Information on diagnostics

Opel/Vauxhall EGR valve

error messages with new parts

Why does the malfunction indicator lamp light up when a new EGR valve has been installed? What is the procedure when the diagnostic trouble code P0400 appears? Is the control range in the control unit too small? Find out how you can solve this problem in this article.

Suitable for: Opel/Vauxhall

Product: EGR valve


Pierburg no.

Replacement for

Ref. No.*

Agila 1.0i/1.2i; 12V/16V, Astra G/H/Mk IV/Mk V 1.2i/1.4i; 12V/16V,
Corsa C 1.0i/1.2i/1.4i; 12V/16V, Meriva 1.4i 16V, Tigra B 1.4i 16V



8 51 593


  • Signal voltage outside tolerance
  • New part with error message
  • Malfunction indicator lamp lights up
  • Diagnostic trouble code P0400

Every EGR valves has a characteristic curve in the form of a hysteresis. The hysteresis has tolerances based on manufacturing technology, i.e. each EGR valve has a slightly different hysteresis. For this reason, there is a control range in the control unit into which the hysteresis must fall. An error message is displayed if any results fall outside of the control range. In the example shown in Fig. 1 this would refer to all of the red areas of the characteristic curve that fall outside the control range (for example the green area).


In the case of the aforementioned EGR valve it is possible that the control range in the control unit has been set too small. An update of the engine control unit software can be used to extend the control range, thereby solving the problem.


In simple terms, a hysteresis is a characteristic curve that takes a "different route back from the one it took to get there” (see Fig. 2).

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