AWAITING APPROVAL: HJS edging closer to Euro 6 retrofits for London’s TX4 taxis
- Perry Richardson
- 4 minutes ago
- 2 min read
HJS Emission Technology are continuing their push for a new era of cleaner driving for London’s iconic TX4 black cabs. Already in service in cities like Glasgow and Birmingham, the system is now edging closer to adoption in the capital.
In April 2024 HJS confirmed successful completion of initial Euro 6 emissions tests, paving the way for the intensive 10,000‑mile endurance trial that followed. The final emissions approval was tentatively scheduled for January 2025, with a formal rollout to follow.
London’s Transport for London (TfL) work under strict criteria. Retrofit kits for the city must include not only HJS’s selective catalytic reduction (SCR) catalyst, but also a brand new diesel particulate filter (DPF) and a full replacement of the exhaust system. In addition, a 10,000‑mile trial covering two six‑hour Central London shifts was required to demonstrate performance at low urban speeds, typically 10–15 mph.
HJS’s retrofit system is based on proven SCR technology from Germany, using AdBlue dosing to convert upwards of 90% of NOₓ emissions into nitrogen and water. The upgrade integrates with the existing DPF, monitors AdBlue levels, and alerts drivers via a dashboard display. Installation can be completed in a single day, and components meet accreditation under the Clean Vehicle Retrofit Accreditation Scheme (CVRAS) managed by the Energy Saving Trust.
By April 2025, HJS had conducted the final emissions test, with all regulated emissions falling within Euro 6 limits. A defect NOₓ sensor - that TfL did not allow to be changed ahead of the test – resulted in an average ammonia slip at the upper threshold of 10 ppm. London’s project limit is tighter than current Euro 6 or upcoming Euro 7 regulations, both of which do not impose an ammonia slip standard for light vehicles.
Results were submitted to TfL in early May. Pending official approval, HJS could begin retrofitting TX4s across London, offering drivers a clean, practical option to extend their vehicle’s life. The company points to Scotland’s experience: around 100 retrofitted TX4s are in daily operation there, signalling its effectiveness.
