P0135 -O2 Sensor Bank 1 Sensor 1 Heater Tests (2001-2004 3.0L V6 Ford Escape)

As you're probably already aware, a trouble code P0135 points to a problem with the internal heater of the bank 1 sensor 1 oxygen sensor (HO2S-11).

In this tutorial, I'm going to explain how to test the HO2S-11 oxygen sensor's heater on the 2001-2004 3.0L Ford Escape (3.0L Mazda Tribute). You'll be able to find out if it's bad or not.

All of the test steps are explained in a step-by-step manner so that you can get to the bottom of the P0135 trouble code lighting up the check engine light on your 3.0L Ford Escape (3.0L Mazda Tribute).

APPLIES TO: This P0135 diagnostic test tutorial applies to the following vehicles:

• 3.0L Ford Escape: 2001, 2002, 2003, 2004.
• 3.0L Mazda Tribute: 2001, 2002, 2003, 2004.

HO2S 11 CIRCUIT WIRING DIAGRAM:

• O2 Sensor Bank 1 Sensor 1 Circuit Wiring Diagram (2001-2004 3.0L V6 Ford Escape).

OTHER 02 HEATER DIAGNOSTIC TESTS:

• P0141 -O2 Sensor Bank 1 Sensor 2 Heater Tests (2001-2004 3.0L V6 Ford Escape).
• P0155 -O2 Sensor Bank 2 Sensor 1 Tests (2001-2004 3.0L Ford Escape).
• P0161 -O2 Sensor Bank 2 Sensor 2 Heater Tests (2001-2004 3.0L V6 Ford Escape).

What Does Trouble Code P0135 Mean?

A P0135: Heated Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) trouble code means that there's a problem with the internal heater of the front oxygen sensor for bank 1.

Although the fuel injection computer doesn't know the exact cause of the oxygen sensor's heater problem, it usually boils down to one of the following:

• The heater itself has failed.
• The O2 sensor's heater is not getting 12 Volts because its power wire has an open-circuit problem.
• The O2 sensor's heater is not getting Ground because its Ground wire has an open-circuit problem.
• The wires that supply 12 Volts and Ground to the O2 sensor's heater have shorted together.

Now, I'm sure you're wondering where oxygen sensor 1 of bank 1 (HO2S-11) is located, it's on the exhaust manifold that faces your Ford Escape's firewall. You can see its location on the exhaust manifold here: Location Of Oxygen Sensor HO2S-11.

Where To Buy The Oxygen Sensor And Save

The HO2S-11 oxygen sensor is known by a lot of names and this can cause a lot of confusion when it's time to purchase a new one. To help you out, here's the original equipment Motorcraft part number: Motorcraft DY877.

The following links will help you to comparison shop and save a few bucks on the HO2S-11 oxygen sensor:

NOTE: If you're not sure if the above upstream O2 sensor fits your particular Ford Escape (Mazda Tribute), don't worry, I researched the part numbers for you and the above O2 sensor's are the replacements for the HO2S-11 oxygen sensor on the 3.0L Ford Escape and 3.0L Mazda Tribute.

Circuit Descriptions Of The HO2S-11 Oxygen Sensor

As you're probably already aware, the HO2S-11 oxygen sensor has 4 wires coming out of its connector.

Two of those four wires connect directly to the oxygen sensor's heater.

To be a bit more specific, one wire supplies the heater with 12 Volts DC and other wire provides it with Ground.

This Ground comes from the fuel injection computer, of your 3.0L Ford Escape (3.0L Mazda Tribute) and is only supplied when the key is in the ON position.

Here's a brief description of the four wires of the oxygen sensor HO2S-11 connector:

O2 Sensor Bank 1 Sensor 1 (2001-2004 3.0L Ford Escape And Mazda Tribute)
Pin	Wire Color	Description
1	LT BLU/ORG	Heater 12 Volts
2	RED/WHT	Heater Ground
3	ORG	O2 Signal Ground
4	GRY/LT BLU	O2 Signal

NOTE: The bank 1 sensor 1 oxygen sensor's engine wiring harness connector has female terminals (see photo 1 of 2 above). The connector on the oxygen sensor itself has male spade terminals (see photo 2 of 2).

