Frank explains how the ECU is constantly struggling to keep signals within these millions of tiny boxes, in the process generating ‘correction values’. Identify and understand these, he says, and you’ll find out what’s really going wrong: “Accurately diagnosing a fault is like spotting food going off in a fridge. How do you know? You use your nose, you check the sell-by dates… And to prevent it happening again, you control the environment.
“It’s the same with a fault, only we study the electrical signals flowing in and around the suspect component. Often, we find the root of the problem is not the component but the environment – temperature, oxygen levels, carbon deposits – that it’s operating in.”
He quotes the example of a customer at the end of his tether over a long-running problem with his four-year-old Audi A6 2.0 TDI. Frank established that the main dealer who’d been trying to fix the car had been misled by an error code and, running out of options, told the customer it needed a new selective catalytic reduction (SCR) system.
“In fact,” says Frank, “by examining signal strengths and flows, and the wider environment the SCR was operating in, we discovered it was the exhaust gas recirculation cooler that was at fault. Basically, it had an air block.”
Interview over, Frank begins work on his next patient, an Audi R8. With his instruments laid out like a surgeon, an oscilloscope in his hand and a small LED light strapped to his head, he sets to from his favourite chair, illuminated by the glow of a large monitor displaying the car’s electrical pulses.
“He looks like a Cornish tin miner on Mastermind!” quips David.
Even gurus need a thick skin.
Speaking in code
Code readers or scanners aren’t just the preserve of professional workshops – you can buy one from as little as £10. Just plug it into your car’s OBD port (the car’s handbook should tell you where it is) and read off the error code on the display screen. Then consult the code book to find a description of the problem. Users swear by them, claiming they’ve saved fortunes in garage bills.
Vehicle diagnostics expert Frank Massey isn’t convinced.
He says: “The cheapest readers often have a very limited range of codes and their descriptions of the problem can be extremely vague. Remember: a code reflects the symptom but not its cause.”