P0141 Diagnostic -Rear O2 Sensor Heater Tests (2003-2007 2.4L Honda Accord)

When the rear O2 sensor (also known as the downstream or sensor 2) loses its heater function, the PCM responds by setting a P0141 diagnostic trouble code.

Now, an internal heater failure is the most common reason, but it isn't the only condition that can trigger code P0141 on your 2003–2007 2.4L Honda Accord.

In this tutorial, I'll walk you step by step through the process of testing the rear O2 sensor heater circuit with a multimeter. You'll also learn how to verify that the heater is actually receiving both power and Ground from the PCM's control circuit.

By the end of these checks, your results will make it clear whether the P0141 trouble code is being caused by a failed heater element inside the O2 sensor or by a wiring/power supply issue outside of it.

APPLIES TO: This tutorial applies to the following vehicles:

• 2.4L Honda Accord: 2003, 2004, 2005, 2006, 2007.

02 SENSOR CIRCUIT WIRING DIAGRAM:

• O2 Sensors Circuit Wiring Diagram (2003-2007 2.4L Honda Accord).

REAR O2 SENSOR DIAGNOSTICS:

• Rear Oxygen Sensor Performance Tests (2003-2007 2.4L Honda Accord).
• P0137 Diagnostic Tests -Rear O2 Sensor (2003-2007 2.4L Honda Accord).
• P0138 Diagnostic Tests -Rear O2 Sensor (2003-2007 2.4L Honda Accord).
• P0420 Diagnostic -Catalytic Converter Tests (2003-2007 2.4L Honda Accord).

Symptoms Of A Bad Rear O2 Sensor Heater Element

When the rear O2 sensor's heater goes bad, most folks don't notice much in the way of performance problems. This is because the rear sensor doesn't directly control the air/fuel mixture —that's the job of the front air/fuel ratio sensor. Instead, the PCM uses the rear O2 sensor mainly to monitor catalytic converter efficiency.

So what usually happens when the heater element fails? The symptoms are pretty mild. In fact, the most common (and sometimes only) clue you'll get is the check engine light shining nice and bright on the instrument cluster, along with a stored P0141 code.

The only other hassle comes when it's time for emissions/inspection. A non-functioning heater keeps the rear O2 sensor from working, which makes the PCM set a P0141 and turn on the check engine light —automatically causing the vehicle to fail.

A bad rear O2 sensor heater is easy to overlook since the car usually drives "fine". But the illuminated check engine light and stored P0141 code are clear signs the heater element isn't doing its job.

Should I Just Replace The Sensor Without Testing It?

When a P0141 code lights up the check engine light, most folks just go ahead and replace the rear O2 sensor. And truth be told, about 8 times out of 10, that takes care of the problem.

The job itself isn't difficult. Swapping out the sensor can be done in less than 30 minutes, which is why a lot of DIYers take this as their first step. If the new sensor clears the code, great —problem solved.

If it doesn't, many people still see the cost of that sensor as part of the diagnostic process. After all, if they did the work themselves, they've already saved on shop labor (not to mention the diagnostic fee).

If this is the route you want to take, no problem. Below are my two rear O2 sensor recommendations. They're from trusted brands I've been using for years, and I don't hesitate to recommend them:

• Walker Products 350-34122 Oxygen Sensor (Amazon affiliate link).
• Denso 234-4797 Oxygen Sensor (Amazon affiliate link).

That said, I always encourage you to test before replacing. The check is quick, easy, and all you need is a basic multimeter. You'll be making sure the heater element is getting power and Ground from the engine harness connector and that its resistance is within spec.

And like I said, this process isn't complicated. It's something you can absolutely do yourself. So if you're like me and prefer to know for sure that the sensor is really bad before spending the money, I'll walk you step by step through the exact tests in this tutorial.

Circuit Descriptions Of The Rear O2 Sensor

If you've already looked at the rear (downstream) oxygen sensor on your 2003–2007 2.4L Honda Accord, you've seen it uses four wires coming out of its connector.

The sensor's connector itself contains the female terminals, while the engine wiring harness side uses male spade terminals that plug into it.

Out of those four wires, two belong strictly to the internal heater circuit. One delivers battery power (12 Volts), and the other provides the heater's Ground path. If either of these circuits is missing, the PCM will quickly notice and can set a P0141 trouble code.

