Mercedes p0412
Been fighting this car for several months. Came in with the usual bad SAI pump. Replaced pump and relay. Had a check valve code come back couple weeks later replaced the valve on the one bank. Had this code for switching valve come a few weeks later,replaced it. Code stays out for several hundred miles and comes back. I can drive car for days and days and SAI system works perfectly but customer will keep it for a week and light comes back. I can not duplicate when I have the car. Any tips or advice would be appreciated
If I recall correctly you should replace the everything at the same time. Pump, right and left valve, and I think there is another valve as well. Otherwise it chases its tail like a ignitor and coil on a old Honda
I've been through a similar frustrating situation with a 06 ML350. System was air tight, always passed the tests on Xentry/DAS. All valves were replaced and working, code kept coming back. Pump good, no vacuum leaks, O2's good etc. Our fix ended up being, by chance, owner needed to replace engine due to unrelated issue. Code never returned with new engine. I believe the passages in the…
Hi Jamie, I don't have the wiring schematics in front of me, but I assume the switching valve connects directly to the DME, so since it's a circuit DTC (as opposed to a performance DTC), it seems like it would be worth checking the electrical connectors and wiring. Check for corrosion at the valve and DME connectors. Then connect your ohmmeter leads to one wire at the the valve connector and…
Here is a flow chart, is your scan tool is a Xentry(?), not sure if aftermarket scanners have the same options/activations/PID's. Hopefully this does give you a baseline to work off of. Note: if the AIS pump is replaced you should replace the relay at the same time, (excessive current from failing pump may compromise the contacts in the relay.) Also, the blue/black check valve is often…
Hi Marty, That's good info. Is the flowchart specifically for P0412 or just overall SAI diagnostics? It seems to be focused on the pump itself rather than the switching valves. Cheers, Don
The flowchart dissects each section of the function chain, so as you follow the chart it will have you check each portion of the components in play. Here is a bit of additional info as to how the system works, but it is likely the next step will be updating the ME control unit…
Thanks for all the replies. I am using the autologic and I scan for it. It does pass the function chain test everytime. I did replace the check valve also. But the p0412 is what I am dealing with now.
Have had multiple car issues where there is poor rainwater drainage left side SAM causing contamination - air pump is high amp draw unit- Causing poor internal contact. monitor relay output to pump at left SAM wire to pump. may be losing current in SAM intermittently.
If customer is the type to use cheap gas, then there is a possibility that the carbon buildup in the passageway can impede the SAI performance. I use B12 chemtool that you find at parts store to at least partially dissolve whatever carbon build up there is. It is a more common issue on the M112 and M113 with their narrower passageways, and B12 chemtool has worked very well to dissolve most of…