Originally Posted by
Michaeldemi
Are you sure? I just want to make sure so I don't replace another part and it not be it... I replaced the combi valve and $145 late I'm still with the problem. These cars are a pain in the rear. Replacing all the air flow pieces (they all dried up and cracked after a while) was a pain in the end. Took one off and the other breaks and so it went...
I may confirm that it isn't a broken tube from the SAI to the air filter before I buy an SAI....
Here's an additional question -
I can go about 300 freeway miles without the CEL coming on. But if I go through rough loads it turns on within 15-30 miles. What may explain that? The P0411 code is the same, but it will come on at different intervals - depending on the condition of the road I'm driving on.
The P0411 DTC has no functional association with the roughness of the road when the DTC is set. The relevance of the stored DTC frequency is associated with the number of cold starts not the mileage driven. Since the specific DTC fault condition should only be monitored when the SAI pump is operating, The only exception to this limitation, is if the vibrations driving on a rough road provoke shorts in the wiring somewhere, incorrectly activating the SAI pump. This is speculation only, I can't really think of any plausible malfunction theory that can explain how the DTC is setting on rough roads, since the functional aspects of the SAI have no road roughness association, except as a wiring or ECU glitch.
The DTC "Incorrect Airflow" description, means the SAI output airflow is not effecting the exhaust gas oxygen concentration consistent with the OBDII SAI monitor exhaust oxygen specification for when the SAI is active.
Bosch Motronic ME7 OBD System Strategy :
".05.00.00 SECONDARY AIR SYSTEM MONITORING
.05.01.00 Via lambda deviation
.05.01.01 General Description
After cold start condition (e.g. 5 .. 40°C) the Air system blows for a certain
time air into the exhaust manifold. The exhaust gases will be enriched with
oxygen and post combustion of HC and CO occurs. By this exothermic
reaction the exhaust system will be heated and the time to reach the lightoff
temperature of the catalyst will be accelerated.
Principal main components of Air System: (example 4 cyl. Engine)
ECM;
Air pump relay
Air valve (solenoid valve)
Air valve (vacuum controlled)
AIR pump;
O2 Sensor;
The monitor of the secondary air system distinguish between two functions:
a) Passive monitoring function will be carried out during normal secondary air injection
While engine is cold started and
b) Active monitoring function will be activated later during the driving cycle, if the passive
Monitoring function has not a pass result
At idle state or under part load engine condition, the secondary air pump is switched on and the valve
opens either by pressure of the pump or vacuum operated by switching to “open”, causing an
increase in the air fuel ratio. The Oxygen Sensor control function (closed loop) enriches the mixture
consisting of exhaust gas of the engine and secondary air until the Lambda integrator signal will meet
a predetermined value (functional or flow check).
Check Conditions
Passive Monitoring Function
To start the passive monitoring function, following conditions have to be
satisfied:
Oxygen sensor readiness
No engine restart (thermal energy introduced)
A certain time after engine start
Engine has been cold started
No output stage error from secondary air pump relay
Active Monitoring Function
To start the active monitoring function several conditions have to be
satisfied:
No result or no “pass” result from passive monitoring function available.
Engine running at idle
Closed loop condition of the Lambda-control
Monitoring function not done before (for pump protection)
No output stage error from secondary air pump relay
Furthermore, if the diagnosis has already been started and one of the
conditions has not been satisfied continuously, the process will be
interrupted.
The following conditions have to be fulfilled additionally:
All adaptations of the air/fuel system are inhibited
The Lambda controller has been stabilized (waiting for several transients of
the oxygen sensor signal)
The actual Lambda controller value has been stored
In case of an interrupt of diagnosis, the monitor can several time started
again (different for each test group; see overview) during the same driving
cycle if the monitor conditions are met."
Besides the incorrect air flow from the pump to the combi valve, if the combi valve operating vacuum pressure hose connection is disconnected or the N112 solenoid valve is faulty, or combi valve control vacuum pressure hose is cracked or split, will prevent the combi valve from opening when the ECU activates the SAI. If the pump is running under unstable flow conditions, against a blocked discharge flow path with the combi valve not opening properly, can result in noisy pump operation with compressed air in the pump housing flowing into the pump then stopping and reversing flow out the inlet port, repeating at high frequency.
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