You might be asking yourself: Why does the oxygen sensor need a heater? It's because the O2 sensor needs to reach a certain temperature before it activates.

This operating temperature is 600° F and it has to stay at this temperature to be able to sense the oxygen content of the exhaust stream it's exposed to.

If the O2 sensor doesn't stay hot enough, it will stop sensing the oxygen content of the exhaust.

So the only way to be able to maintain the O2 sensor at a constant 600°+ Fahrenheit, is with an internal heater.

The cool thing is is that we can easily check to see if the O2 sensor is getting 12 Volts and Ground. It's also very easy to test the internal heater by doing a simple multimeter resistance test. In this tutorial, I'll show you how.

TEST 1: Making Sure The O2 Sensor's Heater Is Getting 12 Volts

The very first thing that we're going to do is to make sure that the O2 sensor's heater is getting 10 to 12 Volts DC.

These 12 Volts come from the fuse #5 of the Battery Junction Box (underhood fuse/relay box). Fuse #5 is a 15 Amp fuse.

It's the light blue with orange stripe (LT BLU/ORG), of the O2 sensor's 4-wire connector, that carries these 12 Volts from fuse #5 to the heater element of HO2S-11.

The light blue with orange stripe (LT BLU/ORG) connects to the female terminal labeled with the number 1 in the image above.

We're going to do a simple multimeter voltage test to make sure that these 10 to 12 Volts DC are present in this wire.

CAUTION: The oxygen sensor gets and stays very hot even after the engine is off! Perform this test with a completely cold engine. Be careful and take all necessary safety precautions! If you raise your vehicle with a jack, place it on jack stands!

IMPORTANT: To check the presence of 12 Volts, you'll test the oxygen sensor's engine wiring harness connector. This connector has female terminals as shown in the image above.

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

1. 1

   Locate the HO2S-11 oxygen sensor and disconnect it from its engine wiring harness connector.

2. 2

   Set your multimeter to Volts DC mode.

3. 3

   Turn the key ON but don't crank or start the engine (this will power up the O2 sensor's engine wiring harness connector).

4. 4

   Probe the light blue with orange stripe (LT BLU/ORG) wire of O2 sensor's connector with your multimeter's red test lead.
   
   The LT BLU/ORG wire connects to the female terminal labeled with the number 1 (see photo above).

5. 5

   With the Key On Engine Off (KOEO), your multimeter should register 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: Your multimeter registered 10 to 12 Volts DC. This is the correct and expected test result.

The next step is to verify that the O2 sensor's heater is getting Ground. For this test, go to: TEST 2: Making Sure The O2 Sensor's Heater Is Getting Ground.

CASE 2: Your multimeter DID NOT register 10 to 12 Volts DC. The most likely cause of these missing 12 Volts is a blown fuse or a short (or open) in the wiring.

You'll need to check fuse #5 in the underhood fuse/relay box and make sure it's not blown. If it's blown, replace it and repeat the test.

If the fuse is OK, then your next step is to check the continuity of the LT BLU/ORG wire between the fuse box and the O2 sensor connector.

TEST 2: Making Sure The O2 Sensor's Heater Is Getting Ground

So far, you have confirmed that the O2 sensor is getting 10 to 12 Volts on the light blue with orange stripe wire. In this test section, we're going to make sure that the O2 sensor's heater is getting Ground.

The wire that supplies Ground to the HO2S-11 oxygen sensor, of your 3.0L V6 Ford Escape, is the red with white stripe (RED/WHT) wire of its 4-wire connector.

We'll be doing a simple multimeter voltage test, like the one we did in TEST 1, to find out if Ground is present in the RED/WHT wire.

NOTE: To check the presence of Ground, you'll test the oxygen sensor's engine wiring harness connector. This connector has female terminals as shown in the image above.

