I have a new bit of diagnostic kit, FIXD, it is giving me code P1621 that related to “memory loss” Any ideas? The car is running fine !

 

See page 121 - 132 for your 1996 , The Jaguar code in their Jaguar list does not exist or accounted for on their side

The code sounds familiar as others have had it , there is some discussion on it in other threads

There is a thing called heartbeat monitor ( a fault flag indication on aircraft windshear systems ) we had in a different field that refers to as a computational check that the system is changing to verify it is still calculating ( in this case maybe fuel trim calculations in how much fuel to deliver ? )

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I have had a look at those codes and as you say , it is not listed. I will remain vigilant!