50 Each issue, in partnership with DiagnoseDan TSB (DDTSB), we’ll give you a real-world diagnostic challenge. Study the evidence, work out what’s really going on and tell us what you think is causing the fault. Get it right and you could earn something money can’t buy: an Aftermarket Troubleshooter mug. Yes, a mug. But not just any mug. These are won, not bought and are only available to winners of the Aftermarket Troubleshooter quiz. So when it appears on your toolbox, desk or tea round, everyone in the workshop will know you’ve earned it. And there’s more than bragging rights at stake. Each issue’s winner will also receive a six-month subscription to the DDTSB technical bulletin database, (www.diagnosedan.com) worth €230 + VAT. The new Aftermarket Magazine troubleshooter quiz In partnership with DiagnoseDan TSB 7KLQN \RX NQRZ \RXU GLDJQRVWLFV" 3XW \RXU IDXOW ᎮQGLQJ VNLOOV WR the test with the Aftermarket Magazine Troubleshooter quiz. The technician finds: O Fault code: P20EE00 – SCR NOx Catalytic Efficiency Below Threshold (Bank 1), stored in the ECM. O Visual inspection shows no physical exhaust damage, external AdBlue leaks or crystallisation around the dosing injector or SCR catalyst converter. O An AdBlue quality check confirms the correct concentration of 32.5% urea. During an initial road test at a steady 80 km/h, live data shows: NOx Sensor 1 (upstream): 45 ppm NOx Sensor 2 (downstream): 72 ppm Under full acceleration: NOx Sensor 1: 854 ppm NOx Sensor 2: 317 ppm Think you’ve cracked it? Enter the Aftermarket Troubleshooter quiz online at tinyurl.com/ATQ1026 Entries for this issue close at 11.59pm on 31 October 2026. We’ll reveal the correct answer on the Aftermarket website shortly after entries close, together with an explanation of the diagnosis. The answer will also appear in the next issue of Aftermarket, and the winner will be contacted by email. Competition terms One entry per person. The competition closes at 11.59pm on 31 October 2026. One winner of an exclusive Aftermarket Troubleshooter mug and a six-month subscription to the DDTSB technical bulletin database worth €230+VAT will be selected at random from all correct entries received before the closing date and contacted using the email address supplied with their entry. No cash alternative is available and prizes are non-transferable. The editor’s decision is final. By entering, entrants agree to their name and/or business name being published in Aftermarket and on the Aftermarket website if selected as the winner. Full competition terms and conditions are available on the Aftermarket website. This issue’s challenge A 2019 Volkswagen Touran 2.0 TDI enters the workshop with the engine management lamp illuminated and an AdBlue system warning message displayed on the instrument cluster. The customer reports that the vehicle drives normally, with no loss of power. Back in the workshop, the technician wants to eliminate a leaking or malfunctioning AdBlue injector as the cause of misleading conversion data. The AdBlue supply line to the dosing valve is temporarily clamped, and an extended overrun (engine braking) road test is carried out. The readings are: NOx Sensor 1 (upstream): 0 ppm NOx Sensor 2 (downstream): fluctuates between 32 and 45 ppm What is the most likely cause? A) Mechanically degraded or poisoned SCR catalyst B) Faulty downstream NOx Sensor 2 over-reading actual ppm C) Faulty upstream NOx Sensor 1 under-reporting actual ppm D) Crystallised or restricted AdBlue dosing injector nozzle
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