IMPORTANT: Ground is provided by the fuel injection computer of your Ford Escape (Mazda Tribute). So, be careful and don't short the Ground wire to battery power or you'll fry the fuel injection computer. The multimeter voltage test I'm suggesting below is a safe way of testing for the presence of Ground in this wire.

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

1. 1

   Disconnect the HO2S-11 sensor from its engine wiring harness connector.

2. 2

   Set your multimeter to Volts DC mode and turn the key ON but don't crank or start the engine.

3. 3

   Probe the red with white stripe (RED/WHT) wire of O2 sensor's connector with the black multimeter test lead.
   
   The RED/WHT wire connects to the female terminal labeled with the number 2 (see photo above).

4. 4

   Connect the red multimeter test lead to the battery positive (+) post.

5. 5

   With the Key On Engine Off (KOEO), your multimeter should register 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: Your multimeter registered 10 to 12 Volts DC. This is the correct test result and it confirms that the HO2S-11 sensor's heater element is getting Ground.

The next step is to verify that the heater's resistance is within specification. For this test, go to: TEST 3: Testing The Heater Element's Resistance.

CASE 2: Your multimeter DID NOT register 10 to 12 Volts DC. This test result tells you that the HO2S-11 sensor's heater element is not getting Ground.

The most likely cause of this missing Ground is an open-circuit problem in the Ground wire between the O2 sensor's connector and the fuel injection computer.

TEST 3: Testing The Heater Element's Resistance

Up to this point, you've made sure that the front O2 sensor's heater element is getting both 12 Volts and Ground (TEST 1 and TEST 2).

For our last test, we're gonna' check the resistance the HO2S-11 sensor's heater element.

The internal resistance, of the heater element, should be between 3 to 30 Ohms (at ambient temperature). Yup, the engine can not be hot.

OK, this is what you need to do:

1. 1

   Locate the male terminals labeled with the number 1 and number 2 of the O2 sensor connector itself (not the engine wiring harness O2 connector).
   
   NOTE: This connector has male terminals and belongs to the O2 sensor itself.

2. 2

   Place your multimeter in Ohms mode.

3. 3

   With your multimeter in Ohms mode probe terminals number 1 and number 2 of the O2 sensor's connector.

4. 4

   If all is OK, you should see about 3 to 30 Ohms (Ω) on your multimeter.
   
   If the heater element is fried, your multimeter will show an open (usually indicated by the letters OL) or a number over 10 K Ω.

Let's take a look at your test results:

CASE 1: The oxygen sensor's heater resistance is within specification. This is the correct test result and tells you the oxygen sensor's heater element is OK.

CASE 2: The oxygen sensor's heater resistance IS NOT within specification. This confirms that the HO2S-11 sensor's heater element is fried.

You can conclude the HO2S-11 sensor is bad and the cause of the P0135 trouble code if you have:

• Confirmed that the HO2S-11 sensor's heater element is getting power (TEST 1).
• Confirmed that the HO2S-11 sensor's heater element is getting Ground (TEST 2).
• In this test you have confirmed that the heater element's resistance is not within the indicated specification.

Taking all of the above into account you can correctly conclude that the HO2S-11 sensor needs to be replaced with a new one.

Location Of Oxygen Sensor HO2S-11

The Bank 1 Sensor 1 oxygen sensor (HO2S 11) is located on the exhaust manifold facing the firewall (or in other words, towards the rear of the Ford Escape).

The illustration above is of the exhaust manifold that connects to bank 1 of the engine (bank 1 is the bank for cylinders #1, #3, and #5).

More 3.0L V6 Ford Escape Tutorials

You can find a complete list of tutorials in this index: 3.0L V6 Ford Escape Index Of Articles.

Here's a small sample of the 3.0L Ford Escape tutorials you'll find in the index:

• How To Test The Fuel Pump (2001-2004 3.0L V6 Ford Escape).
• How To Test The Fuel Injectors (2001-2004 3.0L V6 Ford Escape).
• How To Test Engine Compression (2001-2012 3.0L V6 Ford Escape, Mercury Mariner).
• How To Test For A Blown Head Gasket (2001-2012 3.0L V6 Ford Escape, Mercury Mariner).