Secondary Air Check Valve Size and Behavior & GM Pump

Does anyone know if there is a GM part number for this that might be available from the local parts store? Old posts seem to suggest there is but I also saw a post that said it was metric 22mm thread.

Any tips on removal? It looks to me like it would be easy to bend/damage the pipe that it is attached too.

I have the throttle body off to clean it (no problem with the M4-07 screws on the air valve) and thought I might change the air valve if I could get my hands on one.


Regarding behavior (Car warmed up) - when I remove the pipe from the pump and the pump is running I can feel warm air at the end of the pipe. When detached I can hear the the valve which sounds as though it is clicking - open/closed? When attached the pipe becomes hot. The pump pumps air out.

The pipe is not pushing out air - there seems to be marginal suction - very slight. But there’s hot air in the pipe. It seems that hot air is escaping up through the valve when the pump is not running.


  1. Is the valve supposed to be totally closed normally and opens with pressure from the pump pushing air?
  2. I see the pipe is supposed to have an anti-vacuum nipple per Bulletin 05.1-27. I did not look through the pipe but my pipe has nothing on the outside and should have the nipple according to production Vin. Mine is '97. What does this do and is it externally visible or inside the pipe.

I understand the pump only runs at startup so I suspect the hot air is coming through the valve and cooking the pump and back flowing through the air system to the MAF which is a very HOT.


Well - I found the following from TSB 05.1-04.
ISSUE:The CHECK ENGINE MIL illuminates with no loss of power on 1995 MY vehicles within the VIN ranges listed below. Diagnosis with PDU indicates that DTC P0411 is stored in memory.At the end of the secondary air injection cycle, vacuum may become trapped in the hose from the air pump (AIRP) to the secondary air injection check valve (AIRC). The trapped vacuum will not allow the AIRP solenoid operated stop valve (integral with the AIRP) to open during the next air injection cycle. The ECM monitors no drift in the HO2S swings, which triggers the CHECK EN-GINE MIL.A revised air pump hose with a vacuum bleed is fitted to all AJ16 engines in production from VIN 734673 (Sedan [4.0L] Range).

Can someone with a US model take a look at the hose and see if it has a bleed nipple on it? I am not getting a code so I’m not experiencing this problem. Clearly if the valve is leaking there can be no trapped vacuum. But perhaps there will be when I change the valve?

I bought a NOS valve off Ebay for $44. I could not identify the GM version if in fact it exists. I’m suspecting it’s may be an SMP AV56.


I located a new air hose on Ebay in UK. New part # NBC 4798AA on the label which is supposed to have a bleed nipple. I noticed the hose is stamped NBC4742AA - the earlier hose. The seller said it does not a have a nipple.

Is there anyone out there in the US with a 96 or 97 X300 (post VIN 734673) who can check this bleed nipple thing? Earlier models should have been retrofitted as a result of the TSB.
05-1-27A P0411 Insufficient AIR Flow.pdf (57.7 KB)

Nobody have any ideas?

Well…After removing my own I can confirm the existence of a nipple. Hose was fine. Replaced the valve and now the IAT is back to normal.

Incidentally …after repairing a coil wire & replacing a coil connector, plugs, coils (QYL), cleaning the throttle body, replacing the IACV(Stepper motor) the car is now purring flawlessly and the mpg is 25.6 US after a week (mostly highway 95%).

P.S. Back to the XJ40 Cylinder head rebuild.

Well…it is running nicely again. But…P0411, the mysterious secondary air flow code came on today. I know the new old stock valve I put on is good and the hose has the bleed valve. IAT when hot is about 100 deg F. That’s with 90 deg ambient temperature. I need to check the integrity of the connector at the pump next.

Can anyone tell me the part number of a GM replacement pump? I’ve seen it referenced in the archives but no part#. I suspect as the previous valve had been failing for some time it may have caused the pump to start misbehaving. I will check its startup and running behavior as well as the connector in the next few days.