Is my reasoning here a plausible explanation for the issues described below?
The CEL on my friend's 2003 Mazda6 lit up yesterday, along with a flashing HOLD light. We hooked it up to a code scanner and found the following codes stored:
P0767 - Shift solenoid 'D' Stuck On P0841 - Transmission Fluid Pressure Sensor/Switch "A" Circuit Range/Performance P0733 - Gear 3 Ratio Incorrect
The car was not shifting beyond a certain gear while the CEL was on. We used the scanner to clear the codes and CEL light and then went on a brief test drive in which the issue did not recur and the gear shifts were routine.
We also found the transmission fluid was very clean, but the level was very high. I've requested the car to be taken to a mechanic where some of the excess can be drained out.
The friend says this is the first time this issue occurred. The unusual thing he did was drive the car immediately after starting it up; he normally leaves it to warm up slightly before driving.
Here's what I think happened
My suspicion is the P0841 is the reason behind the CEL, which was triggered by a combination of a request for Gear 3, the ATF level being too high and the fluid relatively cold.
If there is too much ATF in the transmission, I suspect that the pressure sensor may "malfunction" because it is reading an unexpectedly high pressure.
I also believe that the P0767 is just indicating that the transmission couldn't shift gears when needed, while P0733 is just indicating which gear it had trouble shifting into (Gear 3).
On the contrary
It could be that there really is a stuck solenoid inside the transmission, but the condition of the fluid on the dipstick leads me to think otherwise.
Of course, it could be that a previous owner attempted to fix this issue by refreshing the ATF (as opposed to routine preventative maintenance), but that is something that can only be verified by cracking the transmission open.