2005 Envoy 4.2 L

[Fox1]

This is the third time I have posted with the same problem: MIL with a code P0410 secondary AIR injection system malfunction. It started last spring, with your help I determined it was the pump. Replaced the pump and everything was fine until about 6 weeks ago same code. Pump was OK and I determined it was the relay and replaced. Went for about 3 weeks same code. Checked the check valve did not function and replaced. Almost immediately same code. Pump works when I jumper the relay. Relay works when I apply 12 volts. Cleaned the contacts where the relay plugs in. The check valve clicks when I apply 12 volts so I am assuming those three components are functioning properly. I checked the switching voltage to the relay zero. The two fuses and relay for the AIR sys are OK. Any suggestions? Thanks in advance.

[thopkins]

first, the relay receives ground signal from the pcm to command on. so your test light will need to be connected to b+ to see if command signal is present. it is not gonna run all the time. it will self test briefly when the engine is first started. it may not command on with a fault code present so you will not have switch signal at the relay in your case. every time i have seen any type of failure with air injection especially on the envoy or trailblazer it has always been due to water in the pump or in the system.. remove the line that connects to the valve, the one at the air box and at the pump under the vehicle and blow out the lines with shop air. if there is no water in the system and you are sure all components are working otherwise replace the b1 or upstream 02 sensor. the pcm moniters the pre cat 02 sensor when the air system is activated and it should drop below 130 millivolts when on. if the 02 is lazy or sluggish it will set the p0410. good luck

[Fox1]

Thanks thopkins,

Considering the weather today it will be a few days before I get back to it. I'll let you know how I come out.

[LightningBG]

I had the same problem when you posted the first time.

when the vehicle was cold (over 4 hours without running), I took off the hose going from the pump to the check valve (technically solenoid valve). Start the vehicle.

At this time if the pump is working and the signal is being sent, that hose will be shooting a lot of air out.

If the solenoid is working, it will be open, and there will be an unmistakable howling noise.

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When I did mine, there was air blasting, but no noise. I took the solenoid off and cleaned it thoroughly, and even had to yank on it with a locking pliers to get the plunger to move at all. Then I tested it with a vexilar battery and made sure it was popping up and down. Reinstalled, reset the check engine light and all has been fine since.

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I know this doesn't really answer your question, but you need to start narrowing down where the problem is. (solenoid/pump&relay/signal)

[Fox1]

It turned out to be a lazy o2 sensor. It checked out fine except a little slow when I would remove it from the heat. Replaced it and the MIL has not returned.

Thanks all, for your help.