So, having stared at the CEL for longer than I care to admit (code P0410, secondary air system), I replaced the air pump motor with the VW model, got a new SAS check valve and a new relay. I thought that would be enough to fix the problem. Wrong. The CEL is on again with the P0410 code.

I tested the motor by running a wire from the battery to the power line for the blower motor. It started immediately. I then tried turning the car on and running a voltage check from the relay connector to the air pump immediately after turning the car on. That had only a few millivolts of power.

Here are a few of my questions: Is the air pump fan supposed to blow after every start, or is it only after a cold start? Does that include a start on a 70 degree day, or is there some kind of thermostat in there somewhere? Am I overlooking some other parts that may be haywire, such as that little connector above the radiator that the SAS check valve vacuum line runs into?

Obviously, I'm a little flummoxed and will be grateful for any suggestions.

 

PAIR (Pulsed Air Injection System) is an assistant to the Catalytic Converter and has a twofold benefit -- help the catalytic Converter reach its normal operating temp quicker, while cleaning the extra-rich exhaust. A Cat without PAIR would warm-up later and deal with richer exhaust (both are bad for it).

PAIR does this by injecting oxygen into the extra-rich exhaust manifold/stream. This oxygen injection cleans the extra-rich exhaust, at the same time increases its temperature, which is good for the Cat.

PAIR operation is controlled by the ECU. Based on pre-determined maps, ECU turns on the PAIR for after about 20 seconds for about 90-100 seconds. ECU uses signals from several sources, starting with both 02 Sensors, Coolant Temp Sensor, MAF, to determine PAIR start. So yes, PAIR may start every time you start the car, if the conditions are met. PAIR operation overlaps a lot with open-loop condition.

Year? Make? Model? Which Motronic (4.3 or 4.4) do you have? This is the setup on Motronic 4.4.

Air Pump has 2 wires -- Green and Black. Black is grounded close-by. The Green wire comes from the Air Pump Relay.

This Normally-Closed Relay has 4 terminals:
1- Green Wire: 12V Feed to the Pump:
2- Pink: 12V feed from the PAIR Fuse (like 50A, Hot at all times)
3- Pink/Black: Signal Wire from the ECU
4- Blue: 12V from the 5A fuse in the Relay Fuse Box in the Engine Compartment (Hot at all times). This is the same 12V feed to both 02 Sensor Heating Elements and PAIR Solenoid.

Question is which terminal did you probe? First, you should check those 2 fuses. If those fuses are good, you should probe the ECU Signal wire. If there is voltage there, but not on the Green wire, the Relay is bad.

Very likely the relay is bad. Volvo relays are known to go kaput. Some people open them and re-solder the connections, some just get them new.

Last thing: ECU Grounds the Pump Solenoid at the same time independently, which turns on the vacuum to operate the PAIR Valve on the Exhaust Manifold.

 

PAIR (Pulsed Air Injection System) is an assistant to the Catalytic Converter and has a twofold benefit -- help the catalytic Converter reach its normal operating temp quicker, while cleaning the extra-rich exhaust. A Cat without PAIR would warm-up later and deal with richer exhaust (both are bad for it).

PAIR does this by injecting oxygen into the extra-rich exhaust manifold/stream. This oxygen injection cleans the extra-rich exhaust, at the same time increases its temperature, which is good for the Cat.

PAIR operation is controlled by the ECU. Based on pre-determined maps, ECU turns on the PAIR for after about 20 seconds for about 90-100 seconds. ECU uses signals from several sources, starting with both 02 Sensors, Coolant Temp Sensor, MAF, to determine PAIR start. So yes, PAIR may start every time you start the car, if the conditions are met. PAIR operation overlaps a lot with open-loop condition.

Year? Make? Model? Which Motronic (4.3 or 4.4) do you have? This is the setup on Motronic 4.4.

Air Pump has 2 wires -- Green and Black. Black is grounded close-by. The Green wire comes from the Air Pump Relay.

This Normally-Open Relay has 4 terminals:
1- Green Wire: 12V Feed to the Pump:
2- Pink: 12V feed from the PAIR Fuse (like 50A, Hot at all times)
3- Pink/Black: Signal Wire from the ECU
4- Blue: 12V from the 5A fuse in the Relay Fuse Box in the Engine Compartment (Hot at all times). This is the same 12V feed to both 02 Sensor Heating Elements and PAIR Solenoid.

Question is which terminal did you probe? First, you should check those 2 fuses. If those fuses are good, you should probe the ECU Signal wire. If there is voltage there, but not on the Green wire, the Relay is bad.

Very likely the relay is bad. Volvo relays are known to go kaput. Some people open them and re-solder the connections, some just get them new.

Last thing: ECU Grounds the Pump Solenoid at the same time independently, which turns on the vacuum to operate the PAIR Valve on the Exhaust Manifold.

