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Oxygen isn’t just for humans

The Q5 rolled into the driveway stopping with the bumper about an inch off the roller door. Normally I would applaud this level of skill – but since it was only 7.30am on a Monday and I was in the process of opening for the day, I was less than impressed.

The customer was a drop in – though recommended by another workshop in our local area. Again, I welcome new customers, especially those owning something from the VAG range. I said good morning – and asked if we could move the AUDI so I could continue setting up – and I would be out to discuss asap.

The customer obliged with my request, handed me the keys, and headed down the street to come back when I was ready to roll.

Half an hour later my techs were starting their first jobs for the day, so I thought I’d wander back out to look for the Q5’s owner and find out what the concern was. I arrived at the AUDI at the same time as the customer, returning from a trip to our local café holding a large steaming cup of coffee out in front – a truce gesture no doubt.

Well, for anybody that knows me understands that this is the way to my diagnostic good side – (obviously the customer had been primed by the previous workshop.) The customer informed me that the engine light was on, and the vehicle was in reduced power mode – the instrument cluster had these exact words displayed.

A quick scan later revealed a P0400 fault code recorded in the engine control module. This is a fairly common code for a V6 turbo diesel Audi and generally means the EGR valve is blocked with carbon. Sometimes the valve can be cleaned easily – sometimes it’s more economical to replace the valve.

Removing the metal feed pipe revealed a blockage – but this one was bad! I couldn’t even push a screwdriver into the carbon – it resembled a bag of rapid-set concrete left out in the weather for a few weeks.

I let the customer know that this would not be a simple repair and she should head somewhere other than here – I was in for a busy morning. With contact details recorded and an authority to begin work signed, I rolled up my sleeves and got to it.

Did I mention this one was bad?

With the intake manifold removed, access to the EGR and cooler was possible. It also gave me some access to each cylinder head and its respective intake ports. These weren’t completely blocked but it left me wondering how this engine was breathing!

The Intake manifold fared no better – but this would require some industrial sized cleaning. As I alluded to earlier, the EGR cooler and EGR valve were concrete solid – replacement here I’m afraid.

Calling in a favour from the local TAFE college saw the intake manifold undergo a 12 hour clean in their new state of the art ultrasonic bath – leaving me to deal with the cylinder heads using a more conventional carbon softening and removal agent. 

Beware those that have not attempted this fix – make sure each cylinder is at TDC compression stroke before spraying anything in the ports. You do not want any dissolved carbon or cleaner sitting in the combustion chambers for the eventual start-up – this may cause a hydraulic lock of that cylinder or may cause an uncontrolled run-on.

Assembly the following day went very smooth – the cylinder heads were spotless; the ultrasonic cleaning of the intake manifold worked a treat – it looked like a new part – and the replacement EGR cooler and valve went in.

Despite what most people say about these vehicles, I enjoy working on them, the replacement parts fit well, and it is generally very obvious where each bolt, hose and electrical connector go. I imagine this is what working on a new Honda must be like!

With the cooling system bled, the engine started. Having cleared the fault codes, it was time for a road test.

Did I mention I like these vehicles? Well, it’s hard not to when you drive one. The Q5 is reasonably light and when fitted with the turbo V6 it accelerates like a train! This one did not disappoint. It drove like an AUDI should. Fast, quiet and comfortable.

The owner picked up the vehicle that afternoon with a promise to let me know how it went. I had a phone call about half an hour later – “Its never gone that well, I’ve owned it for years!”

All we did was let the car breathe – no modifications, no tuning, just simple diagnosis and repair.

Image: Charles01, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons