Where did Flo Go?
Some where in there is a dump valve. After checking the VSV for proper operation and confirming the Air Pump actually pumps air, it’s time to dig into the engine to test the valves and clear the Air passages if possible. Removing a few choice components on the Porsche 911 makes access to the divert-er or “Dump” valve and check valve possible. Porsche uses a vacuum reservoir to help vacuum operated function during low engine vacuum conditions. It is mounted on a fixture which bolts over the air passages we are looking for. Ahhhh! there it is. The very dangerous and highly elusive Dump valve. I think I’ll make it mad.
The larger threaded hole is where the check valve attaches to the fixture and the more silver colored smaller threaded hole is for the air line that feeds the right cylinder head. The check valve will be replaced even though it still passes air. More importantly shop air will be forced through the air passages in an attempt to open them so the Air can reach the exhaust side of the cylinder heads.
Air line to the right side cylinder head
So we’ll blast out the passage ways, reassemble and test the Secondary Air injection. Manually starting the pump we got an acceptable voltage change in the O2 sensors. After two drive cycles the On Board Diagnostics, checked off the Secondary Air Injection as functioning properly. It’s now OK to turn the car back to the customer with the cravate that we can not know how clean the passageways are. They are not likely to improve but are passing enough air at this time to satisfy EPA standards as programmed into DME and monitored by OBD II.
How does the Engine management know?
A plugged Secondary Air Injection Port on a Mercedes Benz M112 V-6
So the air pump is not accomplishing it’s task of heating up the three way catalyst. How does DME (Digital Motor Electronics) know any way? Programmed into the computer is a self test of the air pump. Each time the car is started DME at some point in the drive cycle will turn the air pump on to see if it’s working. How it sees is interesting. Part of the fuel management system are oxygen sensors or on newer cars AF (air/fuel) sensors or broad band oxygen sensors report back to DME. By sensing the amount of oxygen in the exhaust gases these sensors allow DME to make adjustments to the air fuel mixture going into the engine for the most efficient performance under all conditions.
The O2 sensors also tell DME if the air from the air pump is reaching the catalyst. If the secondary air injection system is working properly DME should see a drop in voltage in a conventional O2 sensor. On the newer A/F sensors the technician will need to access fuel trim data to see if the fuel system is trying to adjust when the air pump is artificially triggered. So the air pump pumps air but there are some mechanical controls in the way of the air actually getting to the exhaust side of the equation. There is a vacuum switchover valve (VSV) and a vacuum operated “Dump Valve” that when vacuum is applied by way of the VSV allows air to enter the exhaust through a check valve which keeps exhaust gasses from returning through the “Dump Valve” damaging it and the pump.
So the long and short of it is, the DME turns on the Air pump, the sensors sense no change indicating A Secondary Air Injection malfunction or low flow and DME turns on the Check Engine Light. Now what? Dig in.
One of them there tools that fixes Check Engine Lights
So we’ve decided to take the bitter pill. We have been dealt a P0411 secondary air injection malfunction. To understand what that means we’ll have to understand what the secondary air injection is and what it is meant to do when operating correctly.
Generic Scan Tool
We’re mostly familiar with the catalytic converter that has necessitated the use of unleaded gas since around 1975. 3-way catalytic converters break down hazardous carbon monoxide to harmless carbon dioxide. They also break down toxic hydrocarbons into carbon dioxide and water while reducing nitrogen oxides to regular nitrogen and oxygen. For the Cat to do it’s job it has to be hot which can take a while. In order to meet strict emissions standards an air pump has been added to heat the Cat up sooner and reduce harmful emissions quicker. Pump air into the exhaust and it gets hot more quickly. When the Cat reaches 400 to 600 degrees Fahrenheit it begins to clean up the exhaust.
To let you know if the emissions system is working properly a number of self diagnostic regimens have been programmed into the engine management systems. One is a self test of the air injection or secondary air pump. If that self test fails your check engine light illuminates and a P0411 diagnostic trouble code is stored in your engine management processor. In this case the processor is called DME. Not a fun as MMI but DME serves it’s purpose.