DIY: Troubleshooting S.A.S. and How to Replace the Famous Fuse # 107!
- I have emission codes P1421 and P1423 (S.A.S. codes saying not enough air is injected into the exhaust during cold start), which is very common for car this age 10y/100K miles.
- In order to understand the S.A.S. system, you need to read the attached pdf on S.A.S.:
---> In brief, when engine is cold, the Air Pump injects additional air into the exhaust to reduce pollutants.
---> The Air Pump is designed for high output but short run, so it injects air for anywhere between 2.5 seconds and 105 seconds or so, depending on engine temp.
- These are PNs for 1998 528i, listed only for reference, later years are slightly different. This is taken from www.realoem.com:
* Electrical Valve; PN 11747537612 (about $45)
* Air Valve: PN 11727540467 (about $110)
* Air Valve Gasket; PN 11727505259 (about $4)
* Pierburg Air Pump; PN 11721427911 (about $250)
* Air Pump Relay (K6304): schema is 85-86 and 30-87a-87, PN 12631742690 (about $8)
* Fuse #107: 50A Special Fuse: BMW PN 61138365901 ($4.00); Napa PN 782-1144 ($4.00). The BMW Fuse is covered in black and you cannot check it with your naked eyes (need Voltmeter or Ohmmeter to check). The Napa Fuse is see-through: within a glance you can see the fuse is good or not. I prefer the Napa Fuse. See pic:
- To be sure the Air Pump is bad, remove it and apply 12V to the 2 pins, if it does not run, either the bearing is seized or the motor is gone. You have 2 options:
1. New Pierburg Air Pump is about $250.
2. Rebuild the Air Pump using a standard bearing SKF 626 (ID = 6mm; OD = 19mm ; W = 6mm). Complete Air Pump Rebuild Info is here:
http://www.bimmerfest.com/forums/showthread.php?t=402816
This is the sequence of S.A.S. system when you start the car cold:
- ECU sends signal to the Electrical Valve (this Valve sits under the Intake Manifold), which in turn opens a small channel to allow vacuum from the Intake Manifold to be applied to the Air Valve (which sits on the Exhaust Manifold)
- At the same time, signal is sent to the Relay to close the 85-86 "primary" circuit, which in turn closes the 30-87 "secondary circuit". In general, the "secondary circuit" in most Bosch relay circuits controls the high current flow.
- In the case of the S.A.S. Air Pump, the 30-87 circuit is controlled by the Fuse # 107, which itself is under the passenger's seat, thanks to the BMW engineers who designed this car with beer and bratwurst!!! In any other car, replacing this fuse is not hard because it is usually located under the hood. In the E39, Fuse 107 is a bit tricky to get too, but not too bad.
SOME DIAGNOSTIC PROCEDURES:
- Check the small Vacuum line leading to Air Valve, it is usually cracked with time/heat.
- To check Electrical Valve, during cold start, Disconnect (D/C) the small vacuum hose and feel for vacuum, there should be some vacuum from the small hose b/c the Electrical Valve opens the port to allow vacuum from the Intake to the small hose. Now re-connect the small hose.
- Air Valve and Gasket testing: Disconnect (D/C) the large hose to Air Valve, start engine during cold, after a few seconds there should be vacuum at the Air Valve (feel with your palm of your hand), if not either the Air Valve itself or the Electrical Valve is bad.
- Air Pump Testing: At the same time as above, the Air Pump is activated, so you should feel air blowing out of the large hose that you just disconnected above, if not, then the culprits are:
a. The Fuse #107 is blown. When this happens, usually something else is bad (like Bad Air Valve allowing water from exhaust to enter the Air Pump, destroying the bearing is blown ---> the Air Pump is dead. If the Air Pump is shorted electrically, the new fuse will be blown again. So if the fuse is blown, investigate it further. In my case the Air Pump was seized.
b. S.A.S. relay is bad (rare).
- Before getting to Fuse #107 under the passenger seat, check the S.A.S. Relay and its connector first!!! The Main Fuse Box is under the passenger side Cabin Filter. Remove the Passenger Cabin Filter Housing.
- Using Allen keys, open the Plastic Cover and you will see the setup below with all the main relays and some fuses here. To check the S.A.S. Relay, remove it & check for continuity between 30 and 87a, it should be 0 Ohm. Now apply 12V to 85 and 86, 30 and 87 (not 87a) is now connected.
- Now check the Relay Connector, take note of the relay pinout, then copy it to a piece of paper because when reading relay upside down, it is very very easy to get all the connector terminals mixed up! By copying the terminals numbers (basically mirror image of the relay) to a piece of paper, you eliminate error! Over the years, I have learned this the hard way, so trust me with this copying to a piece of paper. There should be 12V to #30 terminal all the time. See pic:
PROCEDURE TO REPLACE FUSE #107 UNDER PASSENGER SEAT:
Now that you have determined that there is no power to terminal #30 in the Relay Connector itself, time to check and replace the 50A Special Fuse.
