Testing Diagnostic Trouble Codes:
P0135, P0141, P0155, P0161

2 Things to Check When Replacing the O2 Sensor

As I had mentioned in the previous page, DTCs P0135, P0141, P0147, P0155, and P0161 usually indicate that the Oxygen Sensor in question has a BAD internal heater (and replacing the Oxygen Sensor is the solution in 98% of the cases).

Now, while you're replacing the Oxygen Sensor, the diagnostic trouble code indicates is BAD (P0135, P0141, P0155, P0161), I suggest you check for two specific things:

  1. That the O2 Sensor the DTC indicates as having a heater malfunction does not have its wires melted together because they are touching and shorted to the exhaust pipe.
  2. That one of the four wires in the Oxygen Sensor connector has 12 Volts with a Multimeter in Volts DC mode when you turn the Key On (but Engine Off).

CASE 1: O2 Sensor wires are not melted together and 12 volts are present.. then you can replace the O2 Sensor with confidence knowing the Diagnostic Trouble Code will be solved.

CASE 2: O2 Sensor wires are melted together and 12 volts are NOT present, then the O2 Sensor heater fuse is blown.

When the O2 Sensor Heater fuse is blown you'll also see:

  1. Other diagnostic trouble codes present because the O2 Sensor heater fuse also supplies power to other engine sensors.

Where are the O2 Sensors Located?

Within the description of each DTC (P0135, P0141, P0155, P0161), you'll find the location of the O2 Sensor.

But to make sense of the locations, you need to know where Bank 1 and Bank 2 are located.

You also need to know what the terms Sensor 1 and Sensor 2 mean. To help locate the O2 Sensor your specific diagnostic trouble code is pointing to... here are the specifics of each diagnostic trouble code (DTC):

  1. P0135 Heated Oxygen Sensor (HO2S11) Heater Circuit Bank 1 Sensor 1.
    1. Bank 1 is the bank that houses Cylinders 1, 2, 3, and 4.
    2. Sensor 1 means that it's the upstream O2 Sensor (before the catalytic converter).
  2. P0141 Heated Oxygen Sensor (HO2S11) Heater Circuit Bank 1 Sensor 2.
    1. Bank 1 is the bank that houses Cylinders 1, 2, 3, and 4.
    2. Sensor 2 means that it's the downstream O2 Sensor (after the catalytic converter).
  3. P0155 Heated Oxygen Sensor (HO2S11) Heater Circuit Bank 2 Sensor 1.
    1. Bank 2 is the bank that houses Cylinders 5, 6, 7, and 8.
    2. Sensor 1 means that it's the upstream O2 Sensor (before the catalytic converter).
  4. P0161 Heated Oxygen Sensor (HO2S11) Heater Circuit Bank 2 Sensor 2.
    1. Bank 2 is the bank that houses Cylinders 5, 6, 7, and 8.
    2. Sensor 2 means that it's the downstream O2 Sensor (after the catalytic converter).

Where To Buy the O2 Sensors and Save $$$

You could run down to your neighborhood Auto Parts store and buy the Oxygen Sensors you need there, but you'll likely pay twice as much than online.

If you need/want to save some money, you can buy them here:

Upstream
O2S11 & O2S21

Downstream
O2S12 & O2S22

Related Articles

You can find more 4.6L, 5.4L ‘How to Test’ articles here: Ford 4.6L, 5.4L Index of Articles.

Here's a sample of articles you'll find there:

  1. Troubleshooting P0171 and P0174 (Ford 4.6L, 5.4L).
  2. How to Test P0172, P0175 (Fuel Trim Too Rich).
  3. How to Test the Crankshaft Position Sensor (Ford 4.6L, 5.4L).
  4. MAF Sensor Test (at: easyautodiagnostics.com).
  5. EGR System Test (at: easyautodiagnostics.com).

Ford Vehicles:

  • Crown Victoria
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • E150, E250, E350
    • 1997, 1998, 1999, 2000, 2001, 2002
  • Expedition
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009

Ford Vehicles:

  • Explorer (4.6L)
    • 2002, 2003, 2004, 2005
  • F150, F250
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
  • Mustang (GT & Cobra)
    • 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005

Ford Vehicles:

  • Thunderbird
    • 1995, 1996, 1997

Lincoln Vehicles:

  • Aviator
    • 2003, 2004, 2005
  • Mark VIII
    • 1995, 1996, 1997, 1998

Lincoln Vehicles:

  • Navigator
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
  • Town Car
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005

Mercury Vehicles:

  • Cougar
    • 1995, 1996, 1997
  • Grand Marquis
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • Mountaineer (4.6L)
    • 2002, 2003, 2004, 2005

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