5 amp fuse keeps blowing in 2006 Cayenne Turbo. This fuse runs the circuits for two relays - one for the secondary air injection at startup, and the other for the after-run electric water pump. When the secondary air injection pumps can't run, a few CEL related to SAI are set. Has been a real pain to troubleshoot as each of these accessories seemingly only run under very special conditions - either a stone cold engine, or after a hot shutdown. Given that this is my daily vehicle, it isn't convenient to troubleshoot as I am heading out the door to go to work, or in the parking lot - the only time the engine is cold.

Anyway, by trial and error I realized that the fuse doesn't blow as long as the after-run water pump relay is removed. The same is not the case with the secondary air injection relay, so I am guessing there is a problem either with the water pump, the relay, or the wiring. I swapped the water pump relay for another identical one in the fuse box, and the fuse blew sometime after morning startup when I last checked the fuse.

Interestingly, the secondary air injection pump pump ran briefly this afternoon when the engine was up to running temperature and I replaced the blown 5A fuse.

I have still yet to hear the coolant pump run. Of course, to get to the pump the driver front wheel and wheel liner must be removed, which is not a great way to drive the car hard enough to get the pump to turn on after key off.

Is there some clear way to get the water pump to run? I read that it is also used to circulate coolant for the heater core with the engine off, but I tried every combination of setting I could think of to get the relay to energize and blow the fuse during troubleshooting up on jack stands.

It doesn't look like I can easily hotwire the pump in place to check to see if it is OK and there is some hidden wiring or short somewhere.

Ideas and especially experience are greatly appreciated. I'd rather not buy a several hundred dollar pump just to find out it is a short elsewhere.

 

I have some experience with the after-run pump. This is on a '04 Cayenne Turbo w/ 4-zone.

My case did not involve the fuse blowing, but I noticed the after-run pump wasn't activating on hot shutdowns. As far as I can tell there are three ways to test the after-run pump.

1)Get the car hot and turn it off, then listen for the pump.
2)Turn the heat at the HVAC controls all the way up and turn the fan down low (so you can hear the pump), it should activate above 22 degrees C or 75 degrees or so (engine must be warm for this). (unknown: as to whether this only works if the outside temp is cold)

3) Durametric allows you to activate each air-pump individually, and the after-run pump. This is what allowed be to effectively troubleshoot my pump as being failed. Replacement is a bit of a challenge, removing the wheel-well liner and then working in the tight quarters of the fender were the hardest part.

I decided to replace my pump (rather than leave it failed) because it cycles water through the turbos and engine after hot shutdowns. Longevity...

The new pump has a different mounting system too, so get the updated mount when you get the new pump. I didn't have it on hand and used cable ties to hold it. Not ideal, but it works and I trust it.

 

Thanks, I see your logic on point #2 about the settings: fan being low but the temp being high, and the possibility of ambient needing to be comparatively cold. Will play around with that next.

 

So a bit of an update after poking around with the issue. I've been driving around with the driver's wheel well off so that I can feel when the coolant pump is running. I also can unplug the water pump now without taking the wheel off. Drove around all weekend and the fuse never blew... definitely some hot shutdowns with the coolant pump running with no apparent problem. Also a handful of cold starts after an overnight cool-down where the air pumps ran for a minute or so.

I don't have a wiring diagram, but that would be a big help if anyone has one for this circuit. With each of the secondary air pump relays removed, I can jumper the relay socket for each and get these to run reliably. Each one appears to draw about 0.2 amps when running. I purchased this simple diagnostic tool for this purpose:
I can't figure out how to jumper the relay for the water pump. Connecting the two terminals on the relay block that appear to make sense based on the diagram on the relay results in.. nothing at all. I get really weird readings when I try to determine the voltage of these pins relative to battery hot and ground with a multimeter. Hard to explain, but neither appears to probe as hot like the others. I pulled the electrical connector off the pump and tried to measure the resistance - no reading, whereas each of the air pumps gave me a reading at a fraction of an Ohm - seems about right for a brushed motor.

