Don't replace the ABS pump so fast!

Folks seem to have the habit of pointing their finger at the most expensive and messy part to replace first as a root cause of a problem with their 993/964. This seems to include the ABS pump.

I have a theory that in the case of what appears to be a non-functioning ABS without any On-Board Diagnostic Codes (OBDC) thrown, a pair of faulty wheel sensors that don't signal may result in what appears to be a pump not functioning. When both are faulty or not in position correctly and are not sending a signal to the controller, perhaps, the controller may think the car is simply not rolling.

Wheel Sensor
in Position

Wheel Sensor Replacement Part

What led me to this theory is I once had a left front wheel sensor OBD fault code that I ignored for a long while as it didn't cause a check engine light (CEL), make the car unsafe to drive and it subsequently simply disappeared.  

Subsequently, the ABS seemed to not kick in so I replaced the relays and checked all the fuses, and from their left things alone as I wasn't prepared to mess with the ABS pump. It got me thinking as to where did the fault go? Then I hit upon the idea that if both sensors were not signaling the ABS controller would think the car is at rest without either wheel turning and so the controller's diagnostics saw no functional problem. I have not gotten around to testing this theory by replacing both of the front wheel sensors but eventually, I will. So, for now, it is just a theory however one that is worth taking into account before contemplating replacing or servicing the very expensive ABS pump.

If one's ABS pump is not working I would test the wheel end sensors to check their position and clean their connections before diving deep into the pump. Also, it seems to me that applying 12 volts to the pump and seeing if it runs may be a good test of the pump. It can also be actuated by some OBD readers however using a reader is also testing any control circuit/relay along with the pump.
Ultimately the 993 pumps can be cleaned or rebuilt if needed.

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