That's why testing the O2 sensor heater requires knowing exactly what each wire is supposed to do. Here's a quick rundown:

Rear Oxygen Sensor (HO2S 2) Pinout
Pin	Wire Color	Description
1	Green with black stripe (GRN/BLK)	O2 Signal Ground
2	White with red stripe (WHT/RED)	O2 Signal
3	Black with white stripe (BLK/WHT)	Heater Ground (-)
4	Black with red stripe (BLK/RED)	Heater Power (+) 12 Volts

Where To Buy The Oxygen Sensor And Save

If it's time to replace the rear O2 sensor, here are my two go-to recommendations. These come from brands I've trusted for years, and I can confidently suggest them to you without hesitation:

TEST 1: Making Sure The Heater Element Is Getting Power

We'll kick off the diagnostic by making sure the rear O2 sensor's heater circuit is actually receiving 10 to 12 Volts. Without this power feed, the heater element won't function and the PCM will eventually set a P0141 code.

On the 2003–2007 2.4L Honda Accord, the wire that supplies battery voltage to the rear O2 sensor heater is the black with red stripe (BLK/RED) wire.

This BLK/RED wire connects to the male spade terminal identified as number 4 in the connector illustration above.

REAR O2 SENSOR CONNECTOR LOCATION: The rear O2 4-pin connector is inside the cabin, under the front passenger seat, tucked under the carpet along the seat rail area.

CAUTION: The oxygen sensor, catalytic converter, and exhaust piping can get extremely hot and stay hot even after the engine is shut off. Always perform this test with a completely cold engine. When replacing the sensor, use jack stands if you need to lift the vehicle —never rely on a jack alone!

IMPORTANT: You'll be checking for voltage at the rear O2 sensor's engine wiring harness connector (the side with the male terminals), not at the sensor's own connector.

Here are the steps to follow:

1. 1

   Locate the downstream oxygen sensor 4-wire connector and unplug it from the wiring harness connector.
   
   NOTE: The rear O2 4-pin connector is inside the cabin, under the front passenger seat, tucked under the carpet along the seat rail area.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Connect the black multimeter lead to the battery's negative (-) terminal.

4. 4

   Turn the key to the ON position, but don't crank or start the engine.

5. 5

   Probe the male spade terminal that connects to the BLK/RED wire with the red multimeter lead.
   
   I've labeled this terminal with the number 4 in the connector pinout illustration above.

6. 6

   Your multimeter should display 10 to 12 Volts.

Now, let's interpret your results:

CASE 1: The multimeter registered 10 to 12 Volts DC. This is the correct and expected outcome. It tells you the rear O2 sensor's heater is receiving the power it needs. The next step is to confirm the heater is also receiving Ground. For that test, go to: TEST 2: Making Sure The Heater Element Is Getting Ground.

CASE 2: The multimeter DID NOT register 10 to 12 Volts DC. This result confirms the heater isn't receiving power. Without voltage, the heater cannot operate, and the PCM will flag it with a P0141 trouble code.

The most common causes of this missing voltage are gonna be:

• A blown fuse 18 (located in the under-dash fuse/relay box).
• An open-circuit issue in the BLK/RED wire.

Check the O2 sensor fuse, replace it if necessary, and repeat the test. If the fuse is OK, and still no power, your next step is to check the continuity of the BLK/RED wire between the fuse box and the O2 sensor's 4-wire connector.

• O2 Sensor Circuit Wiring Diagram (2003-2007 2.4L Honda Accord).

TEST 2: Making Sure The Heater Element Is Getting Ground

In TEST 1, you confirmed the rear O2 sensor's heater is getting its 10 to 12 Volts of power. Now it's time to make sure the heater circuit is also receiving Ground. Without both power and PCM-provided Ground, the heater won't function, and the PCM will set a P0141 trouble code.

On the 2003–2007 2.4L Honda Accord, the Ground signal for the rear O2 sensor heater does not come from the chassis. Instead, the PCM itself supplies this Ground whenever the ignition key is in the ON or START position. The wire that delivers this Ground is the black with white stripe (BLK/WHT) wire. It connects to the male spade terminal 3 in the illustration above (labeled as number 3).

IMPORTANT: You'll be checking for Ground at the wiring harness connector (the one with male terminals), not at the connector that belongs to the O2 sensor itself.

Follow these steps:

1. 1

   Disconnect the rear O2 sensor from its harness connector.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Connect the red multimeter test lead to the battery's positive (+) terminal.

