Lambda sensor failure failsafe?

[K4Tuning]

Hey all this question has no specific vehicle relation but is there a proper way to set up the map in the case of a lambda sensor failure? I had this question asked to me and decided to post it to see what everyone thinks. Vehicle was on track and the lambda sensor died. The owner said he felt a loss of power. I would assume if the map was tuned proper, then even without the sensor, the ecu would run off the tuned fuel map correct? Or is there another or better way to set something up in the case of a lambda sensor failure to where the vehicle would run safely without a loss of power to finish a race? Thanks for any info!

[Confused]

The biggest question is... how do you define "failure"...

 

The sensor could "fail" in a number of ways - it could start reading false lean, but still within range. It could be reading false rich, but still within range. Depending on the controller, it could fail and output 0v or 5v, which for some controllers is also the values they use for "full rich" and "full lean", so you can't turn on the voltage input range protection in the ECU if this is the case, as these voltages are also legitimate ones they could use, such as when off-throttle and Overrun Fuel Cut is on - it'll read full lean.

You'll have more in depth error reporting if you're using a Link CAN Lambda, or on-board controller on the Fury, than if you're using one which only has the single analogue output, so in this situation some failures will be reported back and the ECU will stop using that value.

 

What do you have set up as your min/max allowable trims? What do you have as min/max MAP/TPS/RPM ranges for your Closed Loop Lambda?

 

Is the ECU correctly tuned to not require the lambda feedback, or has a tune been thrown together and it's been relying on the CLL to fix the poor tune?

In theory - yeah, once it's tuned, it should run without requiring the sensor, and indeed in many situations - boost, high RPM etc - it'll not be using CLL anyway.

[K4Tuning]

Thanks for the input. I dont know the specifics of the vehicle, if its using Link CAN Lambda or a different wideband. I also dont know anything about the tune or the vehicle, just was asked if there was a way to set up a fail safe in the case of a sensor failure. In regards to your response, The owner did mention the sensor read full lean, so I assume the ecu maxed the positive fuel trim in order to try and correct the matter. Ill let him know your response  thanks again. 

[Vaughan]

If the lambda value goes outside a certain range then CLL will automatically stop working, if you are using an analog input then if that input goes into fault CLL will stop working. Anything else would be tune dependant.

[K4Tuning]

Thankyou for the input, that all makes sense, simple. Im thinking his ultimate fix is to check all settings and tighten up the tune so that if he ever has another sensor failure the map is where it needs to be and vehicle performance shouldnt be effected as much. Thanks again.

[Confused]

Yeah, that's good, but also come back to us with more details, and the advice can get more targeted

[K4Tuning]

Thanks I appreciate it! I dont have much information on the car, owner or the tune. Its a BMW and the question was asked to me because im the most familiar with tuning link in our shop. Theres always more to learn but the vehicle was not tunes though us and iv never encountered that situation. I appreciate all info given. I love the helpful link community!