Secondary air injection system fault
 

1997 Mercedes E320 emissions check from Autozone diagnosis probable causes:

1. Circuit relay defective or fuse open
2. Check connector and wiring
3. Air pump defective or hoses blocked

Suggestions or pictures of where any of these problems can be located?

ACR

not saying this is your problem, but more often than not when that system activates when cold, meaning the pump runs and all plumbing is in order, what usually is an oxygen sensor rather than the air injection system itself. the way it tests for air pump activation per obdII regulations is it measures how far the voltage for the oxygen sensor before the cat drops when air is introduced into the exhaust gasses via the air pump, if it doesn't drop fast or far enough it will set a code for airpump system. so technically your complete air injection system could be fine, but a bad o2 sensor before the cat can cause this code to appear. to determine exactly, you will need a diagnostic tool that acan monitor the o2 sensor voltage while the air pump is activated, at work we use the factory tool that can electronically activate the air pump and monitor the sensor voltage, and what i do if the voltage doesn't drop correctly with activations i create a large vacuum leak by disconnecting the brake booster and watching the o2 sensor voltage, it really should drop well below 40mv within 5-15 seconds, if it does then likely the air pump sysem is not working correctly, if it does not drop correctly the o2 sensor is usually to blame. hope this helps, good luck

A carboned up/dirty o2 will also bring on an AIR code b/c it is not capable of getting to the low volt/ lean read Carson is talking about..sometimes this required 02 sensitivity will come back after a good hard run under load..[ which cleans/clears up the sensor]

Thanks for the advice. Since I do not have a diagnostic tool to monitor the o2 sensor voltage is there any other way to check the sensor. This part costs $142 new and if I can get away with not buying it that would obviously be better.

acr

You want to verify AIR system is coming on before doing a 02 changeout..the 02 is just the feedback testing device that monitors the AIR system.. if the pump is not running when it should, the 02 sensors has nothing to report.................the first question to look at would be is the pump even coming ON ???
Your problem could be as simple as a bad fuse or broken vac line.
As Carl stated , the 02 sesnor will fool the guy doing the diagnostics when ALL ELSE in the AIR system seems to be funtioning properly, BUT you still get a code ..so, you have to verify the system first before going right to the 02 sensor...if the system/pump is not even coming On , the 02 sensor is the last place to look.

Where is the physical location of the secondary air pump on the 1997 E320 (straight six)?
tia