What does that mean?
A P0031 DTC (diagnostic trouble code
) refers to the O2 sensor (oxygen sensor
located on Bank 1
of the catalytic converter. There is also an oxygen sensor behind the converter
which is Sensor #2.
This O2 sensor #1 may also be refered to as an air/fuel ratio sensor since
on some vehicles it is. It detects the amount of oxygen in the exhaust gas
to the outside air and then vehicle's computer adjusts the air/fuel ratio going
into the engine. The sensor is less effective when the exhaust gas
is low, so it includes a heater which is activated to help get better readings
from the A/F O2 sensor. Essentially this P0031 code means that the resistance
of the heater circuit is lower than normal. In most cases, that resistance level
must fall below 0.8 A to trigger the DTC code.
Note, this code is very similar in nature to P0032
Most likely you'll not notice any symptoms other than the MIL (malfunction
indicator lamp, a.k.a. the check engine
light) will illuminate.
A P0031 DTC trouble code may be caused by one or more of the following:
- A short or open in the heater circuit in the sensor
- A failed O2 sensor heater
- Wiring/connectors broken/frayed leading to sensor and/or relay
- Failed PCM/ECM
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To fix a P0031 DTC code, you'll need to do a proper diagnosis. To do that,
you'll want to inspect the wiring and connectors leading to the sensor. Also
if equipped with a heater relay and fuse, you'll want to check those as well.
Use a digital volt ohm meter to:
- check for 12 volts at the heater circuit feed (hint: unplug the sensor and
check at the wiring connector
to do this measurement)
- check the ground circuit for continuity
- measure the resistance of the heater circuit (done on the sensor itself)
- measure the resistance and voltage of the wiring
Refer to a service manual for the correct specifications (volts, ohms) for
your vehicle. On some Toyota vehicles this code is triggered when the resistance
of the heater circuit is below 0.8 A.
With that said, a common fix for this DTC is to replace the air/fuel (O2 oxygen)
sensor #1 on bank 1.
Please keep in mind that OEM (original equipment) replacement sensors are recommended
(from the dealer). Aftermarket sensors can be less reliable and of poorer quality
(not always, but more often). There's also a chance that replacement parts for
the P0031 code may also fall under a federal emissions warranty (check with
your dealer to see if it's covered).