Sudden power loss
This 2005 Audi A4 1.9 TDI was running around quite happily until it approached an incline, when the owner started to feel a distinct lack of oomph. No EML was illuminated and the engine didn’t technically enter ‘limphome’ mode, but it had certainly lost power.
Many motorists are under the misconception that plugging in a scanner will instantly diagnose all problems, but when no codes are in the system (and sometimes even when they are) this is not the case. However, we did have a good idea of the source of the problem with this Audi, and a simple test proved us right. By unplugging the air mass sensor and giving the vehicle a quick spin round the block, we found that power had returned. This is not a definitive test, but very often when the air mass sensor fails it will limit the power, and unplugging it will remove the restriction. Unplugging will also illuminate the EML, which we extinguished after renewing the sensor.
Unplugging the air mass sensor confirmed that it was faulty.