Sooner or later, the rear oxygen sensor's internal heater is gonna' fail. When it does, your Camry's PCM is gonna' light up the check engine light with a P0141 trouble code.
If this is what's happening in your case, this tutorial will help you test the downstream oxygen sensor's heater with a simple multimeter and show you where you can buy it (and save).
Contents of this tutorial at a quick glance:
- Circuit Descriptions of the Downstream Oxygen Sensor.
- TEST 1: Verifying the Heater Element is Getting Power and Ground.
- TEST 2: Testing the Heater Element's Resistance.
- Where to Buy the Oxygen Sensor and Save Some $$$.
You may wondering why in the world would someone put a heater in the O2 sensor when it's already exposed to the exhaust stream's heat. Well, it's due to the fact that:
- The oxygen sensor must reach a temperature of at least 600°F (200°C) to start operating.
- The exhaust cools as it travels down the exhaust pipe and by the time it reaches the rear O2 sensor, it isn't hot enough to heat it up to its operating temperature.
Unfortunately, the O2 sensor's heater doesn't last forever and will eventually fail. Since the rear O2 sensor is a 4 wire sensor, we need to know what two wires feed it with power and ground (to be able to test it). With this in mind, the table below has a brief description of the wires (circuits) we'll be testing.
|Downstream Oxygen Sensor (HO2S 12) Pinout
(1997-2000 2.2L Camry)
|1||PNK/BLK||Heater Ground (-)|
|2||BLK/YEL||Heater Power (+)|
|4||BRN||O2 Signal Ground|
NOTE: I'll be referring to oxygen sensor #2 simply as the rear or downstream oxygen sensor. In case you're wondering, this oxygen sensor is known by several different names:
- Rear Heated Oxygen (O2) Sensor.
- HO2S 1/2.
- Downstream Oxygen (O2) Sensor.
- Oxygen Sensor Bank 1 Sensor 2.
- Post-Catalytic Converter O2 Sensor.
The rear oxygen sensor's heater element needs 12 Volts and ground to start heating the sensor to its operating temperature.
If power or ground are missing, the heater won't heat. So, to get our diagnostic under way, we'll check that the:
- The pink with black stripe (PNK/BLK) wire has ground.
- The black with yellow stripe (BLK/YEL) wire has power (12 Volts).
CAUTION: Perform this test on a completely cold engine and completely cold oxygen sensor. If the engine has been running, let it cool down completely! The O2 sensor and the exhaust pipe (its attached to) stay extremely hot even after engine shut-down.
NOTE: You'll be checking for power and ground on the rear O2 sensor's engine wiring harness connector. The O2 sensor's wiring harness connector has female terminals. The illustration above, is of the connector on the O2 sensor itself (which has male spade terminals).
OK, this is what you'll need to do:
Locate the downstream oxygen sensor and disconnect it from its engine wiring harness connector.
Set your multimeter to Volts DC mode and turn the key On but don't crank or start the engine (this will power up the O2 sensor's engine wiring harness connector).
With your multimeter test leads, probe the female terminals that correspond to the PNK/BLK and BLK/YEL wires of the connector.
Remember, you're testing the engine wiring harness O2 sensor connector (which has female terminals) and not the connector of the O2 sensor itself.
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- Good, since this confirms that the rear oxygen sensor's heater element is getting power and ground.
The next step is to verify that the heater's resistance is within specification. For this test, go to TEST 2: Testing the Heater Element's Resistance.
CASE 2: Your multimeter DID NOT register 10 to 12 Volts DC- The most likely cause is that power is missing due to a blown fuse or a short (or open) in the wiring. You'll need to check the fuse in the fuse box and make sure it's not blown.
If the fuse is OK, your next step is to find out why this battery power (or ground) is missing using a wiring diagram.