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· Registered
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Discussion Starter · #1 · (Edited)
I'm getting 2 faults that come back after I clear them:
Pin 8, codes 9 and 35.
Code 9 = O2S 1 (before TWC) (G3/2) sensor voltage
Code 35 = AIR pump switchover valve (Y32) and/or 23 28.0
electromagnetic AIR pump clutch (Y33)

Any idea what the next step is? Do I just replace the O2 sensor or might it just need cleaning?
I will replace the switch over valve.
Is the air pump clutch part #104-140-14-85-81. Is it easy to test?

1993 w124 320CE pre facelift 124.052

Thanks for your advice

· Registered
6,622 Posts
If it were me I would find a reasonably priced O2 sensor and replace the one in the car. They only are supposed to last 60k miles. As for the switchover valve, before replacing it you might first check the integrity of the vacuum hoses connected to it. If they are okay, check that vacuum is available to it from the manifold. If either of these are in trouble, changing the valve will buy you almost nothing.

· Premium Member
2014 G550, 2000 SL500, 1995 E320 Cabriolet, 1980 TR8
1,979 Posts
^ I agree - replace the O2 sensor as see what happens with code 35.

As I understand it, for cars without the Diagnostic Module, the ECU measures the current drawn by the air pump clutch and the switch over valve. If this value is not correct code 35 appears on pin 8. For cars with the DM, the ECU actually performs a functional check for air being injected into the exhaust stream (I think it uses the O2 sensor for this test). If the test fails, it sets code 4 on pin 3.

If both codes don't clear with the new O2 sensor, check the electrical connections at the front of the engine and the condition of the wiring. You can also easily measure the resistance of the clutch/switch over valve in the connector on the front of the engine. It should be around 3 - 4 ohms with a good DVM.
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