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Skyvisions, ASE Certified Technician
Category: Toyota
Satisfied Customers: 14465
Experience:  Toyota Master Diagnostic
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Toyota: 2003 toyota camry 4cyl 2.4l p0031 i replaced upstream

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2003 toyota camry 4cyl 2.4l p0031 i replaced upstream 02 sensor.i used a denso sensor.still have same code.

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Do you have a voltmeter and a reasonable knowledge of how to use it? do you have a scan tool or just a code reader?

Customer: replied 5 years ago.
i have solus scanner and voltmeter
With the key in the on position back probe the black wire with a white tracer at the air fuel ratio sensor connector with the connector plugged into the sensor. What is the voltage on this wire? Then with the key in the on position back probe the white wire with the key in the on position and the connector connected what is the voltage on this wire?
Customer: replied 5 years ago.
bl/wht 12v white wire has 3v
The key was on and the engine not running correct? Disconnect the connector and ohm test the sensor on the same or corresponding pins of the sensor as the BW wire and the W wire. Let me know the resistance of the heater element.
Customer: replied 5 years ago.

ok i unplugged sensor messure resistiance between corrosponding wires and i get open curcuit.OL

Your sensor is toast, bad one :-(. The voltage should read 12v on both the wires B/W and W and when you start the car the voltage should drop to 2 to 4 volts then pulse back and for as the computer makes the ground to control the heater element then it eventually settles at about 10v. This will confirm that the computer is not damaged and the integrity of the ground side of the sensor back to the computer. When you have a good sensor recheck this.
Customer: replied 5 years ago.
ok you say voltage should read 12v on both wires key on eng off.i only have 3v on the white..koeo.?
This means there is very high resistance in the sensor heater element. Your meter shows OL but it will probably be in the 100k to 1million range.
Customer: replied 5 years ago.
if you unplug the connecter,i have 12v at the blk/wht and 3 at the wht of the car side.?so the sensor isnt you have the diagram of the wires
This 3 v is a feed back from the computer. The element in the sensor is bad. You confirmed this with the OHM meter. I can not post diagrams on the site. Return the sensor and get another one and ohm test the sensor before you install it.
Customer: replied 5 years ago.
well i went to toyota got a sensor and replaced and same code.Now car is gone for a while,i wont beable to work on it till it comes back.
After installation did you check the voltages on the wires as you did before?
Customer: replied 5 years ago.
yes the voltages are the same.

12 volts and 3 volts or same as 12 volts in and out? Are you on the correct color wires?BLACK/WHITE and WHITE? Did you Ohm test the new sensor?

Customer: replied 5 years ago.

BLK/WHT 12volts WHITE 3volts koeo if you go to sensor wires that line up with BLK/WHT and WHT there is open.did you give me the right colars?

I just checked the diagram. There are 3 possible engine diagrams depending on production dates and PZEV (Partial Zero Emissions Vehicle) . Do you have a VIN available or the production date or the color coding of the four wires at the connector on the harness and I will double check. It is odd that the P0031 is still coming back when the Toyota sensor was installed and there is 12 volts to the heater portion going into the sensor. This means there is a problem with the diagram ie wrong one based on the production of the car you are working on or the line out of the sensor and wire back to the computer is open or the driver in the computer that turns on the ground is bad.
Customer: replied 5 years ago.

vin# XXXXX 08/03 prod date

Is the car available yet? Based on the vehicle identification number this is a late 2003 production date TMMK built Camry. Let's start over. We have to assume at this point that you have a good air fuel ratio sensor from the dealer. But I want to verify or double check that. The information that I gave you on the wiring color code before is not correct. That is partially my fault and I take responsibility for that. However if you have a good air fuel ratio sensor the code for the heater circuit should not be setting. At this point we need to confirm that the voltage is flowing from the EFI main relay to the air fuel ratio sensor and back to the computer. The computer in turn pulses this 12 V to ground on a duty cycle ratio which determines how hot the heater element in the air fuel ratio sensor gets. Then it monitors that current flow to determine whether or not the sensor is being heated up. If it does not see the proper amount of current flow in a given period of time it sets this P0031 code. With the sensor plugged in verify that the color coding of the wires are as follows black with a white tracer, black with a red tracer an orange wire and a white wire. Back probe the black wire with a red tracer with the key in the on position do you have 12 V on this wire? While back probing the black wire with a red tracer start the engine and monitor this voltage. Within 15 or 20 seconds the voltage should drop to near 1 V then slowly work its way back up to about 10 V. Let me know what happens to this 12 V signal on the black wire with a red tracer once the engine is started.

Customer: replied 5 years ago.
ok back at this BLK/Red wire 12v KOEO KOER power starts to go down to about 4volts then went to bat voltage 13.6
Do you have an oscilloscope or a duty cycle voltmeter?
Customer: replied 5 years ago.



The voltage should go to 1-2 volts for a minute or 2 the
voltage is duty cycled to ground by the computer. This can be monitored on a
scope or voltmeter that does percentages or duty cycle abilities. After a
minute or 2 the voltage will slowly work its way up to about 10 volts. 13 volts
means the is no more duty cycle or on time being done by the computer. The
sensor heater is fine. I have seen a few computers get damaged when the sensor
heater fails but this normally keeps the computer from turning the heater on at
all. Yours is turning on initially but is not maintaining it. The only option
is that there is a loose pin fit at the computer or the sensor or the wire
between the 2 there is no other connector involved. Ohm test the B/R from the
sensor to the computer connector pin for as seen below. IF the pin fits are
tight and the wire is good the issue is in the computer.

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