It's the time of year for my Traumatic Experience. My elderly but reliable Opel Astra has to undergo its annual mechanical inspection, the ITV, which means taking the car to an official testing station to check on its lights, brakes, suspension, and so on. I view this appointment with fear and loathing – not because I worry that the car might fail, since it's well-maintained, but because every year I fumble the Spanish Language Competence Test involved.

I'm pretty fluent in Spanish, and can discuss the Financial Crisis of the day cheerfully with anyone, be nice to children, even swop jokes in the market. But the ITV reduces me to a stammering wreck. For the language teacher, it is a classic case study in how an unfamiliar environment can shred language competence. Let me specify …

Unfamiliar Vocabulary   How often does anyone, in any language, come across the words 'ease the clutch'? Or 'leave it in neutral' ? Or 'flash your main beam when I say' ? I should be giving you these in Spanish, but I haven't done my revision yet.

Street Slang   The mechanics are all working class lads whose world revolves, I assume, around girls and fiestas and making their motorbike go faster. They surely haven't read the latest thoughtful editorial in El Pais on the Financial Crisis. All the lads understand each other perfectly well, so they don't see why an old grey foreigner can't. Except that the OGF doesn't have years of practice in interpreting catch phrases and in-jokes and the latest funny clichés ...

Multi-channeling   If you work in an ITV, it passes the time to tell your mates about what a great time you had last night – even if they're on the other side of the garage at the time. Don't be distracted by the fact that your mates are simultaneously telling you about that fantastic goal that Messi scored, and about how the Ducati XZ3000 is the fastest pair of wheels in the world - you can always edit in any necessary instructions to clients at random moments.

Absent Grammar   Part of Street Slang is that you don't really bother with grammar, except in a rather cursory, passing way. The ITV lads don't seem to see much point in pronouns. Or tenses, really. Or sentence structure when half a phrase is much less strain ...

Casual Pronunciation   The lads are bored stiff with telling an endless stream of drivers to 'ease the clutch', and so they don't put a great deal of effort into pronouncing the routine phrases. But anyway, outside work, like most people in whatever language, they don't see the use of e-nun-ci-a-ting clearly, when a reasonably formed grunt will do.

Background Noise   To make the tedious routine a bit more tolerable, the lads tune in to a local radio station which does lots of LOUD MUSIC. Inside the echoing hangar of the ITV garage, this sounds like a heavy metal band performing in a scrap yard in full production (or do I mean 'full destruction'?) The result is that the grunts referred to under Casual Pronunciation are not only incomprehensible but inaudible. Which makes aural comprehension tricky.

L1 / L2 / L3 Interference   This being Catalonia, the mechanics switch beween Catalan and Castellano without thinking about it. As a result, every now and then I hear something that sounds vaguely familiar but means absolutely nothing at all. Has my brain imploded due to excessive Background Noise? Has my knowledge of Spanish gone into meltdown, and started to trickle out of my ears? '¿Que? … ¿Que?' I splutter, thus earning an even lower score on the Stupid Client scale.

Faulty Media   The final phase of the test is a killer. You position the car over a pit in the ground for the mechanic to inspect the suspension. After grunting something that begins 'Es MUY importante que …', he disappears and you are left peering at a primitive cheap loudspeaker. Which eventually emits distorted roars and bellows, which mean that you are supposed to … er … do whatever he grunted you to do. I usually twist the steering wheel, stamp on the brake, jump up and down, and this seems to be adequate.

So far, I (and the car) have always passed, which must mean that some sort of communication must have been achieved. I still go into a cold sweat at the thought of the 4th of October.