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.