The Nexus 4 Red Light issue is well documented by searching Google, but there is A LOT of misinformation out there. This is an attempt to show how I solved the Nexus 4 Red Light issue, and to explain in detail the Nexus key combinations and their functions and timings.
First, the problem. My Nexus 4 was running low on battery, hitting 13%, so I plugged in to a USB port on my Laptop. The phone started charging so it became out of sight, out of mind. About four hours later, I see the phone screen flash a logo stating that the phone is now in Download Mode and not to disconnected it from the computer. The phone was also unresponsive at this point, had the red light showing, and not recognized by the computer at all, even through adb. To be fair, I have been having power and connectivity issues with the Nexus 4 lately where the phone wouldn't charge when connected to the laptop and would not be recognized. This is an issue with the phone, not the computer as I have tried to connect the phone to more than 5 different PCs and nothing (Windows, Linux, or Mac) will recognize anything even being plugged in. Another issue for another day.
Since the phone was not responsive, I pulled the plug. Download Mode continued to show on the screen, red light continued to glow, so I figured I should do a simulated battery pull key combination.
Key combinations for the Nexus 4:
Battery Pull - Battery pull is simulated by holding the Power key for 10, 15, or 60 seconds. The timing depends on the state that the phone is in. If the phone is booted normally and an app or process hangs the phone, press and hold the power button for 10 seconds, the phone will restart. If the phone is stuck in a bootloop or in Recovery Mode, then long press for 15 seconds will shut the phone off. If the phone is soft-bricked, has the red light showing, or is in Download Mode, then long press for 60+ seconds will simulate a battery pull.
Recovery Mode - With the phone off, press Power + Volume Down to boot into Recovery Mode.
Download Mode - You can't actually boot into this unless your phone is in a very specific state. Long press Power + Volume Up WITH a USB cable connected. To get to this state, the battery has to be removed or has to be beyond dead. There is no utility I could find similar to Odin/Heimdall to use this, so largely irrelevant, but possible.
Some detail about the red light on the Nexus 4.
Flashing red light - Battery is completely drained, not enough power to start the phone of fastboot. When connected to a charger, battery will charge, but it will only trickle-charge. Blinking also means that the battery voltage is not too low for the battery to charge. Blinking red light can happen when he USB cable is both plugged an unplugged and indicates that the battery voltage is too low to attempt to start and needs plugged in. Booting into recovery is possible, but not recommended as the screen + system will use more power than the charger can supply.
Solid red light - When plugged in, this means that the battery is trickle charging. Be careful with this though, if you are using an aftermarket charger, the battery may not be charging because the voltage is too low. I measured three different aftermarket chargers to only be between 3.8V and 4.4V. The Nexus 4 charger outputs 5.1V, and this was a noticeable difference. A solid red light also indicates that the battery voltage is too low to attempt a start, even with fastboot, and booting to recovery is not going to happen.
How to tell just how dead your battery is. If the red light goes out when pushing Power + Volume Down without the USB cable plugged in, then the battery is most likely less than 0%.
The Fix:
It is critical to know what state the battery is in before starting the fix.
Use of the original Nexus 4 charger is a must! The charger power supply must be 4.8V or above for this to work.
All fix steps require the use of the wall charger! Plugging the phone into the computer can't provide the current required to initially charge the battery.
If the battery is less than 0%, then a battery pull is required to "reset" the phone. Battery pull can be simulated or physical.
For a simulated battery pull, just hold the power button down for 60+ seconds with the USB cable plugged in to the charger. After 60+ seconds, let go of the power button then unplug and replug the USB cable. The red light should come on and be solid.
A physical battery pull can be used as well. The two screws at the bottom of the Nexus 4 need to be removed, followed by the back casing. Inside the phone, remove the two screws holding the battery flex cable into the phone, and pop the connector off. Then reconnect the flex cable and insert the USB cable. The red light should come on and be solid.
This video shows the process, start at the 2:40 mark.
https://www.youtube.com/watch?v=IWABgDHvfx0
The red light has to be on for the battery to be charging. In my experience, the red light would go off after about ten minutes, just unplug the USB cable and replug it withing 5 seconds.
After about an hour the screen will flash, the white battery icon will show shortly, then the screen will go off and the solid red light will be on. This just indicates that the system recognizes the battery is at 0% and trickle charging will continue until the battery is around 15%. At this point, it would be safe to boot the system. Booting into Recovery Mode is not required at this point, but letting it charge further is recommended.
At any time during charging, with the phone off, if the charge indicator LED is not illuminated, unplug and replug the USB cable.
I let my phone charge overnight, my progress went as follows:
Flashing red light - Partial boot to logo then power off. Did a simulated battery pull, unplug then replug USB cable to get the solid red light.
Solid red light - Phone charged for about 10 minutes, then the light went out. Unplug and plug USB cable and red light came back on for about 20 minutes. Screen then turned on with white battery icon for 15 seconds, then turned off and solid red light came back one. Phone continued charging for another hour and a half. I did not short-press the power button to get the battery status as I did not want to mess anything up.
Yellow/Orange light - Phone switched from solid red light to solid yellow/orange and charging continued. Total time spent with yellow/orange was about 3 hours. I did not short-press the power button to get the battery status as I did not want to mess anything up.
Green - Phone then switched to green and charging topped off the battery. When the phone switched to green, I short-pressed the power button and saw the battery was at 90%. After 30 minutes, the battery was at 100%.
