Thanks Bob,

I should add to the above... If the probe's housing is damaged they tend to read artificially high for a given insertion depth; obviously not the case with your engine.

If the probe fails such that the circuit is broken, the GDT will misinterpret it and display 979C. This can be due to a fault in the probe, a broken wire, or a connector that's poorly connected to the lead. I know this isn't the case here, but I've been asked about it a few times over the years so it's probably good info to add for others reading this thread.

Kelly