Testing The Lambda (oxygen) Sensor
Posted 28 December 2007 - 07:51 PM
Obviously, on the mini there are for pins for the lambda sensor.
Someone must know a way to test it! please help!!
Posted 28 December 2007 - 09:54 PM
The engine needs to be at operating temperature.
The Blue/Red and Black wires (loom end)are the sensors heater supply, this is controlled through a relay, witched by the ECU.
The grey and the green/grey wires (loom end) are the sesor signal wires. You need to strip back a little to connect the volt meter. Grey +ve, Green/Grey -ve. Best to use the clip on probes for the multi meter.
With the engine running, you should see the voltage go high to around 500mv and then drop to around 200mv. The time period should be at LEAST once a second (sensor is getting tiered at this point). The voltage numbers are not important as long as they go hi/low.
If the voltage is stuck high, using a hose pipe clamp, gently pinch the fuel supply 'flexi' line (orange), momentaraly, until the engine can be herd to alter tone, too much and the engine will stall. This gives a lean condition and the sensor should read low volts. The lambda sensor is working correctly and the problem lies elsewhere. If the voltage stays high, the sensor may be faulty, or there may be another problem, such as a faulty lambda sensor heater relay.
If the voltage is stuck low, using a hose pipe clamp, gently pinch the fuel return 'flexi' line (green), momentaraly until the engine note can be heard to alter tone, too much and the engine will stall. This gives a rich condition and the the sensor should read high volts. The lambda sensor is working correctly and the problem lies eslewhere. If the sensor voltage stays low the sensor may be faulty.
This method relies on the accuracy of the measuring equipment and the competancy of the person carrying out the work.
The best method to carry out these tests is with a diagnostic unit where the voltage reading that the ECU is using can be seen. This is the most deffinative way do determine the lambda sensor operation.
Posted 04 April 2008 - 05:20 PM
Link to Rover version at MiniSpares
Edited by tmsmini, 04 April 2008 - 05:35 PM.
Posted 04 April 2008 - 05:53 PM
Genuine bosch part number is 0258 003 193
Just make sure they are the correct part number before you take them out of the sealed plastic bag, you will not get a refund if its wrong and the bag has been opened!!
Posted 08 August 2008 - 12:49 PM
Posted 28 June 2013 - 01:29 PM
Sorry to drag this topic up again, have been going over my electrical connections with a magnifying glass, as after I changed my MPI engine loom over, I noticed over twenty places where the insulation near the connections was very poor to nothing as it has had its fair share of diagnostics in the past. Worst places were the TPS, MAP, injector, ECT, IAT and coil pack connectors.
I have also noticed a large knife wound to one of the heater wires of the lambda sensor.
WP_000285.jpg 25.02K 46 downloads
This was hidden inside the black sleeve over the four wires. I am not blaming them, but the last place it went in for diagnostics although many years back was Minispeed. I have now rewired this bit.
Only one thin strand of wire was connected. This is going to effect its operation obviously. But to what degree? On my ACR4 the voltage reading goes from 3.65 to 0.01V. Is this the reason or is it as I think the lambda is screwed.
Edited by zony, 28 June 2013 - 01:29 PM.
Posted 05 September 2013 - 11:40 AM
We too are having issues with a mini.. (sorry to hijack!)
The sensor voltage is reading 1.970 on snapon diagnostics (which is well high!) and shouldn't not be over 1v as thats all a nernst cell can make IIRC.. anyway.. unplugging the sensor and it starts to creep down slowly to 1.900, probably just internal capacitance in the ECU input filter... is this a sensor fault? Mini runs badly with misfires thoughout range.,.
Posted 05 September 2013 - 06:56 PM
Posted 12 January 2014 - 06:24 PM
My Mini MPI has failed the emissions test. the reading from an ACR4 is "O2 VOLTS BNK" 3.97-4.02 at idle. Is the Lambda sensor voltage, and is this the expected reading? Should I take a reading at a higher RPM?
Thanks for your help.
Posted 17 January 2014 - 10:21 AM
The voltage reading is incorrect as you will see from my explanation below.
The lambda sensor on SPi and MPi (Bosch 0258003193) is a 4 wire sensor one. There is a 12w heater element and the cell itself produces a voltage of 0.1 to 0.9v the cell is grounded to the case. It isn't a resistive sensor, there is no voltage fed to it, rather the cell of Zirconium Dioxide produces a voltage in proportion to the oxygen content flowing over it under the right operating conditions.
Sprocket gave the wire colours and functions above. Basically you should check that the 12V supply is coming on via the relay and you could measure the voltage coming out of the sensor using a multimeter when the car is running. At 2000 rpm it should be switching rapidly between the minimum and maximum figures as the MEMS controls the engine conditions.
Most problems with sensors are caused either by deterioration or poor connections, always start from the point of view of making sure the connections are all sound (a good idea for all electrics in a mini anyway
Edited by FlyingScot, 18 January 2014 - 07:30 AM.
Posted 26 January 2014 - 09:35 PM
Thanks for the feed back, and the explanation.
I was fortunate enough to have a spare engine, I have taken the inlet manifold and lambda sensor off them and fitted them to my mini, taken the car for it's MOT and it passed the emissions this time. This means I do not know what was causing the original problem.
The lambda probes were completely different, but both had the wiring as stated previously.
Connecting the ACR4 (The POD I have is 30353200 Iss 2) I am able to compare the figures from pre and post the sensor changes, unfortunately I only took the readings at Idle. The "O2 volts BNK" was similar at about 3.8
The only other differences is the "F/Back BNK1" was off prior to the retest and is now on, and the stepper position is now 58 when it was previously 17.
Does this give a clue to what has failed?
Posted 02 March 2014 - 10:34 AM
I need to get some more readings from MPIs as I am beginning to suspect the later SP software doesn't work in the same way in interpreting lambda readings.
We have had several people reading the MEMS 2J with ACRs getting lambda voltages which are technically impossible and I need to bottom this out by physically measuring the voltage and comparing with the ACR.
Thanks for the info, another piece of the jigsaw
Edited by FlyingScot, 21 January 2015 - 06:55 AM.
Posted 22 August 2015 - 04:05 PM
Hi, using my ACR4 reader on MEMS 2J I am also getting odd readings... mV up to 60 odd for split seconds! but most of the time jumping between 0 and 4.
Flying Scot, if you want more detailed readings let me know!
My mini is a 2001 cooper sport MPI by the way.
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