 

Henry — Thanks for the detail. It's the 1996 850 NA with, I believe, the 4.4 Motronic. The relay is new from our pals at FCP Groton. I probed the 12 volt feed from the relay to the pump and got nothing. Similarly, when I probed the 12 volt feed to the relay I got nothing. But I am no genius of the voltmeter, so can't rule out that I was doing something stupid.

I'm a little confused here:

2- Pink: 12V feed from the PAIR Fuse (like 50A, Hot at all times)
3- Pink/Black: Signal Wire from the ECU
4- Blue: 12V from the 5A fuse in the Relay Fuse Box in the Engine Compartment (Hot at all times). This is the same 12V feed to both 02 Sensor Heating Elements and PAIR Solenoid.

I'm not seeing any fuses in the engine compartment fuse box for the secondary air system/PAIR. Are these somewhere in-line, or in some other location?

 

Upon digging around a bit further, I found this bit of info related to this p0410 problem:

3. Check for power to the secondary air injection relay. The relay is mounted under the transmission, to the left of the bottom of the radiator, next to the air pump. It has 3 wires, a Blue/Red from the battery, a Blue/Pink from the engine control module and solid Blue going to the air pump motor, mounted next to the relay. This relay is easily damaged by driving through water and may short internally. If it shorts, it can blow the fusible link in the wire coming from B+. If power is OK, activate the relay by grounding the Blue/Pink wire - the pump should run.

I could use some help decoding this line: If it shorts, it can blow the fusible link in the wire coming from B+. What should I be looking for, and where?

Again, thanks in advance for any help.

 

Where did you get that info from?

You you can also go to k-jet.org or http://www.matthewsvolvosite.com/volvo-wiring-diagrams/ to download the wiring diagrams.

 

Your Motronic 4.4 implementation is different from mine. It looks like the PAIR was added to the 850 as an afterthought.

Anyways, yes your statement is correct. There is a fusible link on the 12V that comes from the Battery to the Relay. You need to follow the Blue/Red wire from the Relay.

At one point, there is a Junction, where the Blue/Red wire turns Yellow. This Yellow wire runs to the Positive Post of the Battery.

The Fusible Link is on the Yellow wire, close to the Junction.

ECU starts the Pump, by grounding its Relay, which is what the Blue/Pink wire does. It means, that yes, if you connect the Blue/Pink terminal of the Relay to a known-good Ground, the pump should start, which means the relay is good and Fusible Link is blown.

 

Henry — thanks again for troubling yourself with my problems. The info I cited above, and that you asked about, is here:

1996 Volvo 850 GLT 122K. I just bought it and wont pass inspection - JustAnswer

I've been thinking about this a bit before going out to confront my car again:

"ECU starts the Pump, by grounding its Relay, which is what the Blue/Pink wire does. It means, that yes, if you connect the Blue/Pink terminal of the Relay to a known-good Ground, the pump should start, which means the relay is good and Fusible Link is blown."

If the fusible link is blown, and there is no power to the relay, will grounding the blue/pink terminal matter? I sort of get the spinning nuts part of auto repair, but electric always baffles me.

 

No, run a wire from the battery to the Relay's Blue/Red wire, i.e. sidestep the Fusible Link. Then ground the Blue/pink terminal (not wire that comes to it). Sorry if it wasn't very clear.

This way you test all 3: Relay, ECU signal, and Fusible Link.

 

Again, thanks. Your instructions above are clarifying on this. I really needed the Cliff's Notes version. In the meantime I dug around a bit and found the fusible link. But next, some testing.

 

So, is the fusible link burnt?

 

I did the further testing you recommend and think I established that the fusible link is the problem. I tip my hat to your knowledge. Now I'm a little puzzled by replacing the fusible link, and so just posted this request.

"…I'm no electrical genius, and am hoping for some advice on replacing the fusible link. I went to Autozone and picked up a 14 gauge fusible link. The piece of wire in the carton looks a size bigger than the yellow wire between the link and the battery in my car, so I'm wondering if I should go back and get the next smallest size, the 16 gauge. The link, which is covered in plastic, looks like it just crimps down after you jam the wires in from each side. Correct? I'm assuming the whole thing should be covered with heat shrink wrap."

I hope I haven't worn out my welcome on this. If you have any advice, I'm eager to hear about it. Thanks.

 

What's the rating in the fusible link you removed? In my V90, Air Pump runs at about 25A, and its circuit is protected by a 50A Maxi Fuse.

You can buy a fusible link like this Amazon.com: Beck Arnley 178-3204 Fusible Link - 50 Amp: Automotive, or a 50A Maxi Fuse on a Fuse holder would be perfect.

 

I would run the Pump for a minute or two first to make sure that it works fine, and nothing binds.