I had my pump changed last October and, when the car was in for service in January, the pump wiring was tidy'd up. All has been well since until this latest warm weather. I was travelling, at about 80, up a fairly long hill (not too steep but about 3 miles) the temperature was 21c and bong, reduced engine performance. When the pump problem first manifested it would only bong over 90.

Pulled over and switched off and back on. Immediate bong. Repeat and immediate bong so decided to drive home. Amazingly, no actual reduced engine performance. Ran as normal.

Started the car the following morning, No bong and running fine.

Spoke to my indy and he's going to swap the pump for a new 1 under warranty. It was a BOSCH item. I then got down to some interwebs cruising and found there can be an issue with the fuse for the aux pump, in the boot fuse box.

Does anyone know what the problem is? I found a reference on here and also a bit more info on RR.net but no actual explanation what the fix is. I'm guessing, swap the fuse, which is what I'll do as it's cheap and easy but a bit more info on the actual problem would be really useful.

Thanks 2017 5.0 Autobiography Supercharged
2005 Merc SL350
2005 Disco HSE 2.7 oil burner

I've just had a quick investigation into the boot fusebox to see if there was anything untoward happening.

I found fuse 7 was blown. It's a 15amp fuse and I don't recognise the graphic. I can't tell from the handbook as it's different to the actual car. Mine was a changeover year from 2005 to 2006 and I've got the 2005 handbook and a 2006 car.

Anyway, I pulled a spare 15amp fuse from the glovebox fuse box and popped that into the hole. I then started the engine, switched off and checked the new fuse. Blown again.

I'm not sure if this is the fuse for the aux coolant pump but, if it is, it may point to why I get the reduced performance message, if the pump simply isn't working. It maybe that I've uncovered a new problem

So, can anyone tell me what fuse 7 is for on a 2006 Supercharged. 2017 5.0 Autobiography Supercharged
2005 Merc SL350
2005 Disco HSE 2.7 oil burner

The pump works all the time the ignition is on. You can hear it clearly if you get to the front nearside (near the headlight) with the ignition on.

If you have an IID Tool it is easy to determine whether the pump is working properly. In live values, get it to display the intake air temperature. At motorway speeds the IAT should read around 30c (at 15c ambient). It goes up to mid 40s in traffic. If you see readings in the 60s and 70s your pump is not working. If temps get up to mid 80s you will receive the bong of death and P2601.

Unfortunately the P2601 does not survive ignition off/on so it must be read before the engine is cycled.

The pump is on demand and should not run all the time . 2008 MY Supercharged
Rimini Red / Jet
four zone climate
remote park heater
and no ugly kid windows.
magnus satis quod turpis satis

According to the workshop manual it should run when the ignition switch is in position II

8.
CAUTION: Damage to the charge air cooler coolant
pump will occur if the pump is allowed to cavitate.
• NOTE: With the ignition key turned to position II the
charge air coolant pump will run, to aid coolant bleed. Make
sure the charge air coolant pump is primed prior to running
the pump.

Whether it ever switches off on the move I don't know. I've certainly never noticed mine switch off, and I think one would notice cycling in the IAT temperatures if the pump stopped/started.

I think you have the answer there , it must prime itself on start up . 2008 MY Supercharged
Rimini Red / Jet
four zone climate
remote park heater
and no ugly kid windows.
magnus satis quod turpis satis

A little more investigation has revealed that Fuse 7 (15 amp) is indeed for the Aux Coolant pump. It appears that the vehicle handbook is full of crap and my indy found the correct diagram for the rear fusebox.

What he couldn't tell me was, what, if anything, shares this fuse. In order to find out if the coolant pump/wiring is popping the fuse I will now unplug it, start the engine and then re-check the fuse. If it still blows then that suggests it's not the pump that's blowing the fuse, but something, as yet unidentified, is the culprit.

Does anyone on here know if any other electrickery items share Fuse 7. 2017 5.0 Autobiography Supercharged
2005 Merc SL350
2005 Disco HSE 2.7 oil burner

I was looking at mine yesterday , and can Tell you the plug for the aux pump breaks out of a loom that carries on elsewhere .

Where it goes I can't tell you , but it's fastened coming down the radiator , breaks out to the pump , then carries on fastened to the front chassis rail .

Btw , you can hear/feel the pump start to run in key position 2

Thanks Ian.

The car will not be used till October, at which time it will be off to my indy for the pump wiring to be checked and a new MOT. 2017 5.0 Autobiography Supercharged
2005 Merc SL350
2005 Disco HSE 2.7 oil burner

It's easy enough to check yourself .

You can either use an inspection mirror to look at the wires into the plug , or remove the plug .

Reach in behind the left headlight/air filter box , and under the pump is the connector .
It's a little tight as it sits just above the chassis rail .
There's a metal spring on the plug , facing the wing , that needs pressing in as you pull the plug down .
As you look down into the plug with the spring facing you , the + connection is on the left .
Red/white wire is + .

Just to conclude, it was at my indy yesterday.

They swapped the coolant pump under warranty, had another go at the wiring, got the car up to 90 ish with no bong and the fuse is remaining intact. It appears all is well at last.

It also passed it's MOT with flying colours and they unblocked the rear washer.

The washer was clogged with disgusting gunge like jelly that smelt horrible. The car has been sitting for 6 months whilst we've been in Greece so the washer liquid had deteriorated. Solution will be to empty the tank before we go away next time and flush through with clean water.

Alls well that ends well with the pump and fuse though  2017 5.0 Autobiography Supercharged
2005 Merc SL350
2005 Disco HSE 2.7 oil burner

Did they also check to see if it’s wired correctly ?

Ian, they'd already made the wiring correct when they first fitted the new pump. Still running fine so all is well. 2017 5.0 Autobiography Supercharged
2005 Merc SL350
2005 Disco HSE 2.7 oil burner

That’s great .
Mine needed a new pump when I bought it , but I fitted a new one without checking the wiring .
Then (finally...) checked the wiring a year later and it was backwards

I then had to fit another brand new pump for peace of mind

Luckily , if you buy using the Bosch part number they not as expensive as if you use the rover part number .

A little thread resurrection

I'll post elsewhere about my problem, but just wanted to share what I've found RE: fuse location.

2008MY 4.2 S/C Fatty the fuse that feeds the aux cooling pump is located under the big cover on the left of the engine bay as in the photo, it is a 15A as in the other posts.