2004 E320 drive cycle & secondary air monitor not ready - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 08-01-2018, 12:56 PM

This is all new to me, as I am a Diesel guy. I really like the W211 wagon, but they are only available in gas for US.

I did some searching and reading about this, but found nothing for the 2004 (only older MY's). I don"t know if the procedure is the same for all years. I am trying to smog my car (CA), and am having a hard time. I just read that the drive cycle has to be completed with the A/C off. Could that be the reason this monitor is not complete? It is around 100 degrees here today, but I will try the cycle again (with the A/C off) if that is the thing that is preventing if from completing. The car is already warmed up, and it may take a couple hours to get back down below the desired temp (70*c?). I also read about the forward O2 sensor needing to be perfect. If this is the case, it seems like the least expensive and easiest thing to do. Thanks in advance for any help, Rich

porkface · #2 08-01-2018, 07:29 PM

is the air pump working? replaced alot of them over the years..... if it needs a pump, get a new relay-dealer only-they are updated. good luck, chuck.

97 SL320 · #3 08-01-2018, 08:29 PM

OBD 2 constantly runs monitors under all conditions. The non AC might be for the fast track all monitor test.

The secondary air test on my 97 runs after the engine is warmed up and returns to idle. It runs the air pump then looks for the O2 sensor to read lean ( low voltage for a traditional unit , for a wide band it just looks for a lean condition ) Also, in normal operation the air pump only runs in the first minute after a cold start.

I'd expect the 04 it use the same strategy, listen for the pump to run.

ROLLGUY · #4 08-01-2018, 10:19 PM

Quote:

Originally Posted by 97 SL320

OBD 2 constantly runs monitors under all conditions. The non AC might be for the fast track all monitor test.

The secondary air test on my 97 runs after the engine is warmed up and returns to idle. It runs the air pump then looks for the O2 sensor to read lean ( low voltage for a traditional unit , for a wide band it just looks for a lean condition ) Also, in normal operation the air pump only runs in the first minute after a cold start.

I'd expect the 04 it use the same strategy, listen for the pump to

run.

Quote:

is the air pump working? replaced alot of them over the years..... if it needs a pump, get a new relay-dealer only-they are updated. good luck, chuck.

I checked the pump by powering it up, and yes it is working. I also started the engine cold, and the pump did not come on. I don't have a CEL, so I assume the fuse and wiring are good. Could the relay be bad and not turn the CEL on? Do you know where I can find the relay? I have a parts car (well actually a running usable one), so I can borrow parts for testing.

tjts1 · #5 08-02-2018, 02:14 AM

Try this

ROLLGUY · #6 08-02-2018, 10:30 AM

Quote:

Originally Posted by tjts1

Try this

Been there, done that, thanks. Just this morning I started the car, and the air pump did not go on. I started the sedan, and the pump immediately came on. I pulled relays out one at a time until the motor went off. I plugged it back in to make sure I had the correct one. I took the relay from the sedan, and replaced the one in the wagon. Still no go. I put the relay from the wagon in the sedan, and it seems to work. This all tells me that the relay is fine, but something else is keeping the secondary air pump from activating.

97 SL320 · #7 08-02-2018, 06:17 PM

You need to look for the front O2 voltage to drop when the air pump test is triggered and make sure it is dropping. ( The test runs after engine warm up and engine at idle ) Is there a way to trigger the system through a scan tool?

The 97 era cars have a vacuum solenoid and a vacuum operated valve that allows air to enter the exhaust stream. Make sure this system is working as well.

This might be the engine with air passages in the head that clog up.

For a different engine, I had pitched the possibility of intercepting the O2 signal and reducing it when the air pump is running as a way to fool the computer. You would need a relay wired to be triggered by air pump power. Gold relay contacts are preferred since we are dealing with low voltage / current as silver contacts don't age well in that application and will increase resistance over time.

ROLLGUY · #8 08-02-2018, 11:53 PM

Well, I think I spoke too soon about the relay. I did not get a definitive test with the wagon relay in the sedan. I also jumped to conclusions when the sedan relay did not immediately turn on the motor. I went on an errand, and just for fun I hooked up the scanner when I returned. I noticed that the secondary air monitor was set! It must have actually been a bad relay. I have not had a chance to test the sedan yet. I will try to start it in the morning when it is cold. I suspect the secondary air pump will NOT go on. At any rate, I am happy to be done with this issue. Thanks to all that helped. I learn a lot from the folks on this site.......Rich