Article [13] ST1300 - Fuel Pump Circuit - Fault Diagnosis

[jfheath]

An invaluable aid to the identification of electrical faults which result in the fuel pump not working on the ST1300. If you think that you cannot read an electrical circuit, try this. It takes you by the hand and leads you through the diagrams one step at a time.





The Fuel Pump Circuit has been the source of a number of electrical woes, and it is particularly awkward to work out what is going on from the main circuit diagram.

In fact, it is quite straight forward - a cascade of three individual relay circuits, each one turning on the next. A simplified version taken from the ST1300 Honda manuals is drawn above. The attached pdf file describes the circuit step by step, describes what the relays look like on the bike and how to determine which part of the circuit has failed. It even tells you exactly where to probe with your multimeter and what results you can expect if the circuit is working, and what to expect if it is failing.

Then there are 5 different scenarios or puzzles to get your brain around.

There are two versions attached, both identical, except that the left hand pdf has the answers on the back page; the right hand pdf has the answers at the bottom of each page.

 

[Whooshka]

Beautiful. You took about a thousand posts and condensed it here. Thanks so much!

ps. Wish I hadn't bought a new wiring harness about an hour ago.

 

[Ashley]

Excellent article. I hope I never need it.

Ashley

 

[ibike2havefun]

Another brilliant contribution from you, sir. I doff my topper in your direction.

I may have a need to study the article and diagrams in earnest, sooner than I would wish, as my bike has been showing greater and greater reluctance to start from cold. I'll post the rest of my commentary in the "ST1300 hard to start" thread to avoid pirating this one, but your salutary efforts here will make that process much clearer for me.

 

[Bmacleod]

This is really good information. I hope I never need it but saved the PDF in case. Thanks for the work and for posting it

 

[Chiefpep]

Hi John, @jfheath

You seem like an expert on the ECM of the ST 1300 and a 'go to' for my specific problem... I am from Amsterdam Holland and our ST forum isn't as experienced on the ECM issues that might be in case.

I am a pretty experienced technician if I say so myself, so you can talk 'tech' if you need to I maintain my ST 1300 very well, have no special things on my bike (one USB port that was allready there when I bought it and I added stronger light bulbs in the front and plug and play LED's in the rear).

All of a sudden a week or two my right blinking light started to act strange. Sometimes it flashed fast (probably one of the two bulbs stopped working) and the next ride it worked again... I thought: 'have to check those bulbs, probably bad connection or bulb needs replacement). Then, yesterday, I wanted to start the bike after a drive and the bike wouldn't start... The fuell pump didn't work. I mention the blinker light, because I read that the 'strange acting of blinking lights' is a common ECM problem on the ST which is hard to fix...

In my garage I tested everything that powers the fuel pump relay.

Pump works
Relay works
Wires are all closed circuit and perfectly working from the one end to the other.

Everything points to the black/white wires which get no power out of the ECM. Therefore the Relay of the pump gets no power.

The only thing I can imagine is that the ECM stoped giving the relay power because one or the other reason... All the other relays 'click' when turning on the ignition.

Is this a common problem? Do you hear this more often? As we speak I have sent my ECM to a specialized tester who do a diagnose. They are common with the ST ECM. In the meantime, I want to educate myself as much as possible in case it's not the ECM.

Thanks a lot!

 

[jfheath]

Thanks for the comments, but I am not an expert on the ECM. Far from it. I did the fuel pump circuit diagram because it is extremely difficult to follow on the Honda circuit diagram, and I had noticed that people on the forum were describing problems and attributing them to the ECM when I thought that the problem might be something completely different.

Like most people, I don't have money to throw around, and if I reckon that a problem may have a cheap solution or an expensive solution, then I will be wanting to make sure that I have eliminated the cheap solution before I spend money on the expensive solution!

My first comment is that the ECM rarely provides power to anything major. But what it does do is to activate devices which will provide power.

In the case of the fuel pump, that is activated by the 3 circuits that I mention in the pdf. The ECM does not provide power by the black and white leads, the fuel cut relay takes power from the b/w leads to provide power the fuel pump relay. If power is getting that far, then all it needs to power the fuel pump relay is for the brown lead to complete the circuit by connecting it to earth.

