The Raspberry Pi is a low cost, credit card sized computer that has exploded in popularity among DIY enthusiasts, students, and hobbyists. With over 30 million devices sold, the Pi offers an affordable and accessible way for people to learn programming and build their own projects.
However, like any computer, the Raspberry Pi can sometimes encounter errors during setup, configuration, or general use. These errors can frustrate users, especially beginners who are just getting started with the platform.
One common error on the Raspberry Pi is the somewhat vague “Error 121.” This error can pop up during the initial setup of the Pi, when installing an operating system, or even when trying to boot the Pi after it had been working normally.
What is Error 121?
Error 121 on the Raspberry Pi is an IOError that indicates a remote I/O error occurred during I2C communication between the Raspberry Pi and a connected I2C device like a sensor or display. The full error that typically appears is “IOError: [Errno 121] Remote I/O error”.
This error usually occurs when there is an issue with the I2C wiring connections between the Raspberry Pi and the I2C device. Some common causes are loose connections, wires connected to the wrong pins, improper pull-up resistor values, or excessively long wires. It can also occur due to software issues like an incorrect device address or bus number.
Overall, error 121 signifies a communication problem over the I2C bus, almost always stemming from improper physical connections or configuration. It appears during I2C operations like scanning the bus or reading/writing data. The Raspberry Pi is unable to complete the I2C transaction due to not getting a proper response from the connected device.
Causes of Error 121
There are several potential causes of the error 121 on Raspberry Pi devices:
Outdated or incompatible firmware on the Raspberry Pi can lead to error 121 when trying to communicate over the I2C bus. Keeping the firmware up-to-date through sudo apt-get update and sudo apt-get upgrade can help resolve firmware-related issues.
SD card problems like corruption or inadequate read/write speeds could also trigger error 121. Replacing the SD card with a high-quality, recommended model may fix intermittent I2C issues.
An inadequate power supply that can’t provide enough stable power to the Raspberry Pi is another cause. Using an official Raspberry Pi power supply or a high-quality third party adapter that provides at least 2.5A via the USB-C port is recommended.
Proper wiring and connections to I2C devices is also crucial – faulty or loose wires can intermittently cause error 121 during I2C communication. Checking wiring against pinouts and re-seating connections may help.
Fixes and Solutions
There are several potential fixes and solutions for Error 121 on Raspberry Pi:
One option is to update the firmware on the Raspberry Pi. This can sometimes resolve bugs or issues that are causing Error 121. Updating to the latest firmware ensures compatibility with peripherals and accessories.
Another potential fix is to reformat the SD card being used with the Raspberry Pi. Reformatting will wipe the card clean and allow for a fresh OS install, which can eliminate software issues contributing to Error 121.
If reformatting the SD card does not work, the next step would be to replace the SD card altogether. SD cards can become corrupted or damaged over time, leading to errors. Replacing the card with a new, high-quality SD card may resolve Error 121.
Finally, checking or replacing the power supply for the Raspberry Pi is recommended. An inadequate power supply can cause a range of errors and problems. Swapping in a new official Raspberry Pi power supply can provide stable, sufficient power to prevent Error 121.
Preventing Future Error 121 Issues
Error 121 can often be prevented in the future by taking some basic precautions:
Keep the Raspberry Pi firmware up-to-date. Run sudo apt update and sudo apt full-upgrade regularly to install the latest firmware, which may fix bugs that could cause Error 121.
Use a good quality SD card from a reputable brand. Lower quality or counterfeit SD cards are more prone to corruption that could lead to I/O issues like Error 121.
Use an appropriate power supply that provides stable, clean power to the Pi. An underpowered supply can cause power fluctuations that disrupt I2C communications.
Additionally, reflashing the SD card with a fresh OS install can clear any underlying OS corruption that may be contributing to Error 121.
Diagnosing the Exact Cause
Debugging error 121 requires testing different components to isolate the root cause. Logs and debug information can provide clues, but hands-on troubleshooting is often necessary.
First, check any available logs such as /var/log/syslog or dmesg output for relevant error messages. These may point to issues with specific hardware components or drivers 1. Try adding additional debug output or logging to your software as well.
Next, test key hardware components individually. For example, try reseating the SD card or using a different card to rule out corruption 2. Swap out cables, boards, or modules if possible to isolate the problem.
For I2C related issues, verify connections and use a logic analyzer or I2C scanning tools like i2cdetect to check communication 3. This can identify bus errors and non-responding devices.
By methodically testing and substituting components, you can determine the exact hardware or software issue leading to error 121.
Error 121 on Initial Setup
One of the most common times Error 121 occurs is during the initial setup and boot of a new Raspberry Pi. There are two main causes of Error 121 in this scenario:
Bad image file – This error can occur if the Raspberry Pi OS image loaded on the microSD card is corrupted or damaged. Writing a bad image to the card can result in Error 121 on first boot. The fix is to re-download the image and write it to the card again.
Incompatible hardware – Trying to boot the Pi with incompatible hardware like certain wireless adapters can trigger Error 121. The solution is to remove the incompatible hardware and reboot.
Other Common Raspberry Pi Errors
In addition to Error 121, there are some other errors that commonly occur with Raspberry Pi devices and setups:
One source notes a few other common errors like Error 113 and Error 7. Error 113 relates to issues with reading or writing files to the SD card, often indicating a corrupted SD card that needs reformatting. Error 7 comes up when the kernel is unable to boot and initialize the system, potentially due to an incompatible operating system image.
Another useful source on Raspberry Pi errors goes over problems like the rainbow screen on boot which can mean issues with the GPU or display drivers. It also covers the lightning bolt symbol that indicates undervoltage issues. These other common errors are good to be aware of when troubleshooting Raspberry Pi projects.
When to Seek Additional Help
If basic troubleshooting like checking connections and wiring does not resolve the Error 121, it’s time to seek additional help. Intermittent or recurring Error 121 issues after trying fixes likely indicate an underlying problem that requires advanced technical skills to properly diagnose and repair.
Seeking help on Raspberry Pi forums or Stack Overflow can provide useful tips, but won’t guarantee a solution. For persistent Error 121 problems, especially on an important project, it may be best to consult a professional technician or engineer with Raspberry Pi and Linux experience.
A technician can perform in-depth debugging and hardware testing beyond basic checks. They may identify obscure software issues, power problems, faulty components, or other root causes an amateur would likely miss. Their expertise allows properly diagnosing and permanently fixing the issue, rather than just temporarily alleviating symptoms.
While hiring a professional costs money, it can save time and frustration compared to endless trial-and-error troubleshooting. For business, scientific, or mission-critical Raspberry Pi projects, bringing in outside expertise makes sense to debug elusive issues like recurring Error 121.
Conclusion
In summary, Error 121 on the Raspberry Pi is a general error that indicates the system is unable to read or write to the SD card. This is often caused by a corrupted SD card, improper shutdowns, faulty card readers/writers, or incompatible SD cards. While frustrating, Error 121 can often be resolved by reimaging the SD card, checking connections, trying a different SD card, or tweaking config settings.
To avoid Error 121 in the future, make sure to properly eject the SD card before removing it, use reputable branded SD cards, update the Pi and OS regularly, and avoid forceful shutdowns. If the error persists, reinstalling the OS or SD card formatter tools may be necessary. While Error 121 typically indicates an SD card issue, other possibilities like faulty hardware could be the culprit.
With some targeted troubleshooting and care when handling the SD card, Error 121 can usually be fixed allowing you to get back to your Raspberry Pi projects. Just remember to keep multiple backups of your SD card images to simplify recovery when needed.