This evening, I was able to blow 3 fuses in a row during a series of warm starts. No air pumps running. Fuse blew faster than I could get out of car after startup to tell if water pump itself was running. I watched the ammeter climb to over 6 amps momentarily one of the times before the fuse of course blew again.

I did notice that the polished pump of passenger side of engine (vacuum?) also seems to pull 0.2 amps on this same circuit when running. I can get it to run by pumping the brakes, especially with the engine off but ignition on.

I spliced in a few extra feet of wire on this fuse buddy and I am now driving around with the water box open and the ammeter readout sitting in the gauge cluster to try to figure out what conditions cause the current surge.

Any other thoughts appreciated. I saw a description for Service Bulletin 320964 and thought it might be related. Anyone know of a source for these?

 

0.2 amps seems very low for the secondary air injection pump. I think my 98 Boxster uses a 40 amp fuse for this component.

 

02A is the current required to drive the control side of each relay, which is what is having issues. The pumps themselves use a different circuit protected by a 40 amp maxi fuse, but I have no issues with that side of the circuit.

 

Well, I found a wiring diagram and determined that the 5A fuse 12 drives the secondary air injection pump relays, the coolant afterflow relay in the waterbox, and the vacuum pump relay.

All of these relays, other than the coolant afterflow, drives each pump directly. The afterflow relay drives... another relay that I need to track down. With this info, I should be able to use my multimeter to figure out if there is a short somewhere in this rat's nest.

 

You can also manually turn on the after run coolant pump by turning off the engine and pressing the REST button on your aircon panel.

 

I tracked the issue down and no issues for about a month, so I think I can claim victory.

There was a multifunction relay up under the driver's side of the dash that was faulty - seems to have had an intermittent internal short. All I had to do was replace it and all the pumps run as they should with no blown fuses.

Went through about a dozen fuses troubleshooting. Found a ammeter that plugs in place of a fuse that was instrumental in solving the issue. Best $12 I ever spent. It let me drive around (and poke around) until I found when and ultimately what was at fault.

http://www.harborfreight.com/30-amp-...ter-67724.html

 

Can you let me know where the relay is you replaced; I look and could not find it. I am having the same issue as you and keep blowing this 5 amp fuse. I bench tested the secondary air pump relays, vacuum relay, after pump relay and check the current draw and getting the same result as you. .2 amp per relay. So I am puzzle that it can draw 6 amps to blow the fuse. I measured like you as well but used a small current meter. Thank you in advance. I will post my findings also. I have 2005 CTT.

 

The relay is under the dash, next to the center console on the driver's side. It faces up, so you won't see it just laying on your back and looking up there. It sits in a grey plastic tray, you need to flip this over to access the relay. If I recall correctly, it was the only relay of that size (tall, narrow) on the tray. To flip it over, there are some click lock tabs you have to release with a screwdriver.

 

Thank you; I will look for it.

Some additional information so just in case somebody gets this in the future: I got a check engine like and the codes were p0418 and p2259; secondary air pump circuit. Then the warning light for brake booster failure came on as well. So I spent time checking the vacuum line for leaks and checked the vacuum pump as well. Well after spending time it was an electrical issue. Once I cleared the errors and use the amp meter for fuse f12 (hitting 6 amps) then no cel and brake booster warning.

 

Okay. I got the relay out. Thank you.

Just to confirm its made by servotronic. Its a really tall one. First time I have seen a relay like this.

Do you know what this relay controls? When I google it seems that it controls the variable power steering...

I am amazed how you found this relay. Did this show on the wiring diagram.

 

I should have taken pictures. It was the same type of relay as several that were in the waterbox. Mine all had "404" written on them. I believe these are all 5-pin multifunction relays. You should be able to swap and test with the same relays in the waterbox.

 

Black, taller than wide. Roughly 2/3 the width of a standard "cube" relay.