46:29Z")

</div>

I have several PiZero running Jessie and very old NR versions 🙂  
They do the job I need them to and I leave them alone 🙂

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [18 December 2021 06:46 UTC](https://discourse.nodered.org/t/i2c-is-not-detectable-on-rpi-400-or-rpi-4-but-is-with-rpi-3s/54651/11 "2021-12-18T06:46:49Z")

</div>

This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.