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P0037 O2 Sensor Issue - even with new sensors fitted

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Hi, was just wondering if anybody has come across the issue, I have P0037 on my 2006 SC430 its a pain in the bum, have fitted new (post cat) sensors & still no Joy, can anybody shed any light - all wiring & connectors are fine, these are not really my bag so over to you chaps & chapesses!

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As this related to the heating circuit the error code is normally accurate, i.e. not fooled by something upstream.

Did you replace the sensor with a Denso one that is a direct replacement? Sometimes none OEM/direct replacements parts have a heating element of a slightly different resistance which upsets the ECU.

I assume you changed the correct one?

Otherwise you would need to measure voltages/resistance of the wiring in case there is damage.

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Hi Colin how are you?

Thankyou for your reply - Mmmm? Well these were intermotor ones which my friend got for me @£50 each ( I changed both post cat sensors ) - Right, ok, I will take some readings from both old ones & compare with the new ones ( I suspect it's possible one of the old ones maybe open circuit so will be interesting  to see ) I will let you know how I get on. Where would be best to get denso ones from Colin, any idea?

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Hi Richard, good with me thanks - I hope things are going well for you.

If you replaced both sensors then in theory you should get two error messages if the new sensors aren't quite correct, one for each bank, although these aftermarket sensors can be low tolerance so one could be ok and not the other - you could swap them to see if the error code moves with the sensor or stays with the bank.


From what I can tell the OEM sensor is 89465-24220.

Denso in the UK/Europe only list DOX-0109 as an aftermarket replacement which is a universal fit - so you need to swap over the connector / cut & splice the wiring.

Denso in the US provide 234-4506 which I believe has the correct length wire and plug but they are difficult to get in the UK unless you are going to import from somewhere like


I've purchased Denso aftermarket sensors from in the past. but I'm sure places like and others will stock them too.


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Bingo!!!! So I messed around a bit swapping connections over as you suggested & quickly found by swapping &  deduction that the fault was not one of the sensors at all! 

So I did a diagnostic & interrogated the live data for the O2 sensors & low and behold 000v on bank 1 sensor 2 so i knew then it had no feed so that sent me checking fuses & relays, difficult to get to some of them in the foot-wells but under bonnet ones were easy enough, all fuses were fine??? so then i thought maybe something to do with the ECU?, so i took the three bolts off & removed the cover to reveal the ECU & all the associated cabling etc, I looked to see if i could see any pairs of black wires that looked as though they were together & gave every plug a push & a wiggle - hey presto! Voltage returned - a quick reset & good long drive & I'm a happy fella. Thank you for your assistance Colin - it helped get me on the right track. Fingers crossed! :thumbsup:

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