Diagnostic Doctor 17 purge and vent valves, monitor sensor responses, and confirm whether the system seals correctly under command. Then, if required, Hydrocarbon (HC) sniffing can be carried out with a gas analyser such as an MOT emissions analyser in free-running mode, to detect elevated HC at the leak site. Finally, with the leak identified and the necessary repairs carried out, it is important to road-test the vehicle and reproduce the self test conditions that triggered the original DTCs and confirm that no codes return. Not all EVAP issues are caused by leaks, though. In an example involving a Mazda 6 vehicle with the 2.5L engine (14 Sept 2009 – 2 May 2011), a customer reported that the fuel tank would not refill and that the fuel nozzle repeatedly clicked off immediately during refuelling, with no obvious drivability concerns. It turned out that the EVAP canister vent line had become blocked by spider webs and debris inside the hose near the vent valve. This obstruction prevented normal tank ventilation during filling, creating excessive negative pressure inside the tank. The consequences of this type of blockage can include premature pump shut-off during refuelling, the risk of tank deformation or cracking and potential fuel-lean conditions. In fact, this is an issue covered under Mazda safety and emissions recall 7214C. In this example, it required the removal of the EVAP canister and vent hose and the inspection of the vent line for internal blockage. The line needed a thorough cleaning, although in some cases the hose/canister assembly needs to be replaced. Then the proper tank venting and retest refuelling operation could be confirmed before the relevant EVAP system functional tests (e.g., purge valve leak tests) were run to ensure no secondary faults remain. Conclusion A repeatable, structured diagnostic process is essential for solving EVAP faults efficiently and preventing comebacks. Lead with the DMTL pump run test to establish ‘leak/no-leak,’ then use smoke + HC sniff to pinpoint the source and validate with simple electrical checks where needed. Further detail and background on this topic can be found on the Aftermarket website via the link below, where you can also submit your own diagnostic dilemmas for the Diagnostic Doctor to explore. tinyurl.com/DD0726 Everyone wants to get what they paid for. Aftermarket is independently verified by ABC, because we want our advertisers to know they’re getting the exposure they’ve been promised. 17,274 Average Circulation per issue, July 22 - June 23. ABC. See it. Believe it. Trust it. BE WISE WHEN YOU ADVERTISE www.abc.org.uk To advertise call Angela Lyus on 01732 370340 or email angela@aftermarket.co.uk 22,797 Average Circulation per issue, July 2024 to June 2025
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