Use Dell Diagnostic Lights To Troubleshoot Your PC

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.

Category: Dell

About the Author ()

David is a tech professional with over fifteen years of experience in the IT fields of hardware, software and system administration.

Comments (25)

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  1. abdessamad bado says:

    dear sir

    my problem ihave a pc dell but does not work there is a light yellow in it and A-B are yellow also so please i need help.thank you

  2. Dionna says:

    well i saw the d was yellow and delayed going green. what does that mean? all the rest went straight to green and the pc doesn’t boot

  3. steve doebel says:

    added more memory to my computer and got a-c green /b-d yellow what could this be.

  4. Matt says:

    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

    • 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.

  5. Elizabeth says:

    What if A, B, and C are green and D is yellow?

  6. Royce Moss says:

    I have a Dell computer prob 8-10 years old. Its been working fine except for viriuses 2 times that were removed by dell. Suddenly after copying many photo cd’s, when I try to copy photos to a cd I get either no disk in drive and no writetable disk in drive or disk is full. I even downloaded cd burning software and it says basically the same thing. Tired of paying Dell to help.Can anyone help please that don’t cost money. Because the next money I spend will be a newand better computer. Thanks

    • Dave says:

      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.

  7. Kumar says:

    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 ?

  8. lisa says:

    what does it mean if the D light is orange???? all other lights r green

    • Dave says:

      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.

  9. solihin says:

    I have CPU Dell 170L ,the lamp indicator A-B-C-D off but lamp of power is on green ,what happen with my mainboard ?

  10. ernest says:

    I have a dell machine,..AB are yellow and CD arr green and it cant display on the monitor what could be the problem,please help

    • Dave says:

      You will need to lookup the manual for your specific model on the dell website to find out what those codes mean.

  11. Marcus says:

    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.

  12. Sam says:

    I have a Dell tower and A is green and BCD is yellow and I’m trying to get the monitor screen to come on. I need help

  13. Chance says:

    I have a dell computer and the d light is green but all the others are black not yellow or green.

  14. Eazy says:

    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?

  15. Abe says:

    What’s wrong when just the D light is yellow and all others are not on?

    • Dave says:

      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.

      • Abe says:

        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.

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