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I've got my MTXL wideband wired to a relay as per the instructions. Power and Ground direct to the battery via relay triggered off a fuse tap on the Wiper fuse so it only turns the MTXL on when key turned to "On". Has been solid wired like this for a long time, unlike the several failures I had when it was just wired direct to an accessory source.

I have been reading the article below which talks a lot about not powering up the sensor before engine start which has got me thinking...

I noticed I tend to turn the key to ignition/on and wait for the pump to finish priming before starting the engine (MTXL is now powered up with engine not running) and often notice the wife will do the same but sometimes leaves the key on ign while she puts her seatbelt on and organises stuff. This could be a minute or 2 or more with the sensor powered up and likely finished it's initial heating process before the engine is started, causing some thermal shock.

So my question: Is it possible to trigger the relay "only" when the key is turned to "Start" but obviously stay on when the key falls back to the "On/IGN" position, but... not trigger when the key is initially turned from "Accessories" to "On/IGN".
Hope that makes sense.

I have a general understanding of electronics but I'm a bit lost on this one

It may be a non issue in the big scheme of things but just want to do things properly.

https://www.nzefi.com/bosch-lsu-wide-band-airfuel-ratio-lambda-sensors-fail-often-aftermarket-performance-applications/

Easiest way would be to use an ECU output to control the relay and only turn it on once engine speed is above say 400rpm and a post start timer has exceeded 4s. This is what I did when I ran a standalong 14point7 wideband and the sensor lasted years and is still going.

Otherwise you might be able to set up a logic circuit using flip-flops or a latching relay to do something similar.

Ohh never thought of ecu outputs. That sounds perfect and I have heaps of outputs available. Thanks, I will look into that!

Wonder how common that thermal shock thing linked actually is?

My MTX-L is wired like that and I almost always turn it on first before starting, waiting for fuel pump to prime.
So mine would get started from cold with a heated sensor almost every time?
And has been for over 10years?

Other than needing a fresh air recalibrate every couple of years it’s been solid. (Hope I don’t jinx myself here!)

From a few years ago:

viewtopic.php?f=55&t=29665&hilit=spartan&start=465