PeachParts Mercedes-Benz Forum - View Single Post - Secondary Air Pump

Syntax26 · #8 06-03-2008, 12:00 AM

Arthur,

Thanks for your quick response. (I was reading some other posts after posting mine - and then I saw you had responded).

You're correct - I was confused about the pump operating or not - but that confusion passed about 2 days ago - and I guess I didn't clarify this.

Originally, not having any experience with this kind of pump - I wasn't 100% sure "what an operating pump looked like". (Not having any history to compare operating versus non-operating). As you know - the pulley is always turning due to the belt - but the triangular face plate at the front of the pump was stationary (on my pump - when the engine was first turned on). I deduced the pump had to have a clutch, and I believed this plate would be seen turning IF the pump was running. But I only figured this out using logic - I didn't know it for a fact.

But once I came up with the idea of putting 12 volts directly to the pump - and saw the change (i.e. saw the triangular plate turn - thus showing me I was right in thinking there had to be a clutch mechanism - and heard the pump operating noise - and then found the suction intake) - then I now had the hands-on personal experience to know the difference between an operating pump and a non-operating pump.

And then I knew 2 things:

1. The pump wasn't running before, and...

2. The pump wasn't defective, i.e. it WOULD run if it got power.

That is what led me to ask you about the relay. And when the local dealership couldn't get identify the part number (meaning I couldn't get and test a replacement relay today), I then came up with the idea of taking the cover off the relay and manually engaging the contact.

As I engage the relay contact - the pump comes on. Clear action - reaction.

So this definitely means the pump, and the wiring harness between the relay and the pump, are ok. It also means 12 volts are getting to the relay (at least one post of the relay, anyway).

Thus the problem would seem to be, by a matter of elimination, that either:

1. The relay is getting the signal from the ICM to close the contact but is not doing so (because the relay is malfunctioning), or

2. The relay is not getting a signal to close the contact.

Now...I'm no expert on relays, but I seem to remember from somewhere that relays are also electro-mechanical. The coil get's enerized, acts like a magnet, and pulls the contact reed to it - thus closing the contact and completing the circuit - and thus sending 12 volts to the pump. Right?

Anyway - I know the next logical step is simply replace the relay. It might not fix the problem, but the relay isn't anywhere near as expensive as a pump - so I'm willing to go this route.

I know it's possible to diagnose more by checking voltage readings in the relay box - in the female sockets. But since I don't have a schematic of this, I'm not sure I'd learn anything.

So I'll wait for a replacement relay. With my luck it won't fix the problem, and then I'll have to bug you for advice again. Hope you don't mind.

So...thanks again for your help.

Jim