Has anyone had to change an oxygen sensor on a mk3 MX5. The local garage wants £600 to change both sensors using genuine Mazda parts. I obtained supposedly correct non Mazda parts for a fraction of the OEM parts on line. However looking at the ones on the car the plug ends are reversed. Is this a ploy by Mazda to get you to buy genuine parts at a huge profit. Only option as I see is to cut the cables and use crimps. Not really a good idea given the location of the parts. Any help welcomed.

These sensors changed in mid 1994 as far as I can see no one lists a direct fit replacement for the later cars.
Gendan however list a universal sensor for the application at £24, while universal sensors can be problematic on some applications however Gendan have been specialising in lambda sensor have been selling these sensors for a long time and usually know what they are doing.

One of the problems with universal sensors is the wires to the sensor are aluminium and it can be difficult to get a reliable splice connection.

If you are changing them yourself get a proper O2 sensor wrench it makes the job much easier, also clean the threads out with an 18mm spark plug chaser tap.
Usually the downstream sensor B1S2 never needs changed unless the wiring gets damaged if you have a P0420 fault code it is usually not the downstream lambda sensor to blame.

[Edited on 21/5/16 by britishtrident]

Update interestingly Just lambda ( www.lambdasensor.com ) don't list a sensor for any MX5 other sources list a subsequent change at the Mk3 introduction.

MX5 Parts list them though ?

http://www.mx5parts.co.uk/oxygen-sensor-aftermarket-front-mk3-35-p-2049.html


Don't use crimped terminals if you are using a 'universal' lambda sensor
use solder and heatshrink imho

[Edited on 22/5/16 by perksy]

I managed to get the old sensor out with difficulty. It is well concealed behind the steering column and suspension. I found some grease filled crimps I used to use at BT for jointing. A difficult job to do even In a workshop. Took it for a run and all seems well. Thanks for all your input.

It really is worth getting a low cost scan tool to check these things, they can give a lot of information and give peace of mind with regards to passing the MOT emission test.

A cheap OBD2 scan tool that in addition to reading and clearing fault codes reads (and prefferably graphs) live data and read the I/M readiness monitors is worth it weight in gold.

I/M Readiness Monitors are built in tests used in the USA instead of tail pipe exhaust emission testing, in the USA they are reckoned to be stricter than an MOT style tail pipe test if all tests are shown as complete then the car will almost certainly pass an MOT emission test.show

Live data graphs will how the Lambda sensor and catalyst are working.

This is the output voltage from Upstream and Downstream Lambda sensor after about 2 to 3 minutes running.
The hi-lo pattern shows upstream sensor (blue trace) is workin and the car is running closed loop.
The downstream (post cat) sensor (green trace) is only just starting to warm up and the catalyst is not yet working.


Upstream O2 Sensor After 2 Min

After a few more minutes running the catalyst is hot enough to start working and burn off pollutants.
The voltage output from the post cat sensor has risen and is giving a smooth output importantly not following the hi-lo pattern of the upstream sensor.

Upstream Oxygen Sensor Hot Idl


Sanpping the throttle open and closed in neutral should show something like this.


Upstream O2 Hot Snap Throttle



[Edited on 22/5/16 by britishtrident]