Use Dell Diagnostic Lights To Troubleshoot Your PC

dell diagnostic lights

Your PC might have Dell diagnostic lights labeled A B C D on the rear that can help you diagnose problems with your Dell machine. Not all models will have these, but if your computer does, you can reference these and quickly repair a problem that might have taken you days to figure out. If your computer does not have lights, it will probably only issue a beep code, which is fine. However, the lights can confirm things a beep code cannot, such as no power to the system.

Dell diagnostic lights

The image above shows a working Dell with all four lights green. If, however, you have anything different, you can look up your model on the Dell website for further documentation on these error codes. We will list a few of the most common here, but there are certainly more on the Dell website.

Dell Diagnostic Lights

Below are some of the common Dell diagnostic lights and their codes. You should refer to the Dell support site to find your specific model and their codes.

A B C D — No lights indicates the system is getting no power. You can confirm the outlet is working, but if you are still not getting power, you could have a problem with either the power supply, front switch or the motherboard itself.

A — If only the yellow ligth is lit, this means the computer is off and receiving power.

A B C – If A B and C are yellow, this means the BIOS is not running or not finishing (completing its POST).

B — If B is yellow, this means you are having some type of issue with the power supply.

C — If C is yellow, this means you have some type of problem with the motherboard.

A B D Yellow and C Green –This means you could have a problem with your CPU.

A B Yellow and C D Green — This means you have memory installed, but there is a problem with it.

These are the top Dell diagnostic lights and their conditions that can prevent your system from booting. You may have different diagnostic lights and still be able to boot, but a lot of those problems can be quickly fixed once you boot up the computer. One important thing you can try if you are receiving any of these critical conditions is to shut the system down, remove the plug and open the case. Make sure you touch a piece of metal on the case’s chassis to ground yourself, then proceed to making sure all cables and cards are secure. Be careful not to touch any chips on the memory or the motherboard in the process.

27 thoughts on “Use Dell Diagnostic Lights To Troubleshoot Your PC”

  1. I have a b c green d yellow….I have no clue what that means. i did as dell said and checked the wires and connections still no boot up. Anyone with any suggestions please let me know. It is a DELL Dimension 4600. Thank you for any responses

    1. I would unplug any external devices and make sure there are no thumbdrives or disks in any of the drives. Is anything coming on the screen at all? I suggest you join our free forums so we can troubleshoot this more.

  2. That’s not uncommon. I would try a new, different brand disk to burn to. CD-R disks work better than CD-RW if that’s what you were using. But I would consider using a USB external hard drive (unless you specifically need to have then on CDs). Hard drives hold more data and are more reliable to archive data over a long time period. Good luck.

  3. I have a Dell Optiplex 170L CPU which is 8 years old. It had developed booting problem during the last few months. The front switch was required to be pressed several times in order to boot the computer. Now it has stopped booting even after trying several times. When tried to switch on the PC, the front power light turns yellow and the CPU activity lamp turns green. After a few seconds (2-8 seconds) both these lights go off. The diagnostic lights (all four) in the rear panel do not glow even when attempted to boot the computer. Kindly let me know what would be the possible trouble and how to shoot the same. Do you think that the front panel power switch is malfunctioning ?

    1. Not sure. I would visit and lookup the manual for your specific model. I encourage everyone do that if they do not have a service manual for their PC. These manuals are priceless in an emergency.

  4. I’m currently troubleshooting a Dell Dimension 24000, it has a yellow D light and all other lights are green. When I power it on I see the Dell load up screen. Then I get a black screen than onl has “strike F1 to retry boot, F2 for setup utility”. I already checked all the cables inside the machine to make sure they were no loose. I also reset the bios, still no luck. So any adivce would be greatly appreciated.

  5. i have a dell optiplex 170L every time i on it.. the fan start rolling.. but on the front of my desktop the green and orange light are constantly on and my system don’t come up… and all the Diagnostic Lights are off.. what could be the problem?

    1. The diagnostic lights could vary depending on the model Dell you have. I would pull the manual for your computer at the Dell sight. There will be troubleshooting a diagnostic codes for your specific model in that manual.

      1. This was the situation, I was trying to figure out why computer keep shutting down after a few minuds then I figure out it was my bracket to the heat sink needed to be replace. Later I had to unscrew my motherbored to get one screw out where the bracket to the heat sink goes, once I got that done…I put everything back then when I turned it on the monitor wouldn’t come on so I looked at the back of my tower and saw only the “D yellow” light on.

      2. I am currently trying to revive a dell dimension 2400 series we found at a scrap yard but b and c are yellow and the rest a green i have check the manual but it does not list this pattern. I am planning to run linux but this is not a priority i just want to fix a pc Thank You

        1. Any beep codes? You may have to troubleshoot this the old fashioned way: Remove memory, replace one stick at a time…remove any unnecessary cards, maybe swap in a different power supply. If all those pass, then you’re probably looking at a new CPU or motherboard, which means you will be building a new computer, almost. Good luck. Let us know what you find.

  6. Dell Inspiron 4500 no had signal. Was really thinking a failure other then memory, however your explanation of light codes put me right on the faulty installed memory. One of the two existing memory cards failed, upon removal of the faulty memory card the system returned with a signal. Seems the solution relies on removing both and reinstalling the remaining good card. Thanks for posting the light codes even though it was 11 years ago.

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