Oxygen Sensor Heater Test -P0135 (1997-1998 4.2L Ford E150, E250, F150)

Troubleshooting diagnostic trouble code (DTC) P0135: HO2S 11 Circuit Malfunction is not as hard as you might think. The cool thing is that you don't need any expensive diagnostic test equipment... all you'll need is a multimeter.

A trouble code P0135 tells you that the internal oxygen sensor heater for the right front oxygen sensor has a problem. This usually happens when the heater (inside the right front O2 sensor) goes bad.

In this tutorial, I'll show you the 3 basic tests you'll need to perform to diagnose the right front oxygen sensor.

If you need to troubleshoot the left front O2 sensor (HO2S 21), take a look at the following tutorial:

  1. Oxygen Sensor Heater Test -P0151 (1997-1998 4.2L F150, E150, E250).

NOTE: This oxygen sensor is known by several different names:

  1. Right Front Heated Oxygen (O2) Sensor.
  2. HO2S 11.
  3. Right Side Upstream Oxygen (O2) Sensor.
  4. Oxygen Sensor Bank 1 Sensor 1.

Here are the contents of this tutorial:

  1. Circuit Descriptions Of The Upstream Oxygen Sensor.
  2. TEST 1: Verifying The Heater Element Is Getting Power.
  3. TEST 2: Verifying The Heater Element Is Getting Ground.
  4. TEST 3: Testing The Heater Element's Resistance.
  5. Location Of The Oxygen Sensors.
  6. Where To Buy The Oxygen Sensor and Save Some $$$.
  7. More 4.2L Ford Diagnostic Tutorials.

Circuit Descriptions Of The Upstream Oxygen Sensor

Oxygen Sensor Heater Test -P0135 (1997-1998 4.2L Ford E150, E250, F150)

The right front heated oxygen sensor (HO2S 11), on your 4.2L V6 equipped F150 (E150 or E250) is a 4 wire oxygen sensor.

2 wires are for actual oxygen sensing part. The other 2 are to supply the heater with power and ground.

NOTE: You can find the location of the right front oxygen sensor (HO2S 11) here: Location Of The Oxygen Sensors.

Below, you'll find the color of the wires of the engine wiring harness oxygen sensor connector for sensor HO2S 11:

Right Front Oxygen Sensor (HO2S 11) Pinout
(1997-1998 4.2L Ford F150, E150, E250)
Pin Wire Color Description
1 RED/WHT Heater Ground (-)
2 RED Heater Power (+)
3 GRY/RED O2 Signal Ground
4 GRY/LT BLU O2 Signal

TEST 1: Verifying The Heater Element Is Getting Power

Oxygen Sensor Heater Test -P0135 (1997-1998 4.2L Ford E150, E250, F150)

The first order of business is to check that the right front oxygen sensor (HO2S 11) is getting power.

Of the 4 wires sticking out of the engine wiring harness O2 sensor connector... it's the red (RED) wire that feeds power to the HO2S 11 heater element.

CAUTION: The O2 sensor can get and stay very hot! Perform this test with a completely cold engine. Be careful and take all necessary safety precautions! Also, if you raise your vehicle with a jack, place it on jack stands.

IMPORTANT: The illustration of the connector above is of the connector on the oxygen sensor itself. To check for power, you need to test the RED wire of the engine wiring harness sensor connector.

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

  1. 1

    Locate the right front oxygen sensor and disconnect it from its engine wiring harness connector.

  2. 2

    Locate the RED wire of the engine wiring harness oxygen sensor connector.

  3. 3

    With your multimeter in Volts DC mode, probe the RED wire with the red multimeter test lead.

    Ground the black multimeter test lead directly on the battery's negative terminal.

  4. 4

    With the Key On Engine Off (KOEO), the RED wire should have 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: Your multimeter confirms that the RED wire has 10 to 12 Volts DC- This confirms that the right front oxygen sensor's heater element is getting power.

The next step is to make check that the RED/WHT wire, of HO2S 11 engine wiring harness connector, is feeding ground to the heater element. For this test, go to TEST 2: Verifying The Heater Element Is Getting Ground.


CASE 2: Your multimeter confirms that the RED wire DOES NOT have 10 to 12 Volts DC- Re-check that you're testing the correct wire and that the Key is in the RUN position (but don't crank or start the engine) and re-test.

If your multimeter still does not register 10 to 12 Volts DC... then you can conclude that HO2S 11 itself IS NOT BAD... since without power, the heater element won't work.

Although it's beyond the scope of this article... the next step is to find out why this battery power is missing using a wiring diagram.