How To Test a Ford Ranger O2 Sensor

How To Test a Ford Ranger O2 Sensor


There’s more than one Ranger O2 Sensor in your Ford truck, but the most important one is the upstream oxygen sensor. This unit is also known as the primary O2 sensor, and for good reason. It’s the sensor that your Ford engine computer relies on to relay to make the right adjustments to fuel delivery. Today I’ll be showing you how to test the upstream Ranger O2 sensor in a 1997 Ford truck with the 2.3 liter engine in it.

When your truck is running your computer is constantly trying to reach the most efficient air fuel ratio possible. This is called closed loop operation and your Ford truck uses the signal from the upstream oxygen sensor to do it. As you put miles on your Ford Ranger however, this sensor can become fouled or fail all together.

Failure of your Ranger O2 Sensor can result in quite a few Ford truck issues. Some of the more common Ford Ranger problems can include a rough idle, or your truck shifting harshly. If your Ford engine computer sees a value that it doesn’t like from the primary O2 sensor, it will throw your Ranger check engine light on. If you own a 1995 and above Ford Ranger, this means you’ll need a OBDII scan tool to retrieve your trouble code.

Test a Ford Ranger O2 Sensor 1

Your primary Ranger oxygen sensor is located on the passenger side of the vehicle. To reach the harness to your O2 sensor you may need to remove your Ranger mass air flow sensor and the intake tract to your throttle body.

If you suspect your Ranger O2 Sensor as the primary culprit to the problems with your Ford truck, I’ll be showing you how to test the operation using a digital multimeter. Not sure what this is or have no idea how to use one? Check our guide on voltmeters, multimeters and more here.

Ford Ranger issues from a bad front O2 sensor

When your upstream oxygen sensor goes out on your Ford Ranger, your engine computer will lack the ability to adjust the fuel properly. This can cause a variety of problems from annoying to highly dangerous or potentially disastrous. Here’s a few other Ford Ranger problems that are common to this sensor failure below :

  • Bad Gas Mileage
  • Excessively Rich – Too much fuel
  • Catalytic converter failure
  • Inconsistent shift points
  • Check Engine Light ON

When you notice any of these Ford Ranger issues that relate to your front oxygen sensor, you’ll need this guide to test your Ranger O2 sensor. Without the ability to read your exhaust, there’s a good chance your engine will run rich.

Too much fuel means that the excessive hydrocarbons can cause your oil to break down and lose it’s viscosity. Left uncorrected this condition can make your engine bearings prematurely wear and fail.

These hydrocarbons in your exhaust can also burn out your catalytic converter. Either one of these Ford Ranger problems is an expensive repair. To Test your Ford Ranger O2 sensor, we’ll be starting with the power wire.

Testing the Ford Ranger O2 Sensor for Power

You may need to remove the intake tract from your 2.3 liter Ranger engine to reach the front or upstream O2 sensor. Once you’ve located it, disconnect the sensor and then turn the ignition to the “ON” position.

Now that your ignition is turned to the “ON” position, you are sending power to the engine sensors. The first wire you’ll be checking is located at PIN B, remember that you are testing the FEMALE harness or the ENGINE side of the Ranger O2 sensor.

Test a Ford Ranger O2 Sensor 4With the ignition turned to the “ON” position, you should have between 11- 12 volts of power.

If you have power here the next step is to check the ground signal at your upstream Ranger O2 sensor. This is at the female wire of PIN A. Make sure when you are testing the engine harness to never force the multimeter lead into the metal connectors.

Doing so could cause a serious and permanent contact issue. If you don’t want intermittent Ranger O2 sensor issues, you want to gently test the pins in question.

If you have a ground signal at PIN A, then your Ranger O2 sensor should have power and ground needed to function. The next step of this DIY tutorial, you will be measuring the internal resistance of your primary Ranger O2 sensor to see if it’s any good.

Measuring the Ranger O2 sensor internal resistance

The pins you will be measuring now require you to turn the multimeter to the resistance mode. This will allow you to read the internal resistance of your upstream oxygen sensor. This value will let you know whether or not your upstream Ranger O2 sensor has gone bad or not.

Ford Ranger O2 Sensor

You will note that our upstream Ranger O2 sensor wiring diagram shown here is displaying the MALE side or the sensor side.

Probe PIN A and PIN B for the internal resistance. There should be a solid value here, and without a short or an open condition.

If your upstream Ranger O2 sensor is still okay, you will have between 3-27 Ω at these two wires.

Readings upwards of 10 k Ω is a clear sign that your upstream oxygen sensor has died. If this is the case, disconnect the Ranger O2 sensor and remove it. Install a replacement upstream oxygen sensor to correct your engine operation.

Simply use a OBDII scan tool to erase your Ranger check engine code from there. Have any questions about our guide on how to test a Ranger O2 sensor? Leave us a comment below and let us know!