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Old 12-06-2003, 09:32 AM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Actually this is really the worse case code.

In the worse case the air injection passages in the head are plugged and head removal is the answer.

The code is tested real simply with a proper scanner. In activation mode, air injection is selected, the O2 sensor voltage is monitored and close loop is waited for, the air pump is engaged (which also triggers the switch-over valve to pass vacuum to the gatevalve (whatever they call the valve that keeps air from being aspirated into the exhaust when the system isn't workin), and finally the O2 sensor is verified to drop below 80mv.

By dropping to less than 80mv it is proven that a significant amount of air entered the exhaust. This test is done when conditions are correct to evaluate the system. The system actually works before the O2 sensor is heated (and operational in its normal activity).

If on the V8 both sides don't drop, possible causes are the O2 sensors them selves, the gate valve doesn't open (usually a vacuum problem to the valve), and restricted passages and of course the pump.

If the voltage drop is marginal on the O2 sensors one might crack the vacuum line to the brake booster loose. If that air source does drop the voltage easily below 80mv (on later cars with ME the volatge is 40mv) then some restriction or deficiency of the secondary air does exist.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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