TACH-cluster replacement-resetting ODO?

[CTScott]

Originally Posted by cali yaris

That is correct. I don't even have an ECU in the car any more (standalone management for my project) - the gauge cluster holds the mileage, and the speedometer and fuel gauge still work.

The cluster can operate independently of the ECM (or in your case in lack of the ECM). The ECM also stores the 3 mileage values in its FLASH ROM. When the cluster is swapped the two will disagree. The question is what happens at that point - Does the ECM simply update its values from the new cluster, does it stop updating them until something is done to rectify the mismatch, or can it force the cluster to take its values?

The people who swapped the clusters hot, saw the clusters' mileage remain. The one person who was told to disconnect the battery by the junk yard dudes saw the cluster mileage change to his correct mileage on power-up.

The service manual makes no reference to this or to the procedure for updating the cluster's mileage. It does mention using the Techstream tool to update the ECM's mileage after it is replaced, but nothing about the cluster.

At this point, I'd like to see a second person disconnect the battery before performing the swap to see what the result is.