1. The Trim piece: using flat screw driver pry it up, it is held by 3 White clips.
2. The Seat is held by four (4) Torx #50 bolts, remove them but no need to take the seat out of the car.
3. The Vertical Trim piece: undo the bottom part only to allow the carpet to be folded back.
4. Note how the carpet fits (the front carpet piece slides under the rear piece).
5. Fold the carpet back and place a brick on it to hold it there to free your hand. You will see a Styrofoam insulation piece. In order to remove the Styrofoam in its entirety, you have to remove the plastic tunnel (HVAC Tunnel), which is more work! I bypassed this step: I leave the plastic tunnel alone but break the styrofoam at where it meets the plastic tunnel b/c it is a only a piece of insulation, nothing fancy about it.
- Use a short piece of wood to prop the seat up about 12".
6. Now you see the Electrical Distribution Center, remove the white plastic covers to expose the Red (+) connections. Ground (Brown Cables) is just to the Left of this distribution box.
7. Fuse Block has a total of 8 fuses. Fuse #107 is on the far Left. See picture:
8. To test the Fuse, use a Voltmeter (not Ohmmeter for now).
9. Note the Large Red Feed Cable side, it feeds power to the electrical block where it branches out. So probing on that side must read 12V or so. Now probe the other side of the fuse, it should read 12V as well, if it reads 0 volts, the fuse is bad.
10. To replace the 50A Fuse, it is held by 8-mm nuts and square washer. Use a small hook to hook it out. Remove the fuse and confirm that it is bad with an Ohmmeter: when a fuse is bad it reads infinity Ohms (open circuit).
* CAUTION: this circuit is always "hot" with 12V, even with key out of ignition! If you are not comfortable working with "hot" wire, then disconnect the red cable from the trunk battery. I did this whole thing with the battery connected, just pay attention not to touch any ground while removing the 8-mm and 10-mm nuts.
11. The medium-sized red cable feeding separate electrical items in the car is held by a single 10-mm nut.
12. NOTE the torque for these nuts, basically tight and snug a bit:
* 8-mm nut: 8 Nm
* 10-mm nut: 15 Nm
13. Now you need to address the Air Pump. Either buy a new Air Pump or rebuild it, otherwise this fuse will blow again! Info for Air Pump is mentioned above.
That is all boys and girls, not too difficult if you know what you are doing!
- I have emission codes P1421 and P1423 (S.A.S. codes saying not enough air is injected into the exhaust during cold start), which is very common for car this age 10y/100K miles.
- In order to understand the S.A.S. system, you need to read the attached pdf on S.A.S.:
---> In brief, when engine is cold, the Air Pump injects additional air into the exhaust to reduce pollutants.
---> The Air Pump is designed for high output but short run, so it injects air for anywhere between 2.5 seconds and 105 seconds or so, depending on engine temp.
- These are PNs for 1998 528i, listed only for reference, later years are slightly different. This is taken from www.realoem.com:
* Electrical Valve; PN 11747537612 (about $45)
* Air Valve: PN 11727540467 (about $110)
* Air Valve Gasket; PN 11727505259 (about $4)
* Pierburg Air Pump; PN 11721427911 (about $250)
* Air Pump Relay (K6304): schema is 85-86 and 30-87a-87, PN 12631742690 (about $8)
* Fuse #107: 50A Special Fuse: BMW PN 61138365901 ($4.00); Napa PN 782-1144 ($4.00). The BMW Fuse is covered in black and you cannot check it with your naked eyes (need Voltmeter or Ohmmeter to check). The Napa Fuse is see-through: within a glance you can see the fuse is good or not. I prefer the Napa Fuse. See pic:
- To be sure the Air Pump is bad, remove it and apply 12V to the 2 pins, if it does not run, either the bearing is seized or the motor is gone. You have 2 options:
1. New Pierburg Air Pump is about $250.
2. Rebuild the Air Pump using a standard bearing SKF 626 (ID = 6mm; OD = 19mm ; W = 6mm). Complete Air Pump Rebuild Info is here:
http://www.bimmerfest.com/forums/showthread.php?t=402816
This is the sequence of S.A.S. system when you start the car cold:
- ECU sends signal to the Electrical Valve (this Valve sits under the Intake Manifold), which in turn opens a small channel to allow vacuum from the Intake Manifold to be applied to the Air Valve (which sits on the Exhaust Manifold)
- At the same time, signal is sent to the Relay to close the 85-86 "primary" circuit, which in turn closes the 30-87 "secondary circuit". In general, the "secondary circuit" in most Bosch relay circuits controls the high current flow.
