Intake pipe switchover valve and cat fault codes

I have 2 issues with my 996 C2 2002. The first is that I cannot activate the Intake pipe switchover valve (I think). I have used a durametric OBD2 reader and activated the valve, but I cannot hear any click from the valve (I can hear a clear click from the valve for the air pump when I try it. The two valves are the same). When I measured with a multimeter in the electric connector for the valve I get 8 volts... What do I test next? The other problem I have is a CEL. I get the below fault codes. P0491 Secondary air-system bank 1 P0492 Secondary air-system bank 2 P0430 Cat. conv. efficiency bank 2 P0420 Cat. conv. efficiency bank 1 P1109 Input variables charge measurement I have after-market 200 cell cats since 6000 miles. I have read that bad cats can trigger these codes, but I have monitored the O2 voltages before and after the cats and according to a Haynes manual I have, the readings indicate that the cats are working properly. What else could it be? Or could the cats be bad even if the O2 readings indicate they are good? Robert

No answers, so I update myself. I have measured the connector to the intake pipe change-over switch and I think the earth connector is fine. As I said before I get 8 volt all the time from the connector when the ignition is on, no matter if I activate the switch or not. I have tried to find the relay for the intake pipe change-over switch but I cannot find it. Usually the wires themselves don't really break so I am thinking it could be the relay that is faulty. Does anybody know where that relay is? Everything has a relay, right? Nothing is plugged right into the Motronic? Robert

There is no relay. Everything is driven directly by the ECU. It's usual to have 12V applied continuously and the ECU switches ground. I do not have the schematics for the Mk2 cars so I cannot confirm. I would not assume that the wires are OK, many times damaged wires have been found.

There is a relay, BUT it supplies a LOT more than just the one change-over valve with 12v. So if you only have 8v at the change-over valve connector, your problem will be "between the change-over valve connector and the take-out splice from the power supply" which is usually not very far up the harness about 6-12 inches.. So if your sure that only the one change-over valve is effected, just follow up the wiring looking for damage (rat gnawing) ..

Yes, I should have been more specific. There are actually three relays: one supplies the ecu/dme and most of the other stuff, one supplies the injectors and coilpacks, and one runs the SAI blower. The changeover valve is supplied from the main ECU relay. Thus, if the ECU is running - and it is if you can use durametric - that relay is working properly. The ECU operates the valves/injectors/colipacks by supplying ground - there is no individual relay for these items. So please follow Skip's instructions and check for battery voltage on the other connectors and inspect for wiring damage. The power to the changeover valve is shared with the camshaft adjusters, there's a welded wire connection in the engine harness. So you might check voltage at the camshaft adjuster connectors to verify power there and limit the scope of your troubleshooting. Also please be sure that you're measuring voltage from the terminal in the plug to an actual ground. Measuring voltage between the two pins of the connector won't get the job done.

Yes, Aaron is correct, use an "actual ground" when testing with a DVOM. The change-over valve connector doesn't have an "actual ground", the DME/ECU provides an " intermittent ground" through the processor to activate the change-over valve when necessary/optimal for control of the valve.

Quotes source post: 17538781

If I activate the camshaft adjuster with my durametric and it clicks, then I don't have to measure the cables, or? I mean, if the camshaft adjuster works it must have power. Am I correct?

Quotes source post: 17538514

Ok, thank you, good to know. Sure, a wire could be damaged, but the wires from the change-over switch goes into a thick cable harness after just a few inches. It is not easy to find any damages in that harness. I am thinking I'll try and measure the resistance from the two big round connectors to the right in the engine bay to the connector for the change-over switch. Zero resistance = the cable is ok? Robert

You can certainly ohm out the wires. The white on the changeover valve goes to X59/1 pin 10. The red/blue on the changeover valve goes to X59/1 pin 8. My notes say that X59/1 is the top round plug with the black circle inside. X59/2 is the bottom round plug with the gray circle inside. Yes, 0 Ohms = continuity. Anything less than 1-2 ohms will be OK.

Ok, so the 12 v power to the change-over valve is shared with some other functions. Where are all the cables with the shared power connected together? At the ECU relay in the rear shelf in the back seat? Or is it in the engine harness? Robert

They're welded together in the engine harness.

Now I have measured the two cables from the change-over valve to the X59/1 connector on the right hand side of the engine bay. I measured 1.5-2 ohms for both cables, so that should be ok. I also measured the power supply to the change-over valve with the ignition on, and that showed 12 volts. This means that everything seems fine in the engine buy. I guess it must be something in the ECU. Robert

I concur with your analysis. Before condemning the ECU I would check the wire between the X59/1 pin 10 and the ECU connector III (three, the 52 pin plug) pin 4.