Mercedes secondary air

Roddy Technician Ontario Posted   Latest   Edited  
Delayed
Emissions
P0412 — AIR System Switching Valve "A" Circuit

Hi guys and girls. I'm pulling my hair out on this.

Originally the car came in with 3 related p0412 codes. Found a shorted and seized air pump and blown 40amp fuse. Replaced both and the light keeps coming back telling me that the switching vale has a short to power, yet it works just fine with bi directional controls from scanner. Decided it must be intermittent and put a new switching valve/solenoid in and a few days later I get a code pointing to the bank 1 diaphragm valve. Found it was stuck so I cleaned it out. The customer jus called to say that the light came back on again. There was a pending code for p0412 switching valve short to power after cleaning the bank 1 valve but after 5 cold starts it hadn't triggered the light and it hadn't beed seen by the OBD2 side of the computer either. Hoped it would go away….but sadly it stil want to haunt me befor Hallowee. Any suggestions? Aside from a partia leakin diaphrag on bank 2, I'm stumped. 

-1
Missing Vehicle
Marty Technician
California
Marty
 

VIN #… year and model? What kind of scan tool are you using? The air pump relay should have been replaced too…also see attached bulletin, ( 1.4) indicates update M.E control unit.

+2
Ð Awarded
Thanks
Roddy Technician
Ontario
Roddy
 

I didn't replace the relay as of yet. I thought I had put that it was a 2011 mercedes c300 in the post. I guess it didn't show up. Are they bad for the relay acting up?

0
Ð Awarded
Roddy Technician
Ontario
Roddy
 

Also I'm using the snapon modus and the snapon verus….at least I think it's the verus. Both seem to have the same functionality either way.

0
Ð Awarded
Marty Technician
California
Marty
 

Do they have an actuation option? Can you watch live data to see what the O2 sensors are doing during Air pump operation? The relay is an important replacement item especially when the air pump failure occurs…the excessive current draw often will burn the contacts in the relay. The codes you are coming up with appear different than the factory codes, so just trying to find out if the system…

+1
Ð Awarded
Thanks
Roddy Technician
Ontario
Roddy
 

I seemed to have full functionality of the pump and the vacuum solenoid while using the scanner to turn them on and off. Initially the pump was seized up and there was water and rust in it. Bank 1 diaphragm valve was stuck with carbon witch I cleaned and seemingly fixed. Unfortunately I don't have the car as it's currently 2 cities away. Just trying to gather some info to formulate a plan of…

0
Ð Awarded
Marvin Owner/Technician
Texas
Marvin
 

What is the year and model?? VIN??

0
Ð Awarded
Roddy Technician
Ontario
Roddy
 

2011 mercedes c300. I don't have the vin on me.

0
Ð Awarded
Jamie Mobile Technician
British Columbia
Jamie
 

Hi Roddy, Can you measure the VTBRN wire at the ME control unit pin 53? The relay would not be an issue for the P0412 as your code just pertains to the switching valve being open circuit. This means the ME is seeing something less than battery voltage when the valve is NOT commanded on. If the voltage is good at the back of the connector, check the pin itself for proper fitment.

+2
Ð Awarded
Thanks
Roddy Technician
Ontario
Roddy
 

Don't have the car yet. One of those (phone rang and “hey guess what” situations) I've been able to activate both pump and solenoid on command multiple times during testing over the past week. Would find it odd to have it be a loose pin or wire and never having it fail in the service bay. I'm definitely no expert on mercedes though so when the car comes I'll check pin53. Now, what's confusing me…

0
Ð Awarded
Jamie Mobile Technician
British Columbia
Jamie
 

I’m not sure if you’re looking at OE info or a generic obd2 code? The official definition is: Y32 (Air pump switchover valve) : Open circuit (P0412) Does your code set right away if you clear it? I always like to look at the signal with a scope when dealing with an electrical fault. Then you can actually see what is on the circuit and see what the computer is seeing or should be seeing. Just…

0
Ð Awarded
Roddy Technician
Ontario
Roddy
 

Yes, that would be the code that shows up on the scan tool.. except it said short to positive instead of open circuit 🤔. Hmmm, I'm starting to wonder now if there's a translation issue for this code in our snapon scanner…or if somehow I've managed to read the code wrong on multiple occasions over the course of 2 weeks? Either way I have a guy going out there this weekend who will scan the code…

0
Ð Awarded
Roddy Technician
Ontario
Roddy Delay
 

The customer scanned the vehicle over the weekend, it didn't turn out to be the p0412 code. Instead it was the code for the bank 1 valve stuck open. This is the valve that I had cleaned and got unstuck. Currently the follow up on this diagnosis is in a state of delay because I don't think the customer is ready to drop money into replacing those valve's and still have the possibility of the check…

0
Delay Ð Awarded