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Discussion Starter #1
So I just bought an 03 SMT 6 speed last Friday and man is it fun to drive. I bought it from a sketchy new jersey dealer and on my ride home the CEL went on so I used my diagnostic and found p0171 and a p0031. I cleared both codes and the P0171 has remained off since(over 500 miles and about a week) but the P0031 comes back every 30 minutes or so. Also the heat shield for the two pre-cat O-2 sensors(relating to P0031) was inside my spare tire trunk when i bought the car and the O-2 sensors look to be kinda new like they were recently replaced. I'll have to look into this tomorrow when its not raining but I'm starting to worry. I apparently have a 6 month warranty from CARS Protection Plus inc. so i want to get everything fixed but who knows.

What do you think is going on here guys?

Ill make another thread about my SMT problems because I feel as if this is enough for one thread and is not related.

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If you have a 6 month warranty, they have to make sure all CEL codes are corrected and keep on them to fix it. How does the SMT run otherwise? I found this online for you:

P0031 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

OBD-II Trouble Code Technical Description

Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
What does that mean?

A P0031 DTC (diagnostic trouble code) refers to the O2 sensor (oxygen sensor) located on Bank 1 in front 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 compared 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 temperature 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, P0051, and P0052
Potential Symptoms

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
Possible Solutions

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).

All of that indicated, I'd take it back where you got it and make them fix it. I guess the only point of disagreement with this source ^^ is that many here have used non Toyota O2 sensors, saved a lot of money, and they worked well, but since it's under warranty, make them fix it definitively.

Good Luck
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