Testing Your Lambda Sensor

[JohnTurbo]

Well I think i've put a 480 through mot 6 times now, and only three of those were passes for emissions first try, and the other three were very close to fail. My 440 nearly failed too.

The cause for this, has been in all but one case a faulty lambda sensor.

Symptoms that have vanished with a replacement sensor on my 480s:-
* Engine Stutter
* 1200 RPM Idle
* Poor Economy
* Bad CO and/or HC readings

Funnily enough my "lambda" has always been ok for MOT, so don't think because your car has a lambda of 1, that the sensor is ok.

Prior to the sensor failing totally, an inpingement of the inner sensor surface leads to them being "slugish". This negatively affects the function and economy of your car.

After YET ANOTHER emisions fail, for what i previously put down to a cracked element in my cat, i decided to look into how to test these sensors.

The 480 has a 3 wire type lambda sensor (of type Bosch LS2)
At the connection to the wiring loom of the car, it can be seen that there is a two pin plug and a separate spade connector. The two wires are for the heated tip of the sensor, and the spade is the signal wire. Signal ground is via the exhaust system.

Its just possible someone has fitted a 4 wire sensor to your car - as is the case with my 440, so thats whats going on if you find 4 wires.

A lambda sensor typically will only funtion properly for 50000 miles. For this reason, its not rediculous to view them as a service item, much like the cambelt.

Ok, So whats required?
-Just a simple multimeter set to the DC 2V scale, and possibly a socket set to remove the battery tray.

METHOD:-
1) Open bonnet, and locate the connectors to the lambda sensor. These will be either around the area of the abs unit or around the area of the battery tray. If in doubt trace the cable back from the sensor, located on the CAT. It might be that you have to remove the battery tray to find these.
2) The wiring consists of a black 2 pin conector and a spade connector with a rubber sleeve, and a bright green wire.
3) Disconnect the spade/green wire, slide back the rubber sleeve, then reconnect so that the metal is exposed.
4) turn on the multimeter, set it to DC, 2V, connect 1 lead to the spade connector, and the other lead to the battery negative.
5) Start and warm up the car - you may ahve to reconnect the battery, if you reconnected it.
6) After 5 mins of running, observe the reading on the meter.

With the engine idling, a correctly functioning sensor should be switching from 0.8v to 0.2v and back, at a rate of about 1 per second.

A fixed 0.8 volt reading
- Car running rich, probably due to some other reason on the car, such as the MAF being set incorrectly. Dan had this problem. BTW, 0.8v equates to a lambda reading of 0.97 on an MOT.

A fixed 0.2v reading
- Sensor is probably dead, but also an air leak in the exahaust, upstream of the sensor is possible.

If the reading fluctuates, but goes beyond, or nowhere near 0.8v or 0.2v, the sensor is dead or dieing. For example, a sensor that goes from 0.7 to 0.3v and back has become sluggish. A sensor which goes from 0.1v to 0.7v and back is proably inpinged with contaminants.

If the sensor gives a constant voltage which doesn't or hardly fluctuates, between 0.2 and 0.8v - its dead.

I hope this is of some use!

[JohnTurbo]

For the record, this is bang on true for 1.7 and 2.0 models....for turbos don't be too surprised if the fluctuation is about 0.1v around the 0.6v mark.

[JohnTurbo]

For Discussion, please see:-

http://volvo480.dragons.org.uk/forum/vi ... hp?t=15345

[JohnTurbo]

Note:- If you change a lambda sensor, reset the ECU by unplugging the battery for a few mins.

I remember my idle too high mot fail - i was disappointed after changing the sensor to see no improvement. - Then i reset the ecu, and all was well.