That final connection of the circuit to earth is the job of the ECM. Note that the ECM is connected to earth by wires, so if your grounding points are faulty or corroded or if you have issues with the multi pin ground connector then that may be relevant

But the ECM has other information to process before it will complete the circuit. Some of which involve other sensors and may involve the neutral switch, side stand switch and clutch lever switch. They also involve the HISS system if that is fitted - a distinct possibility if you are in Europe, but I am not sure. Your dash will have HISS on it if your bike is equipped.

Note that when testing the power to the fuel pump, the fuel pump springs into life for a couple of seconds when the ignition is turned on. Then the ECM turns it off. So performing any tests after that first two seconds will result in a diagnosis which is likely to be wrong.

If the pump doesn't whirr into life then there may be an issue with HISS. Fuses, faulty red kill switch (including forgetting to turn it on!), and incorrect key are typical suspects. If the system is working, the HISS light will go out after ignition has been turned on.

 

[Chiefpep]

Hi John. Thanks for your comprehensive and detailed reply! The ECM is on it's way to the tester. That's the first thing to do to make sure it's not the ECM unit. After that I will check on some more wiring looms behind the front fairing. I understood from several Dutch ST riders on our forum that some of them had the same and they found some faulty connections in the harnes in the front (left).

Regarding your suggestions in order:
- You make a difference between a fuel cut relay and a fuel pump relay... I only know of a fuel pump relay. Which one is the fuel cut relay? Do you mean the 60 degrees drop safety sensor in the front?
- ECM connected to earth by wires: Do you know where the ECM earths are grounded? Is that the notorious 'yellow earth block' which often is also corroded? (I believe also in the front?)
- The neutral switch is also something I hear more often. But the light is on when I try to start? And the motor turns? Is it dumb for me to say it therefore can't be the neutral switch?
- Side stand switch: If that would be the case, then the motor would not turn right?
- Same goes for clutch lever: The motor turn, just doesn't get fuel due to the pump that doesn't do the 'prrrrrrrr'
- Yes I have HISS. I know how it works. Tried the other key aswell. No luck.
- When I tested the pump (and relay) I did that straight with a 12V battery. And if I test it on the bike, I always turn off the ingnition afterwards. But good that you mention it.
- If HISS would be the case, would the motor and all relays work, accept for the fuell pump? You hear the other relays 'click' and I measure power to them. The only one is the fuell pump that doesn't get any power. Is the fuell pump the key 'anti theft' relay that makes the bike unusefull for thiefs? I would recon to do a kind of 'engine kill switch' effect that would totally kill the bike, not even able to have results by pressing the starter button?
- Same goes for kill switch. If that would be faulty or the case, the bike wouldn't try to run right? No reaction at all. That is not the case in my situation. It turns and turns, everything works, accept for the pump (due to the relay...)

Thanks again! I really appreciate it!

 

[jfheath]

Just answering questions.

Fuel cut / fuel pump ? I mean the same relay. I call it the fuel cut relay in the pdf.

The bike falling over is detected by the bank angle sensor, which will turn off the bank angle sensor relay. That prevent any power getting to the fuel cut relay / fuel pump relay.

I don't know where the Ecm is grounded. I spotted a couple of ground wires on the diagram. But the circuit diagrams are not an accurate representation of the physical configuration. They are a schematic. eg I dont think the multiway connector is shown on the official diagram, I've seen it on a multi coloured diagram - but the Honda just shows earth wires joining wherever it makes the diagram easier to read, rather than being connected together in one place.

The Bank Angle Sensor and relay are an early part of the fuel pump circuit, but from your description, I don't think that would be an issue. I covered how to test / where to probe in the pdf.

Side stand / neutral / clutch - easily tested. The bike will turn on the starter if the bike is in neutral.
It will not start if it is in gear and the clutch lever is out and the sidestand is down.

Careful testing the pump with 12v. You might end up putting 12v direct to the ECM if you have left it connected to the harness.
HISS. The ECM will probably kill all sorts of circuits, not just the fuel pump.
With a key without a matching chip, the engine will turn over on the starter motor but the engine will never fire.
With a proper key, turn on the ignition. If the pump whirrs and the HISS light goes out, all is ok.
I cannot remember whether other relays click on. I cannot check because I have a couple of other relays that come on with ignition.
I think my lights go on even if HISS isn't activated. Our lights are always on in UK.

I don't think that the fuel pump relay is the anti-theft device. I don't think that it is the only thing that is denied a complete circuit. I think the entire pulse generation, ignition circuits, timing and fuel management is all disabled.