- In the case of the S.A.S. Air Pump, the 30-87 circuit is controlled by the Fuse # 107, which itself is under the passenger's seat, thanks to the BMW engineers who designed this car with beer and bratwurst!!! In any other car, replacing this fuse is not hard because it is usually located under the hood. In the E39, Fuse 107 is a bit tricky to get too, but not too bad.
SOME DIAGNOSTIC PROCEDURES:
- Check the small Vacuum line leading to Air Valve, it is usually cracked with time/heat.
- To check Electrical Valve, during cold start, Disconnect (D/C) the small vacuum hose and feel for vacuum, there should be some vacuum from the small hose b/c the Electrical Valve opens the port to allow vacuum from the Intake to the small hose. Now re-connect the small hose.
- Air Valve and Gasket testing: Disconnect (D/C) the large hose to Air Valve, start engine during cold, after a few seconds there should be vacuum at the Air Valve (feel with your palm of your hand), if not either the Air Valve itself or the Electrical Valve is bad.
- Air Pump Testing: At the same time as above, the Air Pump is activated, so you should feel air blowing out of the large hose that you just disconnected above, if not, then the culprits are:
a. The Fuse #107 is blown. When this happens, usually something else is bad (like Bad Air Valve allowing water from exhaust to enter the Air Pump, destroying the bearing is blown ---> the Air Pump is dead. If the Air Pump is shorted electrically, the new fuse will be blown again. So if the fuse is blown, investigate it further. In my case the Air Pump was seized.
b. S.A.S. relay is bad (rare).
- Before getting to Fuse #107 under the passenger seat, check the S.A.S. Relay and its connector first!!! The Main Fuse Box is under the passenger side Cabin Filter. Remove the Passenger Cabin Filter Housing.
- Using Allen keys, open the Plastic Cover and you will see the setup below with all the main relays and some fuses here. To check the S.A.S. Relay, remove it & check for continuity between 30 and 87a, it should be 0 Ohm. Now apply 12V to 85 and 86, 30 and 87 (not 87a) is now connected.
- Now check the Relay Connector, take note of the relay pinout, then copy it to a piece of paper because when reading relay upside down, it is very very easy to get all the connector terminals mixed up! By copying the terminals numbers (basically mirror image of the relay) to a piece of paper, you eliminate error! Over the years, I have learned this the hard way, so trust me with this copying to a piece of paper. There should be 12V to #30 terminal all the time. See pic:
PROCEDURE TO REPLACE FUSE #107 UNDER PASSENGER SEAT:
Now that you have determined that there is no power to terminal #30 in the Relay Connector itself, time to check and replace the 50A Special Fuse.
1. The Trim piece: using flat screw driver pry it up, it is held by 3 White clips.
2. The Seat is held by four (4) Torx #50 bolts, remove them but no need to take the seat out of the car.
3. The Vertical Trim piece: undo the bottom part only to allow the carpet to be folded back.
4. Note how the carpet fits (the front carpet piece slides under the rear piece).
5. Fold the carpet back and place a brick on it to hold it there to free your hand. You will see a Styrofoam insulation piece. In order to remove the Styrofoam in its entirety, you have to remove the plastic tunnel (HVAC Tunnel), which is more work! I bypassed this step: I leave the plastic tunnel alone but break the styrofoam at where it meets the plastic tunnel b/c it is a only a piece of insulation, nothing fancy about it.
- Use a short piece of wood to prop the seat up about 12".
6. Now you see the Electrical Distribution Center, remove the white plastic covers to expose the Red (+) connections. Ground (Brown Cables) is just to the Left of this distribution box.
7. Fuse Block has a total of 8 fuses. Fuse #107 is on the far Left. See picture:
8. To test the Fuse, use a Voltmeter (not Ohmmeter for now).
9. Note the Large Red Feed Cable side, it feeds power to the electrical block where it branches out. So probing on that side must read 12V or so. Now probe the other side of the fuse, it should read 12V as well, if it reads 0 volts, the fuse is bad.
10. To replace the 50A Fuse, it is held by 8-mm nuts and square washer. Use a small hook to hook it out. Remove the fuse and confirm that it is bad with an Ohmmeter: when a fuse is bad it reads infinity Ohms (open circuit).
* CAUTION: this circuit is always "hot" with 12V, even with key out of ignition! If you are not comfortable working with "hot" wire, then disconnect the red cable from the trunk battery. I did this whole thing with the battery connected, just pay attention not to touch any ground while removing the 8-mm and 10-mm nuts.
11. The medium-sized red cable feeding separate electrical items in the car is held by a single 10-mm nut.
12. NOTE the torque for these nuts, basically tight and snug a bit:
* 8-mm nut: 8 Nm
* 10-mm nut: 15 Nm
13. Now you need to address the Air Pump. Either buy a new Air Pump or rebuild it, otherwise this fuse will blow again! Info for Air Pump is mentioned above.
That is all boys and girls, not too difficult if you know what you are doing!