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Tech Article

Audi C5 A6 Quattro 4.2 V8 Low Battery Voltage Diagnostic Codes

Last Updated: 09/24/2017
This article discusses the diagnostic codes we saw on our project car, a 2001 Audi A6 Quattro with the 4.2 V8. My intent here is to reassure someone who sees a great many diagnostic error codes that tend to have a common theme of the input voltage being too low.

As to our project car, the seller had told us that the battery was flat, and the engine speed sensor was problematic, but we wanted to learn what else might be wrong. So, once we had the pretty car in our shop, we installed a freshly charged battery, and then I plugged my laptop connector into the car, ran the Ross-Tech software and read the diagnostic codes. Whoa! A great many things were reported to be wrong, all over the car. The engine speed sensor was the only ad-news item I'd expected, and it was indeed there, but so were a great many others. It was a very intimidating list of bad-news items.

However, on closer observation, many of these had a common theme: inadequate input voltage. I concluded that the seller had probablty tried to start the car when the battery voltage was too low, and that this had triggered all of the extra error conditions. We cleared the error codes from memory, and ran the test again. This time, only the engine speed sensor was reported as being problematic. Better!

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