Activate Field Test Mode

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What is Field Test Mode and How to Activate It


It’s often useful to know how strong a signal your iPhone is receiving. If you’re trying to make a call but it won’t go through or if you’re otherwise not getting the cell service you expect, then knowing your signal strength can help you determine why not.

Of course virtually all phones have the “bars” or “dots” graphic that displays on your home screen, supposedly so you know what your cell phone signal strength is.

The problem with relying on those graphical representations for an indication of signal strength is that they are not backed by any standard. That means the accuracy of the dots or bars can vary widely.

Viewing your iPhone’s actual signal strength reading is always preferable to relying on the dots graphic. Signal strength is measured in dBm, or decibel milliwatts, a standard unit of measure.

By viewing the dBm reading on your iPhone you know with certainty how strong a signal you are receiving, and whether the signal needs boosting. To see the dBm you must enter a sequence of commands to put your iPhone into ‘Field Test’ mode and display the reading.

Please note: the iOS 11 update may not allow your iPhone to be placed into Field Test Mode.

How to put your iPhone into Field Test Mode

The following instructions work for iPhone 6 and higher models running iOS 9 or later. As noted above, devices running iOS 11 may be an exception.

To put your iPhone in Field Test Mode:

  • Dial *3001#12345#*
  • Press CALL

For Sprint or Verizon (or any iPhone with the Qualcomm chipset)

  • For all models except iPhoneX, first turn off LTE by going to Settings, then Cellular, then Cellular Data Options.
  • Make sure Enable LTE status is Off. You can turn LTE on again after viewing the dBm reading.
  • Tap on 1x EV-DO
  • The dBm reading is the number identified as Rx AGCO
  • You may have to restart your iPhone to get back into the menu.
  • dBm is typically expressed as a negative number, -88 for example. The closer to zero the reading is, the stronger the cell signal. So a reading of -80 is stronger than -95.

For AT&T or T-Mobile (or any iPhone with the Intel chipset)

  • Tap on LTE
  • Tap 0n Serving Cell Measure
  • The dBm reading is identified as rsrp0.
  • dBm is typically expressed as a negative number, -88 for example. The closer to zero the reading is, the stronger the cell signal. So a reading of -80 is stronger than -95.

Some helpful tips

The LTE signal strength your iPhone displays is not necessarily the same as the 3G or 1x signal strength, since they’re on different frequencies. But the principal is the same – a dBm reading closer to zero represents a stronger signal.

A dBm reading of -50 is about the strongest signal you will see. When a signal is weaker than -100 dBm, that’s a pretty weak signal. If the signal gets much weaker than that, you likely won’t have service.

If you don’t want the dBm reading to display on your iPhone home screen, you can dial the number sequence again and just hit “back to phone” and it’ll return to the dots graphic.

If you need to take dBm readings in several locations – to determine where the strongest cell signal is found, for example – you can put your iPhone into Airplane Mode for a few seconds after taking each reading. Doing this will reset your phone after each reading so the next dBm reading will be accurate.

To access Airplane Mode, swipe the screen from bottom to top. Then tap the airplane icon to turn on Airplane Mode. Wait 5-10 seconds, and then tap the icon again to turn it off.

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