Check the black / white wire voltage on the back of the fuel cut relay. There are two of them. check both. They should both read battery voltage ish. If neither show 12v, check the bk/wh lead terminal at the rear of the bank angle sensor relay. If that reads 0v then the fault is further forward - to the left in my diagrams.

If the bk/wh leads show battery voltage:

Check the brown wire to the fuel pump at the rear if the fuel cut relay. Wedge a probe alongside the terminal, and connect the other probe to earth. When you turn on ignition, that should read 0v because the Ecu has it connected to earth. Then after a couple of second, the Ecu turns off the connection to earth and it will read a bit less than battery voltage.

If this is as I describe, then the Ecu is doing its job. If it isn't as described, then swap the fuel cut relay for a working headlight relay and try it again.

Report back.

 

[Andrew Shadow]

Do you know if there were any fault codes stored in the ECM before you removed it?

If all wiring, connections, relays, HISS, etc., are good, if I remember correctly, there are only two failures that cause the ECM to disable the fuel pump;
- One or more inoperable fuel injectors.
- A defective camshaft or crankshaft sensor- I can't remember which one.
Either condition will usually register a fault code.

Are mice plentiful in your area? Check for damage to the wiring harness under the throttle bodies.

 

[Chiefpep]

@jfheath Thank again for your extensive answer.

You've done a great job by simplefying the diagram. I've done kind of the same in my (almost best viewed) Youtube series about wiring. Seems like bike manufactures like to present things a bit more complicated then necessary

I've tested the bank angle sensor just in case. Works perfect, but couldn't be an issue indeed. Same goes for the side stand / neutral / clutch switches. They would all show other symptoms if one of those were broken.

Indeed I've tested the pump and relays outside of the harnes. So the ECM wasn't connected at all. Thanks for the heads up.

HISS is all good. Works as it should. Including lights and all. We (in Europe) have the same bikes. Lights always on, no switches to turn them off. And HISS in all the bikes.

The black/white wires were the last I tested and the reason why I've send the ECM out for a checkup. If I understand the wiring diagram well, they both should give me 12V as soon as I turn on the ignition key. They are fed out of the ECM. They don't give me this (neither of them) but they are a closed ciruit whey I measure from the ECM connector to the connector of the relay. So the wires are good, not broken anywhere, they just don't give me voltage. Not even a second.

Also, Brown doesn't give me positive either. Also the wires are ok (when I measure if it's closed or not from front to back). I don't really understand 'Wedge a probe'... That's a bit insider English and I'm still Dutch... Sorry

To change or swap the relay I don't really think that's nescessary since all measures and tests turn out it works fine...

@andrew I don't know if there are any fault codes. The ECM is on it's way to the tester as we speak (write). We don't have mice here... But, the very first thing I will do is check the harness and especially in the front at connectors and bundles and offcourse the notorious ground distribution bus...

Thanks again all! I will keep you posted!

 

[woodybelle]

The black/white wires were the last I tested and the reason why I've send the ECM out for a checkup. If I understand the wiring diagram well, they both should give me 12V as soon as I turn on the ignition key. They are fed out of the ECM.
[/QUOTE]

This is not right. The ecm does not provide 12v on the black/white wire. The black/white wire comes from the fuse block. The ecm only grounds the fuel cut relay with the brown wire.

 

[Chiefpep]

According to my Haynes Workshop manual, the wiring diagram in the back, the black/whit does come out of the ECM (to be precise, the 4th pin on the grey 26 pin connector). And, it practice with my test, it also gives me a closed circuit from that pin of the ECM and the pin of the connector which goes on top of the fuel cut-off relay...

 

[woodybelle]

Are we all assuming that the diagram in the first post is correct? It does not show a black and white wire from the ecm to the fuel cut relay. Also the ecm grounds the fuel cut relay, it does not supply 12v.

 

[jfheath]

Answers below are in preparation.

The black/white wires were the last I tested and the reason why I've send the ECM out for a checkup. If I understand the wiring diagram well, they both should give me 12V as soon as I turn on the ignition key. They are fed out of the ECM. They don't give me this (neither of them) but they are a closed ciruit whey I measure from the ECM connector to the connector of the relay. So the wires are good, not broken anywhere, they just don't give me voltage. Not even a second.

