Testing The Oxygen Sensors (1996-2003 5.2L, 5.9L V8 Dodge Ram Pickup)

With the help of this article, you'll be able to easily test the oxygen sensor on your OBD II equipped V8 Dodge Ram pickup.

Testing them, before replacing them, makes a ton of financial sense since many times the PCM (Powertrain Control Module = Fuel Injection Computer) accuses them as being bad when they aren't. When this happens, you usually have another issue that's confusing the PCM into thinking they're bad.

Your 5.2L, 5.9L V8 Dodge Ram pickup comes equipped with more than one oxygen sensor, this article concentrates on testing the oxygen sensor or sensors that are before the catalytic converter (O2S11 -and O2S21 if equipped).

APPLIES TO: This tutorial applies to the following vehicles:

• Dodge Ram 1500 Pickup 5.2L V8: 1996, 1997, 1998, 1999, 2000, 2001.
• Dodge Ram 2500 Pickup 5.2L V8: 1996, 1997, 1998.
• Dodge Ram 1500 Pickup 5.9L V8: 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003.
• Dodge Ram 2500 Pickup 5.9L V8: 1996, 1997, 1998, 1999, 2000, 2001, 2002.
• Dodge Ram 3500 Pickup 5.9L V8: 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003.

3.9L V6 Dodge Ram Pickup Front O2 Sensor Tests:

• Testing The Front Oxygen Sensor's Performance (1996-2001 3.9L V6 Dodge Ram Pickup)

3.9L V6 Dodge Ram Van Front O2 Sensor Tests:

• Testing The Front Oxygen Sensor's Performance (1996-2003 3.9L V6 Dodge Ram Van)

5.2L, 5.9L V8 Dodge Ram Van Front O2 Sensor Tests:

• Testing The Front Oxygen Sensors (1996-2003 5.2L, 5.9L V8 Dodge Ram Van)

Important Suggestions And Tips

TIP 1 –Use a scan tool with Live Data: You'll need a scan tool with live data capability to use the info in this article.

• It doesn't have to be the Dodge factory tool or a high-end professional model.
• A basic scan tool that shows live sensor readings will do the job.
• Don't have one? Need one? Check out my recommendation: ZM301 OBD2 Scanner Diagnostic Tool (at: amazon.com).

TIP 2 –This is an on-car test: The way I'm gonna' show you to test the oxygen sensors, is with them in place (on the exhaust pipe) and in action, so you don't need to remove them to test them.

TIP 3 –Warm up the engine first: Make sure the engine is fully warmed up before testing.

Even though the O2 sensors have built-in heaters, it's best to run the test once the engine is at normal operating temperature.

TIP 4 –Check for other sensor issues first: Avoid testing if you've got any active trouble codes for other sensors (like MAP, engine coolant temp sensor, etc.).

If something else is wrong, it can throw off the fuel mixture and mess with the O2 sensor readings. Clear those issues first if needed.

Symptoms Of A Bad Oxygen Sensor

The effects of a bad oxygen sensor can be very subtle since they usually do not cause serious drive-ability problems. Here are the most common symptoms:

• Check engine light (CEL) on: The check engine light will be illuminated on your instrument cluster.
• O2 sensor diagnostic trouble codes (DTCs): These are the most common O2 sensor codes you'll see stored in the PCM's memory:
  • P0131: Upstream Heated Oxygen Sensor (O2S11) Circuit Out Of Range Low Voltage (Bank 1).
  • P0133: Upstream Heated Oxygen Sensor (O2S11) Circuit Slow Response (Bank 1).
  • P0151: Upstream Heated Oxygen Sensor (O2S21) Circuit Out Of Range Low Voltage (Bank 2).
  • P0153: Upstream Heated Oxygen Sensor (O2S21) Circuit Slow Response (Bank 2).
• Bad gas mileage: You may find yourself visiting the gas station more often because the PCM can't fine-tune the air/fuel mixture without good O2 sensor data.
• Failed emissions test: If your state requires a smog or emissions test, the vehicle is very likely to fail if the upstream O2 sensors aren't working.
• Sluggish engine performance (sometimes): This doesn't happen in every case, but you may see mild hesitation, rough idle, or slightly slower throttle response —especially if the fuel trim is way off due to a stuck-rich or stuck-lean sensor reading.

Oxygen Sensor Basics

To better understand what exactly you'll be testing, let's go over a quick working theory of how the oxygen sensors function on your 5.2L, or 5.9L Dodge Ram pickup.

Here are some more specifics:

• O2 Sensor Purpose:
  • The oxygen sensor's main job is to help the PCM (Powertrain Control Module) fine-tune how much fuel is injected into the engine.
  • It does this by generating a voltage that changes based on the oxygen content in the exhaust.
  • This voltage usually fluctuates between 0.100 to 0.900 Volts.
  • The PCM reads this voltage to decide if the air/fuel mixture is too rich or too lean.
• Rich Condition Signal:
  • When the PCM injects too much fuel, the exhaust has less oxygen.
  • The O2 sensor detects this and responds with a voltage above 0.500 Volts —often as high as 0.900 or even 1.0 volt.
  • This is the sensor saying: "Hey, we're running rich".
• Lean Condition Signal:
  • When the PCM sees the mixture is rich, it reduces the amount of fuel.
  • As a result, the O2 sensor sees more oxygen in the exhaust and drops its voltage —sometimes as low as 0.050 to 0.100 Volts.
  • Any voltage below 0.500 Volts signals a lean condition.
  • The PCM then responds by adding more fuel to even things out.
• Constant Adjustment Loop:
  • This back-and-forth cycle between:
    • The O2 sensor detecting conditions, and
    • The PCM adjusting fuel injection.
  • Happens continuously as long as the engine is running —assuming all components are working properly.
• How to Observe It:
  • If you have a scan tool with Live Data mode, you can actually watch this process in real time.
  • This is exactly how I'll show you how to test your sensors.
• What a Good Sensor Looks Like:
  • A working O2 sensor constantly switches its voltage between rich and lean.
  • You should see it bouncing up and down several times per second.
  • If the voltage stays stuck —or doesn't move at all — the sensor has likely failed.

