W203 annoying secondary air pump fault

[Dizwen]

Hello everyone, the car is giving me a weird repeating fault that I hope someone can help me get to the bottom of...

The car engine management light (MIL) came on and a quick trip to the dealer diagnosed a "secondary air pump fault". They wanted to charge me £500 to replace the pump, but a quick look under the bonnet showed me this thing was just behind the passenger head light, easy to get at and bloody huge!

Easy to DIY this one. I got a air pump (£125, with a two year warranty) and got the relay from the dealers (£7). Just under an hour of my time, pump swapped, relay fitted and the MIL disappeared after a reset (I've got cheap diagnostic plug tool that will do that) happy days...or so I thought...

The MIL popped back on after I'd been driving the car for an hour. Quick check with the plug in and it says "secondary air pump fault". I reset the fault and no issues for over a week until it came back on again after I'd been in the car for half an hour. wtf? The MIL has now come back on 4 times and resets with no issues.

I understand (correct me if I'm wrong...) the air pump comes on when you first start the car to pre-heat the exhaust (it's basically a hair dryer for the CATS to get the emissions down) and turns off after a minute or so. The pump can burn out if the relay sticks causing the pump to run constantly (which is why you change pump and relay as a pair) but why would it cause a MIL after the car has been driven and is up to temperature?

Before I start pointing the finger at faulty pumps or relays and swapping parts under warranty, have I missed something?

It all seems pretty straight forward to me (pump+relay=job done) Should I have done something else for this type of job?

Car:
W 203 C32 AMG

 

[markjay]

Have a read here:

P0410 code SOLVED ! ! ! ! ! - MBWorld.org Forums

 

[pillow]

"secondary air pump fault" is awfully vague. There are a number of elements to the secondary air system that can go wrong and unless you get hooked up to DAS you won't know otherwise.

Presumably now you have a new pump it is working fine (I would assume that the old one is fine too) however the problem could like in the valves or vacuum lines.

As to why it would happen when up to temperature. The secondary air system is part of the I/M readiness tests. The secondary air injection test runs as part of this and usually happens 7 minutes after a cold start once the car returns to idle for more than 6 seconds. I.e. if you cold start and drive around for 7 minutes, pull up and idle for 6 seconds then it attempts the readiness test.

 

[whitenemesis]

I had a "secondary air pump fault" appear on my S203, the usual "we must replace XYZ" from the dealership.
A very good independent quickly diagnosed a loose wire in the loom connector to the top/front of the engine. Pins re-seated and all fine..

 

[C32Hero]

"secondary air pump fault" is awfully vague. There are a number of elements to the secondary air system that can go wrong and unless you get hooked up to DAS you won't know otherwise.

Presumably now you have a new pump it is working fine (I would assume that the old one is fine too) however the problem could like in the valves or vacuum lines.

As to why it would happen when up to temperature. The secondary air system is part of the I/M readiness tests. The secondary air injection test runs as part of this and usually happens 7 minutes after a cold start once the car returns to idle for more than 6 seconds. I.e. if you cold start and drive around for 7 minutes, pull up and idle for 6 seconds then it attempts the readiness test.

Hi. I am pretty new to the forum and to Mercs - I currently have a 2001 C32 (yes I know I jumped right in for my first Merc) and although I'm happy with it, I have now got a decent list of small and medium jobs to do on it. one of these, is looking at the noisey secondary air pump. it functions exactly as Pillow mentioned but does so with a decent racket. if these are reasonable to swap put along with the relay, can anyone share the part numbers please?

ill never turn down a little help on how to change the pump either! much appreciated all.

 

[C32Hero]

I should say, there are no other symptoms. just one hell of a whirring noise

 

[Dizwen]

Have a read here:

P0410 code SOLVED ! ! ! ! ! - MBWorld.org Forums

Well, Christmas is out of the way and I finally got some time to go through the tread and try some of the solutions.

I believe that the fault was caused by scale build up in the vacuum tubes (circled). I removed the tubes and scraped out a large chunk of white scale with a small pin from both tubes.



reset the MIL and all has been good ever since.

Thanks for the help!

regards,

Paul

 

[Dizwen]

Hi. I am pretty new to the forum and to Mercs - I currently have a 2001 C32 (yes I know I jumped right in for my first Merc) and although I'm happy with it, I have now got a decent list of small and medium jobs to do on it. one of these, is looking at the noisey secondary air pump. it functions exactly as Pillow mentioned but does so with a decent racket. if these are reasonable to swap put along with the relay, can anyone share the part numbers please?

ill never turn down a little help on how to change the pump either! much appreciated all.

I got my pump here:

Secondary Air Pump For MERCEDES W203 CL203 S202 W463 W221 A0001405785 | eBay

I know it's flea bay but it does have a two year warranty so I was happy to buy it.

As for the relay, I went to a dealer as I didn't want to take any chances.

The pump itself is easy to replace (green circle)
:

remove the engine cover
remove the air inlet hose to the air filters
unplug one push on hose from the side of the pump
unplug one electrical plug from the top of the pump
unscrew 3 retaining bolts from a bracket holding the pump in place and lift out

Put the new pump in place and plug everything back on - easy! (and the dealers wanted £500...)

Hope that helps

 

[pillow]

White scale?

Odd, that tube should hold vacuum only. I wonder what that scale could be.

 

[Dizwen]

White scale?

Odd, that tube should hold vacuum only. I wonder what that scale could be.

Best guess some kind of build up from condensation in the system? It's all I can think of tbh, but I might be totally wrong...