What Does “OL” Mean on a Multimeter?

What Does “OL” Mean on a Multimeter?

Have you ever been using a multimeter to measure voltage or current and seen a cryptic “OL” appear on the display? If so, you’re not alone – many people encounter this abbreviation and wonder what it means. Let’s shed some light on the mystery of “OL” and decode what your multimeter is trying to tell you.

Decoding the “OL” Message on Your Multimeter

The “OL” reading on a multimeter display has different meanings depending on the type of test being performed. Here are some common scenarios where “OL” may appear:

  1. Testing Continuity: If you are testing for continuity between two points and the multimeter shows “OL”, it means the circuit is open and there is no complete path for current flow. This indicates a broken connection or damaged component.
  2. Testing Voltage: When measuring voltage, “OL” means the input voltage exceeds the selected range on the multimeter. For accurate readings, you need to switch to a higher range to prevent overloading the multimeter.
  3. Testing Current: If “OL” appears when measuring current, it means the circuit current has exceeded the maximum measurable current for the selected range. This is useful when testing high current devices like motors. Select a higher range to get an accurate reading.
  4. Testing Resistance: An “OL” during resistance measurement signifies an open circuit or infinite resistance. It means there is no continuity between the test leads.
  5. Testing Diodes: When performing a diode test, if both leads show “OL”, it indicates an open circuit. There is no connection allowing current to flow through the diode junction for the test.

The Meaning of “OL” Reading

In summary, “OL” generally means an open circuit or out-of-range condition. Understanding the meaning in different test contexts helps to troubleshoot circuits and take accurate multimeter readings. Selecting the right range is key to avoiding overloads.

“OL” Reading Indicates an Open Circuit When Testing Resistance

When testing resistance with a multimeter, an “OL” or overlimit reading signifies an infinite or very high resistance, essentially an open circuit.

This is like a pipe filled with water – the resistance indicates how much water can flow through. A clogged pipe has high resistance and allows little water to pass.

A completely blocked pipe stops water flow entirely, representing infinite resistance. Similarly, OL on a multimeter during a resistance test means no current flows due to an open circuit.

Electron Bot Quote

The analogy comparing electrical resistance to a clogged pipe is a helpful way to understand the concept of an “OL” reading on a multimeter. Just as a clogged pipe restricts water flow, high resistance in an electrical circuit restricts the flow of electrons. When the pipe is completely blocked, no water can pass through it, similar to an “OL” reading indicating no current flow in an open circuit. This analogy simplifies the concept for those less familiar with electronics.

David Lee, RF Engineer, Boston

There are a few things to try if you get an OL reading when testing resistance:

  • Clean the probe tips to ensure a good connection and reduce resistance at the contact points. Dirty or oxidized tips can cause inaccurate and OL readings.
  • Use a different set of probe leads, in case your current leads are faulty.
  • Check for issues in the circuit itself, like a bad component or loose wiring connection, that is causing excessive resistance or an open.
  • Use an amplifier to boost the signal if the resistance is very high but not completely open.

If cleaning the tips and leads does not resolve the OL reading, troubleshooting the circuit is the next step to identify and fix sources of high resistance leading to no current flow.

The Infinite Resistance as It Is Shown on Your Multimeter

Distinguishing Between “OL” and “0” Readings When Measuring Resistance

The “OL” reading stands for “overlimit” and indicates that the multimeter cannot measure a resistance lower than what it is currently detecting. Since the resistance is exceedingly high, the meter displays “OL” rather than attempting to show an extremely large number.

This can occur when measuring very low resistances or if the voltage in the circuit under test is too low.

On the other hand, a “0” reading signifies an open circuit, meaning no connection exists between the two test points. This happens when there are no components connected between the multimeter leads or to an input pin on a microcontroller. Some multimeters may display “L” instead of 0 for open circuits.

For example, connecting the positive lead of a battery directly to ground with nothing else in between will show “OL” on the multimeter. However, inserting resistors into a breadboard between the test leads can change the reading from “OL” to numerical values based on the resistances present. With zero ohms of resistance, the leads would be directly connected, resulting in a “0” reading since there is no resistance impeding current flow.

Electron Bot Quote

In my view, this explanation of “OL” and “0” readings on a multimeter is concise and informative. It clarifies that “OL” means the resistance is too high to measure, typically in cases of very low resistance or low circuit voltage. On the other hand, “0” indicates an open circuit with no resistance. The practical example illustrates how these readings change in real-world scenarios, making it an effective explanation for anyone dealing with electrical measurements.

Kevin Anderson, Control Systems Engineer, Denver

So, “OL” means the resistance is too high to measure while “0” indicates an open circuit with no resistance at all. Checking both conditions helps determine issues in circuits under test.