If the pre-catalytic converter O2 sensors (called O2S11 and O2S21) fail:

They won't report whether the exhaust is rich or lean,
• And the PCM won't be able to adjust the fuel properly.
• That leads to poor performance, worse gas mileage, and even failed emissions tests.

Where Are O2S11 And O2S21 Located?

NOTE: These front O2 sensors are sometimes referred to by different names depending on who you're talking to or what scan tool you're using:

• "Upstream", "pre-cat", "front", or just "sensor 1".

They all refer to the same general location —the sensor that's mounted before the catalytic converter.

Some Dodge 5.2L and 5.9L pickups have one upstream oxygen sensor, while others have two. This can vary depending on the specific model and engine setup, so it's best to visually inspect your exhaust system to know for sure.

Upstream O2 sensors are located on the exhaust pipe where it connects to the exhaust manifold at the cylinder head —basically, between the exhaust manifold flange and the catalytic converter.

On your scan tool (when it's in Live Data mode), the upstream —or pre-catalytic converter— oxygen sensors are usually labeled as:

• O2S11 –Bank 1 Sensor 1.
• O2S21 –Bank 2 Sensor 1.

O2S11 – Bank 1 Sensor 1:

• On the 5.2L and 5.9L V8 engines:
  • Bank 1 is the side with cylinders 1, 3, 5, and 7.
  • This is the driver side of the van.
  • This is where you'll find O2S11.
• NOTE: If your Dodge was made between 1995 and 1999, this is the only pre-cat oxygen sensor it'll have.

O2S21 – Bank 2 Sensor 1

• On the 5.2L and 5.9L V8 engines:
  • Bank 2 is the side with cylinders 2, 4, 6, and 8.
  • This is the passenger side of the van.
  • O2S21 is located on this side.
• NOTE: If your Dodge is 2000 or newer, it will have both O2S11 and O2S21 installed.

What About the Rear Sensors? Just in case you're wondering: the downstream oxygen sensors (the ones after the catalytic converter) are referred to as:

• O2S12 –Bank 1 Sensor 2.
• O2S22 –Bank 2 Sensor 2.

These rear sensors aren't used for fuel control. They're mostly there to monitor the efficiency of the catalytic converters —so we won't be focusing on them in this tutorial.

TEST 1: Manually Inducing A Rich Condition

To test the oxygen sensors, the very first thing you'll do is to induce a rich condition.

The fastest and easiest way to induce this rich condition is to spray a little carburetor cleaner spray into the engine (while it's running) thru' a vacuum hose (that has engine vacuum).

When the carb cleaner spray is consumed (in the engine cylinder), an instant rich condition will be created. The O2 sensor or sensors will react and produce 0.900 Volts on the scan tool.

Don't have a scan tool? Need a scan tool? Check out my recommendation: ZM301 OBD2 Scanner Diagnostic Tool (at: amazon.com).

Alright, this is what you'll need to do:

1. 1

   Start the engine and let it run for about 15 minutes.

2. 2

   Connect your scan tool and get to its Live Date mode.

3. 3

   Scroll down the list of PID's until you find the ones labeled O2S11 and O2S21.
   
   These show you the voltage output from the upstream sensors.
   
   NOTE: If your Dodge Ram pickup is a 1996–1999 model, you'll only see O2S11. O2S21 only shows up on 2000+ models.

4. 4

   Observe the voltage readings for O2S11 and O2S21 on your scan tool.
   
   With the engine fully warmed up and running normally, you should see the voltages on O2S11 (and O2S21, if present) moving up and down. Expect readings between 0.200 to 0.900 Volts, switching several times per second.
   
   If the voltages seem stuck or not moving, don't worry yet —continue to the next step.

5. 5

   With the engine still running, spray a small burst of carb cleaner into a vacuum hose that has engine vacuum.
   
   If you spray too much and the engine stalls, just restart it and spray less next time.

6. 6

   You should see the voltage numbers for O2S11 and O2S21 spike immediately to around 0.800 to 0.900 Volts.
   
   As long as you're spraying, those voltage numbers should stay high.

7. 7

   Stop spraying and observe the O2S11 and O2S21 numbers.

8. 8

   The O2 sensor values should drop back down.
   
   Within a few seconds, they should start oscillating again between 0.100 and 0.900 Volts.

OK, the test is done, let's take a look at what your test results mean:

CASE 1: The O2S11 and O2S21 voltage readings spiked to 0.900 Volts when you sprayed carb cleaner. So far, this tells you that both upstream oxygen sensors are able to detect a rich air/fuel mixture.

Now, we need to see if the sensors react to a lean air/fuel mixture. Go to: TEST 2: Manually Inducing A Lean Condition

CASE 2: O2S11 did not spike to 0.900 Volts during the test. This confirms that Bank 1 Sensor 1 (O2S11) is no longer responding correctly. You can go ahead and replace this oxygen sensor.

CASE 3: If O2S21 did not spike to 0.900 Volts during the test. This confirms that Bank 2 Sensor 1 (O2S21) has failed. You can go ahead and replace this oxygen sensor.