DTC 16795 Secondary Air Injection System - Incorrect Flow Detected

[PeterGAH]

I understand from other threads the Secondary Air Pump can start coming apart and cause this code.

As this works when the engine is cold then seems to shut off does the arrival of a CEL long after starting provide any additional clues.

 

My simple brain tells me if the pump is faulty the CE light should come on when the engine is cold and the pump is running.

 

I am pretty sure it will be more complicated.

 

Any pointers as to which part needs replacing would be most appreciated

 

For the moment I just clear the code and it stays clear for about 200 miles.

 

PeterH

[rwbaldwin]

It could also be the SAI valve (N112).

[pauldazzle]

There are a lot of fault codes that don't trigger the ECU to put the EML on. Most likely the rivets on the SAI housing have failed or you have a split or unsecured SAI pipe.

This pretty much covers it. http://uk-mkivs.net/topic/9315-step-by-step-guide-for-repairing-the-secondary-air-pump-with-pictures/

[pauldazzle]

It could also be the SAI valve (N112).

Yep that would do it too.

[PeterGAH]

Brilliant Thanks.  It seems the point in the journey at which the CEL comes on is not related to the part at fault

I will go through the various checks and see what the rivets are like - The pump rattles like crazy on cold switch on.

Thanks again

[PeterGAH]

I obtained a used Secondary Air pump (New are over £300) and sure enough it was grinning at me around the joint where some of the rivets had given way.

 

So you were spot on guys.

 

I was able to pull out the old rivets with a Chipboard screw and pliers. The most secure ones came out by twisting the point of the kitchen scissors in them. They are made of very thin weak aluminium.

In fact the Aluminium had corroded about 5 mm down the rivet so some of the heads just fell off leaving me to pull the rivet out the other end with the chipboard screw.

 

As I removed the 6 rivets I replaced them with 4mm x 40 Metric machine screws washers and Nyloc nuts. they are all in a kit from homebase at £5.99

 

My local independant Mercedes Audi VW garage swapped them over and I kept the one taken off. It is the same, grinning at me where at least 4 of the rivets have failed. 

 

I have not seen the DT Code now for a large mileage of 380 miles so it was arriving every 60 -80 miles.

 

I think the failed rivets cause an air leak to the inlet system which means the CEL doesn't arrive until the engine is warm.

 

However it is one more problem solved it seems. 

 

Thanks again for all the most useful help.

 

Peter H

[PeterGAH]

I have now travelled over 4000 miles with no CEL after fitting a used Secondary Air Pump that I cleaned and then replaced rivets with nyloc nuts and setscrews.

 

So further thanks to Paul Dazzle for that excellent diagnosi and cure - :sun:

Peter H

[PeterGAH]

EVentually the CEL came back with same code groan

 

After thinking about getting Combi valve changed I used Wynns EGR cleaner squirted into the inlet tract

 

Have not seen CEL for 4000 miles - I think it is sorted now as we go past 209000 miles in this astonishing car.

 

See you at Gaydon

Peter H