Hello, I'm looking for the fuel pump control module on my 62 plate tdi. It's not on top of the tank nor tucked under the edge of the carpet. The pump harness goes into the sill void and emerges by the bonnet release and I'm pretty sure there's nothing in between. Logic tells me it's going to be somewhere under the dash, but just not seeing anything remotely like it. Any suggestions would be greatly appreciated. 

Do you actually know that such an animal exists?

 

The ECU would command the pump, there would be a relay involved probably amongst the others by the battery, its just possible that the switching could be done in the body control module with the ECU communicating via Canbus.

Thanks for replying, JR. I have no hard physical evidence, but researching my fuel issues, I keep coming across references to the pump control module. there are photos of said unit sitting on top of the tank access panel and plugged into the top of the pump. Could it be that this is only for petrol engines? Anyway, if it's not there I can't fix it! But I'm not having much luck with the main issue which is the fuel pump isn't running. I fitted a new one and cleaned the tank out (lot of crap in there!), but the new pump doesn't run. I've swapped the relay with an adjacent one, but no joy. Took the relay out and put a jumper across the contacts and the pump runs. But should it run constantly? Is there a control unit, somewhere, that regulates the delivery? If it's the ECU, then it doesn't seem to be doing the job! Sorry, that's a lot of questions, but I'm floundering with this one.

That sounds more like the fuel level sensor incorporating the roll over check valve.

 

I'm sure I had that out on my MK2 but cant recall where the pump connection was, it definitely has one in the tank which is initiated for a short burst when the ignition is switched on, mind you mine was a PD engine, yours will be a CR engine.

You need to explain what your "fuel issues" are/were and why you replaced the pump, is the engine running now? Was it before?

 

The pump will definitely not run constantly unless the engine is running, it may prime when you open the drivers door or turn the ignition on but then stop, this is a mandatory safety feature.

 

To help you we need more detail than "I am looking for the pump control module", like why are you looking for it?

 

If it exists.

1 hour ago, JDW133 said:

I'm floundering with this one

Send your VIN in a private message and I'll see if a control module is fitted to your car. Have doubts.

That will also give me exact age of car in order to look at best wiring info to try to help.

 

The OP sent me his VIN, which confirmed the non-existence of a fuel pump control module on his car.

 

Form what he's already tested with respect to the relay (J17 below) I think the next things that need verifying are the feed and control line to the relay coil, as depicted below. Engine bay fuse 15 will be a good one to check, as it supplies the power to the coil (likely only when ignition is on or engine running), and the connection ringed which shows the control connection from engine ECU (Continuity test of that would be ideal).

The various wires ending in rectangles are all fairly irrelevant to the investigation I think, though the one with 79 in it goes to the glow plug control unit, which will also be non-operational if the fuse is busted. G6 is the fuel pump motor.

Thanks for the details Pete. I have checked F15 and it's good (5amp). Have also tested the relay and connections and 

established the following:

 

1. The fuel pump relay (above the obd port) has permanent live on pin 3

2. With the ignition on, pin 1 is live 

3. The relay will activate if pin 2 is connected to a separate earth, with ignition on. 

4. Connection to the pump is good and the pump runs if the relay is activated. 

Good work.

Next step is to test the wire between engine ECU and relay holder for continuity (does it read 12V at relay socket pin 2, or something else, with relay not in place, and ignition on?)

 

 

Edited 6 July, 20232 yr by Breezy_Pete

Pin 2 has 3.43v

Pin 1 has 11.8v

Not as conclusive as I'd hoped.

 

Not sure what else to suggest than a continuity test from ECU connector pin 46 to relay socket pin 2.

Okay thanks for that Pete. I'll have a look at this tomorrow. I should explain, this car belongs to the charity I work for (we provide mobile changing places for disabled people) and we use it for towing our caravan to events. 

So, two and a half weeks later. I had a look at the ecu, saw it was encased in a metal cage with sheared off screws and decided not to go there! I'm thinking that the ecu will power up the tank pump in response to a signal from a pressure sensor on the low pressure side of the fuel system. If I'm right, can someone please point me in the general direction of this sensor? Also, with most diesel cars, the pump is triggered when you unlock the door. Is that the case with this particular model? If so, why is it not doing just that? Does this point to the same pressure sensor? I've checked the output on pins 1 and 2 with the door open, shut locked, etc. Nothing changes. 

On 06/07/2023 at 17:27, Breezy_Pete said:

Good work.

Next step is to test the wire between engine ECU and relay holder for continuity (does it read 12V at relay socket pin 2, or something else, with relay not in place, and ignition on?)

 

 

@Breezy_PeteWith the relay removed there should be no voltage on pin 2 as the relay coil has been removed, the 3.48v is probably a floating open collector voltage if thats the right term, I plumbing my memory banks.

Others with similar engined Octys may confirm/deny the fuel pump activation. My limited experience and viewing of circuits suggests it's a petrol engine thing, and works with driver's door opening, not unlocking.

 

@J.R. I was expecting either 0V, possibly indicating a busted wire, or it being pulled up to 12V within the ECU when dormant. The inbetween voltage makes me unsure and suggest the continuity test.

 

On 06/07/2023 at 17:56, Breezy_Pete said:

Not as conclusive as I'd hoped.

 

Not sure what else to suggest than a continuity test from ECU connector pin 46 to relay socket pin 2.

 

Agreed.

 

Also its time for a VCDS scan before theorising about pressure sensors, the fault is likely to be revealed and the operator can also force the operation of the fuel pump which will prove the integrity of the circuit, the relay (already tested) and the switching transistor of the ECU.

Just now, Breezy_Pete said:

I was expecting either 0V, possibly indicating a busted wire, or it being pulled up to 12V within the ECU when dormant. The inbetween voltage makes me unsure and suggest the continuity test.

 

Yes I agree now things are returning to my brain, I remember using pull up or pull down resistors on my circuit designs, I think an open collector was something to be avoided for interference reasons.

Thanks for your input guys. I'll borrow some diagnostics next week and see what comes up.