4. 4

   Probe the male spade terminal that connects to the BLK/WHT wire with the black multimeter lead.
   
   I've labeled this terminal with the number 3 in the connector pinout illustration above.

5. 5

   Turn the key to the ON position (but don't crank the engine).

6. 6

   Your multimeter should now display 10 to 12 Volts if the PCM is providing Ground.

Here's how to interpret your results:

CASE 1: The multimeter registered 10 to 12 Volts DC. Perfect —this confirms the PCM is providing the Ground that the O2 sensor heater needs. With both power and Ground confirmed, the next step is to check the heater element's resistance. Go to: TEST 3: Testing The Heater Element's Resistance.

CASE 2: The multimeter DID NOT register 10 to 12 Volts DC. This result tells you the PCM is not supplying Ground.

Without this PCM supplied Ground, the heater can't operate and the PCM will set code P0141. The most common cause of this missing Ground is an open-circuit in the BLK/WHT wire between the PCM and the connector, or a PCM driver fault (rare but possible).

Your next step is to check the continuity of the BLK/WHT wire between the rear O2 sensor connector and the PCM connector.

• O2 Sensor Circuit Wiring Diagram (2003-2007 2.4L Honda Accord).

TEST 3: Testing The Heater Element's Resistance

At this point, the first two checks have confirmed that:

• The rear O2 sensor's heater element is receiving 10 to 12 Volts DC (TEST 1).
• The rear O2 sensor's heater element is receiving Ground from the PCM (TEST 2).

The last step is to measure the resistance of the heater element itself. On the 2003–2007 Accord, the heater resistance should measure between 5.0 and 6.4 Ohms at room temperature. If the resistance is outside this range, the heater is defective and the PCM will trigger a P0141 trouble code.

NOTE: The rear O2 sensor must be completely cool (ambient temperature) before doing this test. If the engine has been running for any length of time, the rear O2 sensor is too hot or too warm to test. In this case, allow the engine and sensor to cool down fully before checking resistance.

IMPORTANT: This resistance test is done on the O2 sensor's own connector (the side with the female terminals), not on the engine harness connector.

Here's how to check it:

1. 1

   Locate terminals 3 and 4 on the O2 sensor connector itself
   
   NOTE: Remember, you're testing the female terminals of the connector that belongs to the rear O2 sensor itself.

2. 2

   Set your multimeter to Ohms mode.

3. 3

   Measure the resistance across female terminals 3 and 4 using the multimeter test leads.

4. 4

   You should see about 5.0 to 6.4 Ω on your multimeter.
   
   If the heater element is bad, your meter will show one of three things: a short-circuit (0 Ω), an open-circuit (OL), or a resistance reading far above spec (for example, in the thousands of Ohms -which indicates an open-circuit issue).

Now, let's go over the results:

CASE 1: The heater resistance is within 5.0–6.4 Ohms. This is the correct and expected result. It confirms the rear O2 sensor's heater element is in good condition.

In the rare case that the heater checks out but a P0141 keeps coming back, the problem usually lies elsewhere in the circuit —damaged wiring/connector, or in rare cases, a PCM driver issue.

CASE 2: The multimeter showed OL (open-circuit) or resistance outside of specification. This result means the heater element inside the sensor has failed.

Since you've already confirmed power and PCM-supplied Ground in TESTS 1 and 2, you can correctly conclude the rear O2 sensor is defective and needs to be replaced to clear the P0141 code.

When you're ready to replace the rear O2 sensor, below are my two recommendations. They're from trusted brands I've been using for years, and I don't hesitate to recommend them:

• Walker Products 350-34122 Oxygen Sensor (Amazon affiliate link).
• Denso 234-4797 Oxygen Sensor (Amazon affiliate link).

More 2.4L Honda Accord Test Tutorials

You can find a complete list of 2.4L Honda Accord wiring diagrams and diagnostic tutorials in this index:

• 2.4L Honda Accord Index Of Articles.

Here's a sample of the tutorials you'll find there:

• How To Test Misfire Trouble Codes (2003-2006 2.4L Honda Accord).
• How To Test The Engine Compression (2003-2006 2.4L Honda Accord).
• How To Test The Fuel Injectors (2003-2006 2.4L Honda Accord).
• How To Test The Fuel Pump (2003-2007 2.4L Honda Accord).