Simon Manley

​Why are workshops still in the dark on emissions repair?

Volkswagen Jetta 1.6 BSE 2006

This car failed the emissions test for the NCT in Ireland, and the workshop charged with its repair is stumped. Emissions seems to be a stumbling block for a lot of workshops, and I’m really not sure why.

One reason might be that too many techs try to fix them by ringing someone looking for a silver-bullet answer rather than working through a process. That’s how I came across this job — I got the call.

I don’t mind taking calls like this. In fact, solving complex issues forms the majority of my work, and I thoroughly enjoy it. I like the puzzle, the research, and the challenge. While I can’t give away diagnostic work for free — it’s my livelihood, after all — I’m really happy to talk to other mechanics and try to help them sort out issues. It forms good connections, and it’s good for business in the long run.

What stood out to me on this one was the lack of process. Up to the point of calling me, the extent of the repair effort was clearing the MIL twice right before the test in a sloppy attempt to “get it through.” When I asked basic questions about fuel trims or O2 sensor activity, I was met with complete silence — suggesting live data wasn’t even being evaluated.

The image above is from the fail report sheet after its NCT visit. It shows an incredibly rich running condition both at idle and high idle. So what could be wrong here?

Let’s break it down

First things first: What can cause a rich condition? Broadly speaking, it’s too much fuel, too little air, or fuel vapours unceremoniously entering the intake system.

What if the ECT sensor were faulty? It could be reading -40°C and flooding this engine out.

Another reason — and why I asked what the trims and O2 readings were — is that it could simply be a dead or unresponsive sensor causing the ECU to default rich.

For that matter, it could be as simple as a heavily restricted air filter choking the intake.

I also considered leaking injectors, high fuel pressure, or a heavily worn engine with excess blow-by making its way into the breather system.

Being thousands of miles away and not having hands on the car makes it trickier, but asking the right diagnostic questions usually points you in the direction of logic and data.

Before I could even sink my teeth into a deep dive, one simple question shifted the entire picture: When did it last have an oil change?

A few umms, ahhs, and a quick phone call to the owner revealed the answer: a staggering five years ago.

Yes, you read that right. Five years of unburnt fuel, moisture, and heavy blow-by sitting in the oil, constantly being pulled straight back into the intake through the PCV system and saturating the mixture.

To borrow a phrase from many a mechanic before me: “Well, there’s your problem.“

Final thoughts on this

I’m still awaiting the call back to confirm after they flush it, change the oil and filter, and run it. But given how these calls usually go once the obvious hits… I won’t be holding my breath for a follow-up.

Besides, I know they don’t have a gas analyser so even when this is repaired the real result will only be verified by another visit to the test center.