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Mpi Lambda Sensor/ Emissions

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#1 Norris73


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Posted 03 August 2019 - 06:31 PM

Hi All,


Im in the process of getting my Sisters Mini ready for the yearly nightmare (MOT). Every year the emissions test is a complete nightmare. To that end I have recently purchased a Sykes ACR4 code reader and rover pod 4, this has identified faults with the coolant temp and intake temp sensors, which I have now replaced and the car seems to be running a fair bit smoother.


When viewing values in the component section the O2 sensor voltage seems fairly stuck, on a reading of 1.94v if you rev the car fairly hard to around 3000rpm the reading will jump to 2.12 or so volts and then shoot back down to 1.94v and remain. Im fairly competent with electronics (dabble with valve electronics in my spare time), I have followed Spockets excellent post on O2 sensors and have conducted the following tests:


  • Measured relay O2 sensor heater voltage - 13.95v with engine running
  • Measured O2 sensor data pins (unpluged from loom) - constant 560mV (engine hot and fan on)
  • Fitted old O2 sensor (loose on top of engine) - ACR4 showed 1.5v on engine start but fluctuating and dropped to 0.2v after less than a minute (fluctuating)
  • Measured old O2 sensor data pins with multimeter - voltage jumping between approx 120mV and 650mV (engine hot and fan on)
  • Measured black ground wire on O2 sensor loom plug to ground resistance - 17.5 Ohms (not ideal), however underload heater voltage holds up at 13.7v with engine running and O2 sensor connected (confirmed old O2 sensors tip got very (burning hot).
  • Carried out O2 sensor heater relay test on ACR4 - relay heared to be clicking
  • Found loose connection on ECU (black/front connector), unplugged/removed ecu. Removed orange rubber seal from connector cleaned out crude from underneth, refitted rubber seal and reaseated plug into ECU (which now clicks and latches in correctly)

I have tried to be fairly methodical as above.

The O2 sensor was replaced for last years MOT (a Minispares part), however from my tests Im fairly confident that the fault lies with the Minispares O2 sensor. What are people’s thoughts on this, from my testing above am I jumping to conclsions blaming the O2 sensor. If the general consensus is to replace this I will be after a Bosch part as I can’t trust the Minispares one again.









#2 cian


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Posted 03 August 2019 - 08:43 PM

I have seen this a few times, a genuine Bosch sensor is the only way to go, the aftermarket sensors seem to hold on 1.94 volts or there abouts and do not fluctuate as they should

#3 Norris73


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Posted 07 August 2019 - 02:56 PM

Just a little update to this. I have now fitted a genuine Bosch part no: 0258003193 lambda sensor, the difference is staggering! Before when the Minispares lambda was fitted the reading at idle was a constant 1.94v. Now at idle the reading fluctuates very quickly from approx. 0.2 to 1.4v approx., when reved to 3000+rpm this peaks at approx. 3.5v.

The whole tone of the engine is very different and the exhaust no longer smells of unburnt fuel, the engine revs much more freely, and the idle is very smooth at approx. 900rpm. What is interesting is with the ignition on but engine not running the reading is always 1.94v (as if this is a default reading, and the Minispares lambda wasn’t generating a voltage at all!)


My question if anyone from Minispares is reading this is, if you are unable to source Bosch lambda sensors wouldn’t it not be better to not sell Lambda sensors at all?


If anyone is trying to source a genuine lambda sensor - I got mine from Car Parts in Motion on eBay for £45 -  I have used this company for a number of years to keep my 21 year old Toyota Celica daily driver going with hard to find parts.


I will update with MOT result on Friday.


Hope this helps,



Edited by Norris73, 07 August 2019 - 02:57 PM.

#4 Norris73


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Posted 09 August 2019 - 08:27 PM

Final update to this. Took the Mini in for its MOT today = clean pass with no advisories.


What I have learned from this - Never use aftermarket non OEM spec parts, and don’t always presume that because a part is from Minispares it will be 100%. Always use the genuine Bosch lambda sensor on injected Minis. Also having access to an ACR4 with appropriate pods is invaluable when working on fuel injected Minis.


Other things to check that I have done to ensure it passed emissions, replaced both Coolant and Inlet temp sensors (faults listed by ACR), also check you have a thermostat fitted, this Mini did not, replacing it with a new 88c has also helped no end.


Hope this thread helps people in a similar position with MPI mini emission issues at MOT time.



#5 pete l

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Posted 13 August 2019 - 02:46 PM

I wasted money on a minispares one too. buy cheap, buy twice.


I don't think minispares test everything they sell, they can't do, otherwise this lambda would not be for sale.

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