Difference between “OL” and “0” in Measuring Resistance

Check our useful articles about multimeters:


What does an “OL” reading mean when testing resistance with a multimeter?

An “OL” reading when testing resistance means that the circuit is open and there is no continuity. It indicates very high resistance or an infinite resistance (open circuit).

I’m testing continuity on a circuit and my multimeter shows “OL”. What does this mean?

If you get an “OL” reading when testing for continuity, it means there is a break in the conductive path somewhere in the circuit. There is no complete circuit for current to flow.

When checking diode resistance, my multimeter displays “OL” for both leads. What is causing this?

Both leads showing “OL” during a diode test indicates an open circuit. It means the diode junction is not allowing current to flow between the two probe points. The diode is either damaged or incorrectly connected in the circuit.

Why does my multimeter show “OL” when measuring voltage in a circuit?

An “OL” reading when measuring voltage indicates the voltage is exceeding the selected range on the multimeter. You need to switch to a higher range to get an accurate voltage reading and avoid overloading the multimeter.

What should I do if my multimeter displays “OL” when testing current in a circuit?

If you see an “OL” when measuring current, it means the current is too high for the selected range. Choose a higher range on the multimeter to properly read the overlimit current.

My multimeter reads “OL” when testing a 9V battery. Is the battery dead or is something else going on?

If you see an “OL” reading when testing a 9V battery, the likely issue is that the multimeter range is set too low. Try selecting a higher voltage range like 20V or 50V to get an accurate voltage reading. If it still shows “OL”, then the battery could be dead or have a very low charge.

Under what condition would a multimeter show “OL” when testing for continuity?

A multimeter will display “OL” when testing continuity if there is an open circuit – an incomplete path for current flow due to a faulty connection, damaged wire, bad solder joint, etc. This indicates no continuity between the probe points.

I get an “OL” reading when measuring resistance in a resistor. Does this mean the resistor is shorted?

No, an “OL” reading when testing a resistor means the resistor has very high or infinite resistance, essentially an open circuit. A shorted resistor would show 0 ohms resistance.

My multimeter shows “OL” for all resistance measurements. Is it broken or am I doing something wrong?

It’s likely you are doing something wrong rather than the multimeter being faulty. Most likely causes are dirty probe tips making poor contact or forgetting to turn on continuity/resistance mode on the multimeter before testing.

Why does my multimeter show “OL” instead of displaying a resistance value in ohms?

The “OL” or overlimit reading appears when the resistance in the circuit is higher than the multimeter can measure on the selected range. Choose a higher range or use the auto-ranging feature to allow the multimeter to find the proper range.

I’m testing a circuit and my multimeter flashes “OL”. What should I do to troubleshoot this?

Flashing “OL” means you need to switch to a higher range on the multimeter to accurately read the voltage or current. Start with the highest range and work your way down as needed. Also check connections and inspect components for damage that could be causing excessive resistance.

What causes a multimeter to show “OL” when testing capacitors or inductors?

Large capacitors and inductors can briefly produce an “OL” reading when first connected as they charge. But if “OL” persists, it indicates an open component with internal damage, causing it to act like an open circuit.

My multimeter reads “OL” for resistance on a PCB trace. How do I find the fault?

Check solder joints along the trace for cracks/cold joints. Examine the board for damage like scratches or burnt spots that can create an open circuit. Follow the trace to find any faulty components shorting it.

How can I prevent getting incorrect “OL” readings when using my multimeter?

Make sure your probes have good spring-loaded contact. Clean any dirt/corrosion on tips. Select the appropriate range. Double check that you’re in the right measuring mode. Test known good circuits to verify proper working.

Useful Video: How to Measure Ohms with a Multimeter


Seeing “OL” or “overlimit” on your multimeter display is a common occurrence that has different implications based on what type of measurement you are trying to take.

Most commonly, “OL” signifies an open circuit or very high resistance when testing for continuity, measuring resistance, checking diodes, or testing capacitors/inductors. It means the circuit condition is exceeding the limits of the selected range.

During voltage measurements, “OL” indicates the voltage is too high for the range and you need to switch to a higher range to get an accurate reading.

When measuring current, “OL” means the current is exceeding the maximum amount measurable in the chosen range. Go to a higher range.

“OL” does not necessarily mean the multimeter itself is faulty. More likely, it means there is an issue with connections, damaged components, or incorrect range/mode selection.

Knowing the meaning of “OL” in different contexts will help you troubleshoot and take the right steps to get proper readings. Checking connections, cleaning probes, selecting ranges, and verifying multimeter settings are key to avoiding “OL”.


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