Permanent Volt Meter connection to Oxygen sensor ?

[lakemaligne]

I drive a 1996 2Ltr 16v petrol LX, and suspect that the Oxygen (Lamda) sensor may be faulting intermittently,causing my 406 to idle erratically ,ie rev up and down once engine started and then idle at 1200rpm if i engage neutral whilst on the move or it will do the complete opposite and stall if i engage neutral . I would like to monitor the output signal voltage from tne oxygen sensor while the car is on the move to see if the voltage alters at the same time as the car plays up. Would it cause any running problems if i permanently connected a digital volt meter to the oxygen (Lamda)sensor via the harness connector,just behind the engine on the passenger side of the car.

[Gary406]

hmmm i doubt it being the voltage ..

you probably need a new sensor ???

[Doggy]

I've done something similar in the past, but found the results difficult to interpret. The lambda output is never really constant - it's got two states, (effectively rich or lean), one gave, (IIRC), about 0.4V and the other about 1.6V. When idling, the state 'hunts' between the two. You also need to bear in mind that you only have closed loop mixture control under idling and light-load conditons - once you give it any welly, the MAF goes off-scale & the ecu just uses look-up tables to calculate injector dwell, rather than use lambda info.

[lakemaligne]

Hello Dogslife, can you explain what you mean by "closed loop system" please. My car goes like a bomb on the move ,it's once my revs drop to around idle that i get the reving up and down or stalling if i engage neutral .So as long as i get a reading of between 0.4 - 1.6 v while the engine is idling ,it,s in the correct range and the lamda sensor is sending back the correct info to the ECU. What i am basically trying to establish is whether this o/p voltage goes out of range at the very instant or during a fault condition,proving that the lamda sensor is connected with my fault in some way.If it does ,I guess i still dont know whether it's the actual sensor faulting or the exhast gases are going out of range for some reason and the sensor is picking this up,what do you think,am i wasting my time.

[steve_earwig]

It just means everything is tightly monitored to keep emissions down. I can't see why you can't connect a meter to it however I suspect you won't be able to tell if the results you get are the cause of the problem or an effect of the problem.

[Doggy]

If you want to check it a all, I'd be tempted to check it while stationary - just make sure you have this change in output.

As Steve says, if you haven't, you don't know whether it's a faulty sensor of the ecu being unable to control the mixture.

Might be simpler to get a diagnostic check

[lakemaligne]

I will do as you suggest and check the signal output voltage while the car is stationary/idling,but it wont be this weekend as i am up to my neck with decorating the house at the moment. Regarding getting it checked out with a diagnostic checker,to put you in the picture,I have pasted below a section from my previous thread.

I drive a 1996 2Ltr 16v petrol LX with 163,000 miles on the clock,and have just had the ECU replaced with a reconditioned unit to remedy an intermittent idle/stalling issue which I have been trying to fix for 2 years. Before the chap did the swop,he connected his "Network 500" diagnostic equipment and said that all the readings were well within limit and the engine was running very well.However he said that the "Oxygen Sensor" was reacting very slowly ,and said it was lazy and really needed replacing.He also attached his multimeter and said that the signal coming from the oxygen sensor was just outside the recommended parameters. With the new ECU in place the engine started and ran fine ,but the engine fault light was on and his test gear was still showing that the Oxygen sensor was reacting sluggishly and that this could be the cause of my idle/stalling issue at around tickover rpm. He cleared that fault light and since then the engine appears to run fine but the fault light appears once or twice on journeys.

The oxygen sensor was replaced about two years ago in an attempt to cure my fault.

My question is ,what would a lazy Oxygen sensor cause guys.Do you agree with his comments.

[lakemaligne]

Hi Dogslife,I have nearly finished the decorating and was going to see if i could connect up a digital multimeter to the plug connector for the oxygen sensor this weekend,so that i can see if anything happnes to the output signal voltage when the car faults.I will also monitor it as you suggest while its ticking over.
I have 3 questions,
1. If the meter reading does not alter during a fault condition,can i assume that the fault is not being caused by the oxygen sensor circuit,and need to look elsewhere or give up !.

2.When you say ,("I need to bear in mind that I only have closed loop mixture control under idling and light-load conditons - once I give it any welly, the MAF goes off-scale & the ecu just uses look-up tables to calculate injector dwell, rather than use lambda info").does this mean that the oxygen sensor cannot cause any problems once i am say cruising,as the ECU has taken over.

3.When my engine is ticking over,could a faulty oxygen sensor cause the engine to die instantly,with out any other sign,ie revving up and down or uneven tickover,or spluttering ,only my car has started to do this while waiting at traffic lights etc.Its just like i have switched of the ignition.