Audi A6 Avant 3.0 TDI AdBlue Fault No Start in 500 Miles.

DTC’s Present: P20E800 – Reductant Pressure too Low.

This vehicle was recently presented to us with an AdBlue warning on the dash: ‘No start in 500 miles’.

The owner reported that he had already topped up the AdBlue (Diesel Exhaust Fluid) but the warning hadn’t disappeared.

It is important to note that AdBlue warnings on the dash can be triggered by 2 means:

  • Low AdBlue fluid level
  • Fault within AdBlue system

Armed with this information, we first verified the level of Adblue which was found to be correct.

The quality of AdBlue was then tested. AdBlue consists of 2 components: Distilled water and urea. Contrary to popular belief, the urea content is synthetically manufactured and is not pigs wee! The Urea content was found to be spot on at 32.5%.

Happy that we had sufficient quantity and quality of AdBlue, we then scanned the vehicle for any Diagnostic Trouble Codes – DTC’s.

We found: P20E800 – Reductant Pressure too Low

(Reductant being AdBlue)

A healthy AdBlue system operates at 5 bar, so the next step was to see what pressure our system was operating at. We tested at the injector and found no pressure present.

The next question that needed an answer to was: ‘Do we have a pressure generation issue, or are we losing pressure somewhere?’

Further tests were carried out and it was found that the AdBlue pump (Reducing Agent Pump V437) was not working. All wiring to the pump was tested and verified. It would be a pointless and fruitless exercise to replace the pump if we were just missing a power, for example. The pump is a 3 phase pump and good knowledge and skills are required to test accurately.

The pump was replaced and all post replacement procedures and adaptations were followed.

An extensive road test was carried out and the ‘AdBlue No Start’ warning extinguished almost immediately.