Sourcing the correct Zener diode if it is even a Zener diode - markings 1.5KE33CA 0220K
You're in luck!  1.5KE33CA is a part number for a TVS diode.  TVS diodes are not Zeners, but they are the kind of thing which appears on PCBs used in vehicles, especially where wires come onto the PCB. They are used to protect the PCB from transients, and this one is about the right size to protect a 24V system.  Since this specific part is a bidirectional TVS, it should test as open in both directions with a typical handheld meter. The one which tests as 0 in both directions is probably toast, but it would be best to test it off the board to make sure it is that and not something else.
It's a sufficiently common part that most distributors carry them.  My usual go-to has 1700 in stock and sells a bag of five for £3. Other suppliers will also be available.