The Bk/Wh leads connect the 12v power out of the Bank Angle Sensor Relay to the power in to the fuel pump or fuel cut relay. The same source also supplies the trigger to the fuel cut relay to turn the relay on.
That lead is Not connected to the ECM. Not in my diagram, not in my Honda diagram and not on my bike.

Are we assuming that the diagram is correct ? It as a very valid question and one that should always be asked of information found on the internet. All I can say is that I had the relays off the holders to take photos of the rear of them, and I verified all of the observations that I reported with voltage and continuity tests. This was using a honda circuit diagram for a 2004 UK ABS model which was checked on my current ST1300A9 - manufactured Sept 2013. I also compared with the diagram produced by Anna's Dad and the other diagram that is available on this site - the only one that shows the multiway earth connectors.

It is as correct for this model bike as it is possible to be.
(except as stated in the pdf, I have over simplified the behaviour and wiring of the bank angle sensor)

Also, Brown doesn't give me positive either. Also the wires are ok (when I measure if it's closed or not from front to back).

The brown lead will only give a positive reading if the fuel cut relay is turned on, and that requires power on the black/ white lead. You say that you don't have 12v on the black white leads, so the fault has got to be before the fuel cut relay. To the left of it in my diagram.

So you will need to check what is going into the bank angle sensor relay.

Note the comment that the bank angle sensor is not a switch as shown in the diagram. It is an electronic device which normally gives a low voltage output. There is enough of a potential difference to allow current to energise the coil to switch on the Bank relay and allow current to flow from the bk/wh wires. Its not likely to be faulty. The real question is whether you have battery voltage on the ppl/bk wire going into the relay and battery voltage on the bk/wh leaving it.

I don't really understand 'Wedge a probe'... That's a bit insider English and I'm still Dutch... Sorry

Sorry. Your English is so good that I forgot that you are dutch.

At the rear of the relays there are four leads with coloured wires. The have brass terminal which slide onto the spade terminals of the relay. Most multimeter testers have two leads with a thin insulated metal spike. This is the 'probe' that I am referring to. It is possible to insert the pointed spike / probe down the side of the terminal, and it will be lightly trapped. (A wedge is a piece of wood / metal / cheese that is wider at one end than it is at the other. Hammer it into a gap and it will squeeze in until it gets trapped. It is 'wedged' into the gap.). I was suggesting that if you put the multimeter probe down the side of the appropriate terminal at the back of the relay, it will stay there, leaving your hands free to turn on the ignition and watch the multimeter reading for the two seconds that the relay should be turned on.

 

[woodybelle]

The real question is whether you have battery voltage on the ppl/bk wire going into the relay and battery voltage on the bk/wh leaving it.

That is it in a nutshell John. I might add that the ppl,bk wire is fed from fuse L in the rear fuse block. Also the bk/wt wire at the ecm is an input from the bank angle sensor not an output to the bank angle sensor, I think Cheifpep has this mixed up.

 

[jfheath]

I have just been re-checking this. The purple/black lead provides the main 12v feed direct from the fuse to the bank angle relay. If the bike is not in its side, that turns on the feed to our black and white leads. In fact there are lots of bk/wh leads, all connected together in a multiway connector. One of these outputs powers the fuel cut relay. Others power the injectors, the coils and various other devices, including the ECM. The ECM is a computer and it requires power. So yes, there are bk/wh leads connected to the ECM, but not as a functional part of this particular circuit.

If you received an email notification of an earlier posting, and are wondering where it is - I thought I had better check it out first, so I deleted it. In fact, it was perfectly Ok.

 

[Chiefpep]

Well, I'm talking about these... And perhaps I am wrong that the ECM provides 12V via the black/white... But the fact that the rest that these wires supply maybe I presumed it... In any case, the ECM isn't here at this moment, so I can't really test or measure anything right now. I will continu as soon as I have it back, or know rather it's ok or not.

 

[mjc506]

That line is a switched ground - when 'running', the ECM internally connects it to ground (battery negative), when not running, it's open/floating and no current will flow (and will read 12V due to the connections with other components).

 

[Chiefpep]

A brief update. Received message from my ECM tester. ECM is okay. So, today I continue to measure wires, ground, switches and relays. Of course with an update as soon as I have found something (or nothing...)! It's a shame, of course, that I'm going to do this without a connected ECM, but nevertheless I can do a lot in advance. Update you soon!