Failing an MOT is never fun; failing an MOT due to poor emissions performance – and without much of a clue as to why – is even less fun.

Aside from a slight rise in fuel consumption – which I’d put down to the increasingly traffic-jammed route to work – there was nothing to suggest there was anything wrong with the JDMny until it refused to pass the MOT’s emissions testing. With only the test data to go on (there’s no OBD2 as it’s a 1999 model) and a parts catalogue which priced each fuel-and-air-related sensor above £200 I got a sinking feeling – I’d chased a similarly vague issue on my Roadster-Coupé, getting to the bottom of my wallet but never the problem. I didn’t fancy going through that again.

I wasn’t giving up on the little Suzuki just yet though, and decided to take a punt on replacing the o2 sensor as it was the most likely culprit for raised hydrocarbons and lambda, and would be the most affordable too. To bring down the price further it’s worth flexing your google-fu skills and finding which underlying sensor is used in your specific application. Huge numbers of cars will use the same sensor with connectors specific to each vehicle manufacturer or model – I found out which one to get thanks to an eBay listing which had part numbers for Toyota, Honda, Suzuki and many others in a massive list… along with a single Denso part number at the bottom!

The automotive gods were (mostly) on my side when it came to removing the old o2 sensor from the manifold, although the special socket I purchased for the job flexed a lot – after 205,000km I guess the sensor was nicely welded in! It was then just a case of recreating the original harness (keeping the overall length the same) by splicing the connector side of the old harness onto the sensor side of the new one. Happily I happened to have some terminals which matched those in the original Suzuki connector, allowing me to re-pin it (using the slightly different new wiring scheme) for an even neater job.

I got to watch the emissions re-test and the difference in numbers, and lack of red highlights over them, was incredible. Problem solved, thank goodness!