berkeleyEE
07-02-2008, 05:21 AM
In my 1996 328is the SAP relay is located in the front power distribution box in relay position 1 (1 out of the 15 possible).
I was tracking down the dreaded F5/F6 fault codes and found my Pierburg air pump was dead (internally corroded with a trickle of water falling out of the electrical connector at the base!) and the check valve on the exhaust manifold was carbon coated and frozen open.
Following the excellent instructions by GP Burdell (formerly of Georgia Tech) I replaced those parts but not the rubber hoses, they were flexible and uncracked.
Before removing the failed pump, I was sure I measured +12VDC at the pump's plug. But after installing the new parts, I was trying to check the electricals by cycling the electrical power ON/OFF. And I wasn't seeing 12V at either the SAP plug nor at the electrical relay that controls the vacuum to the check valve.
So I attempted to trace the wiring: nearly impossible in the amount of armored wiring in a BMW. And I wanted to locate and test the SAP power relay, which is not clearly identified in my Bentleys.
Here's how to identify the SAP relay. According to the schematics in Bentley the pump motor is switched by a power relay between battery +12V when energized and vehicle ground when not energized. Take your ohmmeter and measure the resistance between the two sockets in the plug on the harness (NOT the pins in the receptacle on the pump, there you'll just measure the DC resistance of the wire in the motor).
If the wiring is continuous and the relay in the proper normally-closed state then the ohmmeter should read near 0 Ohms (a short). It probably won't be exactly zero if the meter is uncalibrated, and also there is real (non-zero) resistance in the copper wire and in the contacts of the relay.
Now go the fuse box and start pulling relays one by one: pull one out, check your meter, put the relay back in. If you know which of your relays are just the 5-prong ones, then you need only pull those. When you pull the SAP relay the circuit is now completely open and the meter will read a very high (infinite or over-load) resistance. In my vehicle I started with relay number 1 and immediately found the SAP relay. Which was _not_ salmon colored, it was just another generic purple 5-prong relay.
The relay checked out OK, but I still did not get +12V to the SAP when firing up the engine. My theory is that the DME is programmed with a bit too much smarts: it counts the number of recent engine starts and figures if the engine has been recently started then there's no need to run the SAP.
So I let the car sit overnight. When I started up, the SAP blew for about a minute as it should.
423183
-Jerry
I was tracking down the dreaded F5/F6 fault codes and found my Pierburg air pump was dead (internally corroded with a trickle of water falling out of the electrical connector at the base!) and the check valve on the exhaust manifold was carbon coated and frozen open.
Following the excellent instructions by GP Burdell (formerly of Georgia Tech) I replaced those parts but not the rubber hoses, they were flexible and uncracked.
Before removing the failed pump, I was sure I measured +12VDC at the pump's plug. But after installing the new parts, I was trying to check the electricals by cycling the electrical power ON/OFF. And I wasn't seeing 12V at either the SAP plug nor at the electrical relay that controls the vacuum to the check valve.
So I attempted to trace the wiring: nearly impossible in the amount of armored wiring in a BMW. And I wanted to locate and test the SAP power relay, which is not clearly identified in my Bentleys.
Here's how to identify the SAP relay. According to the schematics in Bentley the pump motor is switched by a power relay between battery +12V when energized and vehicle ground when not energized. Take your ohmmeter and measure the resistance between the two sockets in the plug on the harness (NOT the pins in the receptacle on the pump, there you'll just measure the DC resistance of the wire in the motor).
If the wiring is continuous and the relay in the proper normally-closed state then the ohmmeter should read near 0 Ohms (a short). It probably won't be exactly zero if the meter is uncalibrated, and also there is real (non-zero) resistance in the copper wire and in the contacts of the relay.
Now go the fuse box and start pulling relays one by one: pull one out, check your meter, put the relay back in. If you know which of your relays are just the 5-prong ones, then you need only pull those. When you pull the SAP relay the circuit is now completely open and the meter will read a very high (infinite or over-load) resistance. In my vehicle I started with relay number 1 and immediately found the SAP relay. Which was _not_ salmon colored, it was just another generic purple 5-prong relay.
The relay checked out OK, but I still did not get +12V to the SAP when firing up the engine. My theory is that the DME is programmed with a bit too much smarts: it counts the number of recent engine starts and figures if the engine has been recently started then there's no need to run the SAP.
So I let the car sit overnight. When I started up, the SAP blew for about a minute as it should.
423183
-Jerry