I turned on the phone and everything seemed to be normal until the final loading of the OS. All of the applications had to load, then the phone started up normally and everything was in the right place.
First, the problem. My Nexus 4 was running low on battery, hitting 13%, so I plugged in to a USB port on my Laptop. The phone started charging so it became out of sight, out of mind. About four hours later, I see the phone screen flash a logo stating that the phone is now in Download Mode and not to disconnected it from the computer. The phone was also unresponsive at this point, had the red light showing, and not recognized by the computer at all, even through adb. To be fair, I have been having power and connectivity issues with the Nexus 4 lately where the phone wouldn't charge when connected to the laptop and would not be recognized. This is an issue with the phone, not the computer as I have tried to connect the phone to more than 5 different PCs and nothing (Windows, Linux, or Mac) will recognize anything even being plugged in. Another issue for another day.
Since the phone was not responsive, I pulled the plug. Download Mode continued to show on the screen, red light continued to glow, so I figured I should do a simulated battery pull key combination.
Key combinations for the Nexus 4:
Battery Pull - Battery pull is simulated by holding the Power key for 10, 15, or 60 seconds. The timing depends on the state that the phone is in. If the phone is booted normally and an app or process hangs the phone, press and hold the power button for 10 seconds, the phone will restart. If the phone is stuck in a bootloop or in Recovery Mode, then long press for 15 seconds will shut the phone off. If the phone is soft-bricked, has the red light showing, or is in Download Mode, then long press for 60+ seconds will simulate a battery pull.
Recovery Mode - With the phone off, press Power + Volume Down to boot into Recovery Mode.
Download Mode - You can't actually boot into this unless your phone is in a very specific state. Long press Power + Volume Up WITH a USB cable connected. To get to this state, the battery has to be removed or has to be beyond dead. There is no utility I could find similar to Odin/Heimdall to use this, so largely irrelevant, but possible.
Some detail about the red light on the Nexus 4.
Flashing red light - Battery is completely drained, not enough power to start the phone of fastboot. When connected to a charger, battery will charge, but it will only trickle-charge. Blinking also means that the battery voltage is not too low for the battery to charge. Blinking red light can happen when he USB cable is both plugged an unplugged and indicates that the battery voltage is too low to attempt to start and needs plugged in. Booting into recovery is possible, but not recommended as the screen + system will use more power than the charger can supply.
Solid red light - When plugged in, this means that the battery is trickle charging. Be careful with this though, if you are using an aftermarket charger, the battery may not be charging because the voltage is too low. I measured three different aftermarket chargers to only be between 3.8V and 4.4V. The Nexus 4 charger outputs 5.1V, and this was a noticeable difference. A solid red light also indicates that the battery voltage is too low to attempt a start, even with fastboot, and booting to recovery is not going to happen.
How to tell just how dead your battery is. If the red light goes out when pushing Power + Volume Down without the USB cable plugged in, then the battery is most likely less than 0%.
The Fix:
It is critical to know what state the battery is in before starting the fix.
Use of the original Nexus 4 charger is a must! The charger power supply must be 4.8V or above for this to work.
All fix steps require the use of the wall charger! Plugging the phone into the computer can't provide the current required to initially charge the battery.
If the battery is less than 0%, then a battery pull is required to "reset" the phone. Battery pull can be simulated or physical.
For a simulated battery pull, just hold the power button down for 60+ seconds with the USB cable plugged in to the charger. After 60+ seconds, let go of the power button then unplug and replug the USB cable. The red light should come on and be solid.
A physical battery pull can be used as well. The two screws at the bottom of the Nexus 4 need to be removed, followed by the back casing. Inside the phone, remove the two screws holding the battery flex cable into the phone, and pop the connector off. Then reconnect the flex cable and insert the USB cable. The red light should come on and be solid.
This video shows the process, start at the 2:40 mark.
https://www.youtube.com/watch?v=IWABgDHvfx0
The red light has to be on for the battery to be charging. In my experience, the red light would go off after about ten minutes, just unplug the USB cable and replug it withing 5 seconds.
After about an hour the screen will flash, the white battery icon will show shortly, then the screen will go off and the solid red light will be on. This just indicates that the system recognizes the battery is at 0% and trickle charging will continue until the battery is around 15%. At this point, it would be safe to boot the system. Booting into Recovery Mode is not required at this point, but letting it charge further is recommended.
At any time during charging, with the phone off, if the charge indicator LED is not illuminated, unplug and replug the USB cable.
I let my phone charge overnight, my progress went as follows:
Flashing red light - Partial boot to logo then power off. Did a simulated battery pull, unplug then replug USB cable to get the solid red light.
Solid red light - Phone charged for about 10 minutes, then the light went out. Unplug and plug USB cable and red light came back on for about 20 minutes. Screen then turned on with white battery icon for 15 seconds, then turned off and solid red light came back one. Phone continued charging for another hour and a half. I did not short-press the power button to get the battery status as I did not want to mess anything up.
Yellow/Orange light - Phone switched from solid red light to solid yellow/orange and charging continued. Total time spent with yellow/orange was about 3 hours. I did not short-press the power button to get the battery status as I did not want to mess anything up.
Green - Phone then switched to green and charging topped off the battery. When the phone switched to green, I short-pressed the power button and saw the battery was at 90%. After 30 minutes, the battery was at 100%.
I turned on the phone and everything seemed to be normal until the final loading of the OS. All of the applications had to load, then the phone started up normally and everything was in the right place.
