O2 Sensor Heater Tests

As mentioned on the previous page, if you're seeing any one of following DTCs P0135, P0141, P0147, P0155, and P0161 and you replace the oxygen sensor without any further testing... there's a 98% chance that you're ‘hitting the nail on the head’.

But before you run off and replace it, you should check for two very important things so that the odds of solving the diagnostic trouble code or codes are 100%. They are:

  1. That the specific O2 sensor the DTC is accusing as having a heater malfunction does not have its wires shorted and melted together on the exhaust pipe.
    1. When this happens, you can bet that the O2 sensor heater fuse has blown.
    2. This is usually the end result of human error, usually because some component was removed and replaced and the O2 sensor had to be disconnected.
    3. When reconnected, the wiring was not secured to its original routing and the wires ended up rubbing against the exhaust pipe or exhaust manifold.
  2. That 12 Volts are present in at least one of the 4 wires. You need to test for these 12 Volts with a multimeter in Volts DC mode with the Key On (but engine Off).
    1. I suggest testing for this voltage even if the O2 sensor's wires are NOT shorted and melted to the exhaust pipe or exhaust manifold.

Well, to make the long story short, you'll usually see one of the following cases:

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 codes present, because the O2 sensor heater fuse also supplies power to other engine sensors.

With this test result, you'll need to do 2 important things (since an O2 sensor fuse doesn't get blown for no reason):

  1. Check that the O2 sensor's wires and its harness connector wires are not shorted together or shorted to the exhaust pipe and if they are repair them and/or replace the O2 sensor.
  2. Replace the blown fuse and road test the vehicle.
    1. If the fuse does not get blown again, you can consider the problem solved.

After repairing the problem (whether you needed to replace the O2 sensor and/or repair the wiring), road test the vehicle to make sure the O2 sensor heater diagnostic trouble code (DTC) doesn't come back.

Where Are The O2 Sensors Located?

If you're driving a 2.2L, 2.4L, 3.1L, 3.4L, 3.8L equipped vehicle, you only have two oxygen sensors to worry about. These are labeled O2S11 (upstream) and O2S12 (downstream).



If you're driving a vehicle with a 4.3L V6 or a 5.0L, 5.7L V8, then your vehicle will have either 3 or 4 sensors.

Don't panic... the cool thing is that within the description of each DTC, you'll find the info you need to locate the location of the O2 sensor.


If your vehicle has a V6 or V8, you need to know where Bank 1 and Bank 2 are located.

For all engine sizes, you need to know what the terms sensor 1 and sensor 2 mean. Here are the specifics of each diagnostic trouble code (DTC):

  1. P0135 Heated Oxygen Sensor (HO2S11) Heater Circuit Bank 1 Sensor 1.
    1. 2.2L, 2.4L, 3.1L, 3.4, 3.8L:
      1. This is the upstream O2 sensor (before the catalytic converter).
    2. 4.3L:
      1. Bank 1 is the bank that houses cylinders 1, 3, and 5.
      2. This is an upstream O2 sensor (before the catalytic converter).
    3. 5.0L, 5.8L:
      1. Bank 1 is the bank that houses cylinders 1, 3, 5, and 7.
      2. This is an upstream O2 sensor (before the catalytic converter).
  2. P0141 Heated Oxygen Sensor (HO2S11) Heater Circuit Bank 1 Sensor 2.
    1. 2.2L, 2.4L, 3.1L, 3.4, 3.8L:
      1. This is the downstream O2 sensor (after the catalytic converter).
    2. 4.3L:
      1. Bank 1 is the bank that houses cylinders 1, 3, and 5.
      2. This is a downstream O2 sensor (after the catalytic converter).
    3. 5.0L, 5.7L:
      1. Bank 1 is the bank that houses cylinders 1, 3, 5, and 7.
      2. This is a downstream O2 sensor (after the catalytic converter).
  3. P0155 Heated Oxygen Sensor (HO2S11) Heater Circuit Bank 2 Sensor 1.
    1. 2.2L, 2.4L, 3.1L, 3.4, 3.8L:
      1. This is the upstream O2 sensor (before the catalytic converter).
    2. 4.3L:
      1. Bank 2 is the bank that houses cylinders 2, 4, and 6.
      2. This is an upstream O2 sensor (before the catalytic converter).
    3. 5.0L, 5.7L:
      1. Bank 2 is the bank that houses cylinders 2, 4, 6, and 8.
      2. This is an upstream O2 sensor (before the catalytic converter).
  4. P0161 Heated Oxygen Sensor (HO2S11) Heater Circuit Bank 2 Sensor 2.
    1. 2.2L, 2.4L, 3.1L, 3.4, 3.8L:
      1. This is the downstream O2 sensor (after the catalytic converter).
    2. 4.3L:
      1. Bank 2 is the bank that houses cylinders 2, 4, and 6.
      2. This is a downstream O2 sensor (after the catalytic converter).
    3. 5.0L, 5.7L:
      1. Bank 2 is the bank that houses cylinders 2, 4, 6, and 8.
      2. This is a downstream O2 sensor (after the catalytic converter).