How To Diagnose And Resolve DTC P0135 (1997-2000 4.2L V6 Ford E150, E250)

TEST 2: Making Sure The Heater Element Is Getting Ground

In this test section, we'll check that O2 sensor's heater element is getting Ground from the PCM when the key is turned to the RUN position.

The wire that delivers Ground to the O2 sensor's heater element is the red with white stripe (RED/WHT) wire of the sensor's 4-wire engine wiring harness connector.

Let's get started:

1. 1

   Disconnect the O2 sensor from its engine wiring harness connector.

2. 2

   Place your multimeter in Volts DC.

3. 3

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

4. 4

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

5. 5

   Gently probe the female terminal of the connector that connects to the RED/WHT wire with the black multimeter test lead.
   
   NOTE: This test is done on the O2 sensor's 4-wire engine wiring harness connector. This connector has female terminals.

6. 6

   Your multimeter should register 10 to 12 Volts DC if Ground is present.

Let's interpret your test result:

CASE 1: The RED/WHT wire is delivering Ground. This is the correct and expected test result.

Your next step is check that the heater element is getting Ground. Go to: TEST 3: Testing The Heater Element's Resistance.

CASE 2: The RED/WHT wire IS NOT delivering 10 to 12 Volts. Without this Ground, the heater element will not function.

The most likely cause of this missing Ground is an open-circuit problem in the RED/WHT wire between the O2 sensor connector and the PCM. Your next step is to find out why this Ground is missing and resolve the issue.

TEST 3: Testing The Heater Element's Resistance

Up to this point, you have:

• Confirmed the O2 sensor's heater element is getting 10 to 12 Volts (TEST 1).
• Confirmed the O2 sensor's heater element is getting Ground (TEST 2).

In this last test section, we'll check the resistance the oxygen sensor's heater element with our multimeter in Ohms mode.

If the O2 sensor's heater element is OK, your multimeter should register an Ohms value between 3 to 30 Ohms (at ambient temperature).

NOTE: This test is done on the connector of the oxygen sensor itself. This connector has round male terminals.

OK, these are the test steps:

1. 1

   Disconnect the O2 sensor.

2. 2

   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.

3. 3

   Place your multimeter in Ohms mode.

4. 4

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

5. 5

   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 sensor's heater element is getting power (TEST 1).
• Confirmed that the 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 sensor needs to be replaced with a new one.

More 4.2L Ford E150 And E250 Test Tutorials

If this tutorial was helpful, be sure and take a look at all of the 4.2L V6 E150 and E250 diagnostic tutorials and wiring diagrams in this index:

• 4.2L Ford E150 And E250 Index of Articles.

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

• How To Test The Throttle Position Sensor (1997-2000 4.2L V6 Ford E150, E250).
• How To Test Engine Compression (1997-2003 4.2L V6 Ford E150, E250).
• How To Test The Fuel Pump (1997-2000 4.2L V6 Ford E150, E250).
• How To Test The CKP Sensor With A Multimeter (1997-2003 4.2L V6 Ford E150, E250).