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Lambda Sensor Problem


alanrichey
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could always tie in with fuel pump, if you did not want it to come on with ignition on

 

Unfortunately the ECU turns on the Fuel Pump for 2-3 seconds when you turn the ignition on and then turns it on when you start to crank, even if she doesn't start. I guess a few seconds for the sensor heater without any gases passing over it wouldn't do any harm, don't actually know how sensitive they are.

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do you know if the heater is supposed to be on permanently when the engine is running?

edit:

http://www.lambdapower.co.uk/diagnosis/diagnostic_index.asp#q10

the heater elements are self-regulating by nature so should stabilise themselves once up to temperature. This is why no independent heater control feedback loop is used

Edited by Grim
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do you know if the heater is supposed to be on permanently when the engine is running?

 

edit:

 

http://www.lambdapower.co.uk/diagnosis/diagnostic_index.asp#q10

 

I read that to say that the 12V supply is permanent and the heating element inside the sensor sorts itself out internally. Hence there are only 2 wires and no extra monitoring wire back to the ECU. Having said that, we have seen that after a couple of minutes the mere presence of exhaust gases will keep the sensor element heated up. So maybe the ECU turns off the heater supply after a couple of minutes ? Don't know.

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I read that to say that the 12V supply is permanent and the heating element inside the sensor sorts itself out internally. Hence there are only 2 wires and no extra monitoring wire back to the ECU. Having said that, we have seen that after a couple of minutes the mere presence of exhaust gases will keep the sensor element heated up. So maybe the ECU turns off the heater supply after a couple of minutes ? Don't know.

Don't forget that the casing of the sensor is usually ground and the sensor generates the voltage that is detected by the ECU. So one wire would be the signal and the other the heater wire. The ECU checks for correct current drain to ensure the heater is within tolerance.

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Don't think that is true in our case. Our sensors are the standard 4 wire type, the 2 White wires are the heater earth and 12V (interchangeable), the Black wire is the sensor earth and the Grey wire is the Sensor signal (0.1V-0.9V) so it doesn't rely on the body acting as earth.

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Don't think that is true in our case. Our sensors are the standard 4 wire type, the 2 White wires are the heater earth and 12V (interchangeable), the Black wire is the sensor earth and the Grey wire is the Sensor signal (0.1V-0.9V) so it doesn't rely on the body acting as earth.

Sorry, thought you were talking about a two wire version. 4 wire version is as you say.. :)

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some info on lamborghini systems here

 

 

Heating process is critical for two reasons: - the osmotic process of exhaust gases is strictly linked to the temperature, and it’s possible only if the tip temperature is over 600°C. So the heater control must measure the tip temperature through the resistance of Vs cell and must keep that temperature close to 785°C (target of the heater control strategy) to ensure the correct efficiency of the sensor.

 

Water condensation on the sensor (when engine is off) and in the exhaust pipes (immediately after cranking) may damage the ceramic components of the sensor, so warm up process is to be controlled to guarantee sensor durability.

 

For heater control, a PWM signal is managed by the LIE 2010 to modulate heating power during cranking and warmed up operation. Heater voltage may be modulated from 4 to 13V during warm up and from 7 to 13V during warmed up operation.

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It would be good if you could observe the heater voltage over a good few minutes to see if it varies. I don't think it will be heating all the time the engine is running. I doubt its PWM but a simple off/on/off/on switching of a clunky old relay dependant on heater resistance feedback to the ecu.

 

Nigel

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OK, we seem to be drifting off-topic a bit here, into our favourite intellectual exercises :) We now know the problem is that the heater is not working properly at start up so my initial problem is solved. To be honest I don't really care if it switches itself on and off while driving as long as it works.

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OK, found more info and not for the first time found I was talking rubbish :)

 

So first, my apologies to Nigel, it turns out it is important. I managed to track down a wiring diagram for the MEMS 1.6 system and it shows that the -ve side of the switching circuit in the sensor heater relay, which we had assumed just went to earth, actually goes back to the ECU. Now there is no feedback loop as such, but apparently when the engine is at full load, working hard, the ECU interrupts the earth line and disables the heater. The book doesn't explain why, so not sure if it just because it is not required, or whether it is to prevent damage to the heater.

 

Still learning :)

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