Need help with P0410 on a 1998 ML320 - PeachParts Mercedes-Benz Forum

DonB · #1 05-09-2012, 06:44 PM

Got the P0410 code (Secondary Air Injection System Malfunction), cleared it, had the local MB specialist look it over...nothing is wrong. Two weeks later it's back. Anyone have suggestions on how to track it down?

mbdoc · #2 05-10-2012, 08:25 AM

Do you hear the electric air injection pump turn on each morning?

ILUVMILS · #3 05-10-2012, 12:20 PM

Quote:

Originally Posted by DonB

.....had the local MB specialist look it over...nothing is wrong......

What did he "look over"? Did he verify the pump actually works? If so, did he check to see if the front O2 sensors are capable of reaching 0 volts?

DonB · #4 05-10-2012, 07:41 PM

mbdoc - It's my wife's car, so I'm not sure. She didn't drive it today, so I:

1. Turn key to on position (idiot-lights all on), engine not started - we hear a distinct buzzing sound. Traced it down with stethoscope, the sound is coming the from rear of the engine, at the end of the air intake duct (see picture #1).

2. Start engine - can't tell if buzzing is still happening (maybe), electric motor at front of engine is running (I think this is the pump - see picture #2).

ILUVMILS - Not sure exactly. Tested the motor and controls; not sure what else. These guys work mostly on German cars, so I think they're pretty sharp. If we need specifics, I can ask.

What's the next step?

ILUVMILS · #5 05-11-2012, 12:09 PM

Quote:

Originally Posted by DonB

.....What's the next step?

Simple. Monitor the voltage of the front O2 sensors with the engine at operating temp. Hold the RPM at around 2,500 until the sensor voltage fluctuates normally. Then, quickly stab the throttle to the floor and lift immediately. On decel, the sensor voltage should drop to 0 volts (or darn close). If the sensors can't reach 0 volts it can cause the air injection system to fail the "self-test". It's actually pretty common on older vehicles. The nice thing about this test is that it only takes a few minutes to do, and doesn't require any parts.

DonB · #6 05-12-2012, 09:34 AM

I'd like to try monitoring the O2 voltages. I located the sensors, but the wires are a bit hard to trace. Is there a good place to clip-onto them, or is this where the MB scanner comes in?

DonB · #7 05-12-2012, 04:36 PM

I can get the O2 sensor reading from my ScanGuage, but haven't been able to decode them yet. Still working on it....

mbdoc · #8 05-11-2012, 08:26 AM

It is normal for the throttle actuator to "buzz" with the KOEO.

Yes, the 2nd picture is the air injection pump.

Now that the pump does run with a cold engine,
you need further diagnosis with a MB scanner that can activate that pump & system.

mbdoc · #9 05-23-2012, 08:25 AM

Does that shop have a scanner capable of activating that system & then seeing what the front O2 sensors are doing?

Or have them watch the O2 sensors in live data & jump the air pump relay & pull vacuum on the diverter valves.

DonB · #10 05-25-2012, 04:43 PM

They say they have a scanner and watched the O2 sensors, just as recommended; but, nothing surfaced.

They didn't do the latest check (watch the O2 sensors in live data & jump the air pump relay & pull vacuum on the diverter valves), but they're convinced that if anything was going to show-up, it would have with tests they ran.

I asked if they thought the dealer might have other tricks to try, but they were pretty skeptical; these guys are pretty seasoned, ex-Mercedes-dealer, mechanics...they're rarely stumped by anything MB or VW.

At this point, we turned-off the CEL and are waiting for something to surface. The car is up for sale, so if we don't identify it beforehand, I'll offer a discount to fix it when it does happen. Don't know what else to do.

ILUVMILS · #11 05-26-2012, 06:54 PM

Hmmmmm...............P0410 isn't really that tough to figure out. I'll assume that your MB guy has done all the diagnostic tests correctly up to this point. What we know is that the pump works, and the O2 sensors are able to reach the test spec under normal conditions. The problem may be that the forced air generated by the pump isn't reaching the exhaust stream. The air passages in the cylinder heads can become clogged, especially on high mileage engines. It's rare, but it does happen.

In post #4 there's a picture of the air injection pump. The two vacuum controlled diverter valves are both clearly seen (one on either side of the pump). With these valves removed, compressed air can be blown directly into the exhaust passages. If this is done while monitoring the voltage of the front O2 sensors, you'll be able to tell if the passages are restricted, or if the air is flowing freely. I've had to do this test a few times over the years and it works well.

One warning though. The diverter valves are very simple to remove (only one bolt each) but you need to be very careful when pulling them out. Don't rock them back-and-forth, even slightly, or they'll probably break. They need to be twisted until they loosen up. It's a small detail but it can be the difference between breaking them or not.

If you find that the passages are clogged you don't have many options. I don't know of any way to un-clog them without removing the heads.

Keep us posted.

DonB · #12 06-04-2012, 07:16 PM

I was considering buying a different scanner so I could run the latest test, but, I just sold the car, so I guess we don't have to pursue it anymore. I want to thank everyone for the help; I would have liked to solved it before handing it over, but....oh-well.

On the brighter side, I just picked up a 2008 ML350, so in the words of the terminator..."I'll be back".