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| The SAI pump with its vacuum-controlled outlet valve attached by a hose to the lower left. |
Here is how I would proceed to test the SAI system:
- If you are using Durametric to diagnose the SAI system make sure you are using the latest software from their site. If not, first uninstall what you have and reinstall the latest version, clear, and rerun the code. Durametric had a known issue related to oxygen sensor-derived codes on earlier software revisions and also with their old-style cable and software.
- Replace the SAI check Valve, discussed on this page:
https://993servicerepair.blogspot.com/2020/02/emission-control-systems-horror-of.html
- Detach the hose to the new check valve and with the engine dead cold have a friend start the car when you are behind it. If the air pump is working and the vacuum-controlled valve attached to it is opening you will hear what sounds like a jet engine sound for just a few seconds coming from the hose and strong air movement which is the pump running. It should be reasonably loud.
This test can only be done once at an initial cold start or again much later from a dead cold engine.
if your OBDC reader features actuations one can turn the pump on manually as well although I am not sure it will also actuate the control solenoid valve for the vacuum controlled valve attached to the pump outlet. For this reason the sound from the hose may be blocked by the valve. If the valve doesn't open with the pumps actuation it will be unclear if the valve or its solonoid is not working or the actuation function on your OBD reader just turns on the pump and doesn't open the valve.
- If no sound is heard check the vacuum tube connection to the solenoid connected valve. If the valve seems to actuate but the pump seems to not run
- Check the SAI fuse and relay located in the fusebox on the left-hand side of the engine compartment.
- If the fuse is good, clean its spades and put it back in, and test or replace the relay.
- If the fuse is blown then the wires to the pump have probably failed and shorted out a known issue on the 993/964, how to fix them is discussed on this page:
- If the pump & valve check out as ok then buy the two oxygen sensors for that side of the car, bank 1-3 (left side) or 4-6 (right side) based on the OBD Code listed and replace them. Many cars have older sensors that can contribute to an erroneous SAI fault code and the attendant Check Engine Light (CEL). Evaluation of the signal from the Oxygen Sensors to validate their proper operation can be problematic for the shade tree mechanic however if purchased in the Bosch branded box they are not too expensive and are easy to replace. Here is a page that describes how to replace them in your driveway:
- With new oxygen sensors, a new check valve, and verification that the pump and its vacuum control valve is working the next step is to clear the OBD code and see if it returns.
If the code returns you probably will need to have the ports cleaned as described on this page:
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