Trouble codes and identification help needed - 02 XC70

[scot850]

Those who have seen my other posts/threads on the attempt to resurrect this car, will have seen that the car was showing 10 different error messages when scanned, all appear to be engine related.

Having done a lot of work as can be read here:

viewtopic.php?t=105194

During this I cleaned, tested with a multimeter the CVVT solenoid, and also removed, cleaned and tested the cam position sensor due to an error code for cam sensor - low voltage: P0016 or (643A) ECM-643A : Cam Position - exhaust: Signal too low

While I still cannot find any definition that makes any sense on this I still plan to do the oil and filter change as a hail Mary as I cannot find any issues with either sensor. The only other thing I have not checked is that actual timing belt and if the belt was fitted correctly at a recent timing belt change by a Volvo specialist. Maybe I am chasing a ghost and it is cam timing that is wrong?

The 2nd fault code I am fine with as it seems genuine and it is for no signal for the front/up-stream O2 sensor. I plan to swap that when I get the car on the hoist next time possibly for the oil change.

There is a possibly returning one that I have no idea what it is and there seems to be various suggestions what it is for:

(531D) Intermittent Fault ECM-531D : Malfunction indicator lamp (MIL) CEM: Signal missing (P0602)

This seems to point at a checksum difference between the CEM and the ECM. While I understand what this means in technical terms from a computer perspective, it is as we say, "as useful as a chocolate fire guard". That is of zero useful information as to what or where to look for the issue. Has anyone had this code and found a way to fix it?

I was wondering if it is just pointing out there is an issue as shown by the 2 other codes, and is in itself not an issue?

Any guidance appreciated!

Neil.