S70 T5 1998 Secondary Air Injection Pump doesn't come on

jswoope · Post by **jswoope** » 02 May 2009, 15:40

I recently replaced the secondary air injection pump and injection valve after getting a secondary air injection code. The old pump was not working and the air injection valve was frozen closed. After about a week, the check engine light reappeared with the same code for secondary air. I've determined that the air injection pump is not coming on when the engine is cold at startup. The vacuum switch opens and I get good vacuum on the air injection valve and it is working but I get no voltage signal to the relay for the injection pump. The relay is good, the pump comes on when I bypass the relay contacts, the relay is getting power (positive) with the ignition on, the continuity from the relay coil back to the ECM socket is good, but there does not appear to be an output signal (ground) being set by the ECM. My understanding is the pump relay and motor should pickup at the same time as the vacuum switch to the injection valve and remain on for 1 to 2 minutes during warmup.

Since it appeared the only remaining issue was the ECM itself, I swapped the ECM out with an identical used unit but still have the same problem - the pump does not come on.

Any thoughts on possible solutions to this problem?

Post by **vegasjetskier** » 03 May 2009, 15:07

Possible bad ground wire from the ECM to the relay?

jswoope · Post by **jswoope** » 03 May 2009, 20:30

Thanks for the suggestion. I checked the wiring from the relay back to the ECM with a digital ohm meter and have a good circuit to the pin of the ECM socket.

Post by **vegasjetskier** » 04 May 2009, 08:52

Well if the ground wire is good, the ECM is good, and the relay is good, that only leaves whatever sensor(s) (and their wiring) that tell the ECM that it is time to ground the wire.

Post by **MadeInJapan** » 04 May 2009, 15:45

Are you getting strange temperature fluctuations on your temperature (instrument cluster) gauge? If it's not exactly at 3:00 and holding steady after the car warms up, I would expect that your ECT sensor (engine coolant temp) is going out- when it goes, all sorts of crazy things begin to happen with our cars.

jswoope · Post by **jswoope** » 05 May 2009, 14:24

Temperature guage is steady at 3 o'clock after warmup. This story continues to get stranger by the minute. A Volvo repair shop today scanned the ECM and was able to turn the pump on and off in the test mode. No diagnostic codes were present, no other indications of problems. What ever program logic in the ECM is, for some reason, not telling the pump to start but is telling the injection valve to open. I would have thought they were controlled by the same logic inputs. Very strange. I am sure the check engine light will reappear once the O2 sensor discovers the pump is not coming on after a cold start.

Post by **MadeInJapan** » 05 May 2009, 16:02

Very strange- it's almost as if someone swapped the ECU for one that's not for a car with a secondary air pump, but then this wouldn't make sense because how could a scan tool be used to turn it on? somehow the parameters of air/fuel mixture is off enough to tell the ECU that the air pump does not need to be turned on. That's odd too because mine comes on every time I start the car and sometimes idling at a red light.

jswoope · Post by **jswoope** » 09 May 2009, 15:28

Well, problem solved for now. After the tech used a Multi Tester Pro scanner with Volvo software to turn on the air pump manually in the test mode, it's been working ever since. I installed an LED across the pump relay coil to see when the relay picks up and it comes on always after a cold start and occasionally at a stop light. I also discovered something interesting - it apparently does not come on unless the car is (or has been) in motion. If I wait for it to come on in the garage before moving, it doesn't. That agrees with what the owners manual says about the pump, that it comes on when the engine is cold and the car is in motion.

Thanks for the suggestions.