C28 / STVA problems

[crisis]

Hi,

I have a problem with my SV650SK6. Since I got it a few months ago the FI light has come on intermittantly, always with code C28. Most of the time it's ok riding with the code, although sometimes it's very low on power (presumably the secondary throttle valve is closed). A couple of times it's felt quite dangerous, once trying to get up to speed with lots of traffic around and once having to abort an overtake. Sometimes the code disappears while I'm riding along, mostly I stop and turn off/on to try to clear it. I've not had the symptom other people have described of the bike revving with closed throttle.

If I remove the airbox and turn on the ignition sometimes the self-check (STV full open then partial open) works fine, but other times it just messes around opening and closing or "quivering". Sometimes the self-check seems to work ok then after a few seconds it starts moving back and forth a little bit.

I've checked according to the FI system diagnosis PDF, as far as I can see everything checks out. I'm not entirely sure how best to check for poor contacts in the connectors, I've tried checking resistance of the STVA from the ECU connector and that seemed ok. Also tried adjusting the STV position sensor in case this could cause the issue but that didn't seem to help. If the STV position sensor was out I'd also expect that to give a different code.

I asked an independent dealer to take a look while they had the bike for something else but they recommended that I either take it to a Suzuki dealer or change the STVA. Based on the cost of second-hand throttle bodies vs. cost of labour, I bought some TBs off eBay, but the same thing happens with these, or at least the self-check is still messed up.

The only things I can think of from here are:

1. Give in and take it to the Suzuki dealer.
2. Buy a second-hand ECU from eBay and give that a try.
3. Splice in a new set of wires from the STVA connector to the ECU.

I know this is an issue that's come up before, but I've not found any threads that match my symptoms where there's a solid conclusion. Apologies if I've missed one.

Does anyone have any suggestions before I start throwing more money at this...? Can Suzuki dealers test the ECU somehow? Has anyone seen this problem caused by a faulty ECU?

Cheers,

Ben

[Sid Squid]

If you've checked continuity of the relevant wires and security and condition of connectors, and found no problem then it would seem that there is a component problem, but bearing in mind that wiring and connector faults account for the overwhelming majority of electrical and electronic problems that I am presented with, in your position I would make utterly certain that all those parts are tip-top before spending money on possibly un-necessary parts. After that, is it possible that you could find a friendly forum member whose ECU etc. could be substituted to identify the problem?

[crisis]

Thanks for coming back to me so quickly. It sounds like I need to check the connectors again more thoroughly. I'll test the resistance of the STVA from the ECU connector again, as I'm guessing that should be a good test of the two connectors near the STVA. I'm less certain of how to test the ECU connector however.
If any of these connectors are at fault, is there any way to replace them, or is it a matter of trying to bend the terminals to get a better connection (or a new loom)? I can't see any obvious corrosion, but I will check that again as well.

I wondered about checking the output from the ECU with the ignition on (e.g. needle probes from the back of the connector) but I'm guessing it may not be easy to measure using just a multimeter?

Cheers,

Ben

[Red ones]

What's the weather like when it happens? It doesn't happen to be damp by any chance?

Also does it ever hold the revs too high when you are riding? (Which is scary if your going in to a corner as the guy I know was at Snetterton!)

[Sid Squid]

There is - I think - a voltage check across the STVA, I'll look it up.

[Red ones]

I have only just spotted the comment "Splice in a new set of wires from the STVA connector to the ECU"

Have you spotted the connector on this line? It's a small black box. I'd open it up and check the state of the connections in there, for what it's worth.

[crisis]

I generally only take the bike out when it's dry, and it's been sat in my garage for about a week, so unless it's some trapped moisture I don't think it's damp. I may try blowing the connectors out with an airduster tomorrow though, just in case. The guy who owned it before me used it in all weathers I think, which may explain the less than ideal condition.
I've certainly not noticed it holding the revs too high, although I did note other people had said theirs did that. I must admit I was confused as to how that could happen - one set of throttle butterflies is controlled by the rider, so surely shutting that will close off the airflow even if the STV is wide open? I may be missing something obvious here...

So in terms of connectors I've looked at, there's the one that connects to the STVA itself, then a connector from the STVA-and-injectors sub-loom to the main loom, then the connector from the loom to the ECU. Am I missing one...?

Sid - thanks for taking a look.

[Sid Squid]

Disconnect the plug at the servo, and on the servo's terminals check for continuity between the terminal that the red/black wire connects to and a convenient earth point, there should be none. Then check resistance across the two terminals of the servo, which should be between 7 and 14 ohms. Reconnect the servo plug and disconnect the ECU connector and do the same checks at that point - red/black wire to earth and across red/black to black/red wires. Obviously this should give the same results as at the servo, if it doesn't then there's a wiring/connector fault.

[crisis]

Ok, so as far as I can tell there's no continuity between that terminal and earth. Resistance across the servo is around 10 ohms, and it's similar when tested at the intermediate connector and at the ECU connector (slightly higher resistance moving away from the servo). I tested a couple of times and the numbers varied slightly (less that 1 ohm) but this may have been down to the connection from the multimeter probes to the connectors.

Once I'd reconnected it all back up, I turned the ignition on and the STV was moving about all over the place, back and forth, definitely not the normal self-check movement. No C28 code though, just various other codes which I assume are because the airbox is off.

Just to check I'm not being a complete idiot, the throttle bodies are sitting loose at the moment, as I wanted to test before I reattached them, and because it's a lot easier to access the servo terminals. I'm thinking this should be ok, because they're connected via rubber normally i.e. not earthed?

Anyhow, based on these results my best guess is that either the ECU connector terminals aren't contacting the ECU pins properly, or the ECU is bad. I'll have another check tomorrow evening if I get time.

[Red ones]

Sounds like the problem I had last year.
http://forums.sv650.org/showthread.php?t=201511

Eventually I sold the bike, but the next owner fixed it. The cabling from the STVA was corroded in a connector block.

[crisis]

I think I may have made some progress with this today, although I'm now unsure if there's one problem or two.

I did the same checks of the STVA wiring again, and again couldn't find an issue. The ignition-on STVA check was all over the place, as before. Still no C28 code with the ignition on though.

I'd already checked the resistance of the STV position sensor at the connector, with the STV open and closed, but I thought I'd perform the same check from the ECU connector. I found the relevant terminal easily enough for the yellow wire, but I couldn't get continuity from the black wire to any of the terminals. At this point I was questioning my reading of the wiring diagram, but then I found those two little connector blocks on the left of the bike near the frame that don't go anywhere. I noticed that one had black and brown wires leading into it so I opened it up and apparently it's just there to join all the wires going in via a jumper.
A couple of terminals in that connector were a bit corroded, although not too bad. In any case, I removed the jumper, sprayed contact cleaner in there and put the jumper back. Bingo - continuity from the black wire to one of the ECU pins, and more importantly the STVA self-check works perfectly now.

The question remains as to whether this could cause the C28 while on the move, and why it wouldn't give a C29 error if the ECU got a faulty signal from the STV position sensor. This is why I wonder if I also have another problem that's causing the C28. In any case, I've put it all back together and will take it out for a ride when I have time, to see if the error crops up again.

If that has sorted it out that will be very satisfying, it's taken me a long time to get to this point.

[crisis]

Two (shortish) rides since cleaning up the jumper connector, no FI light or C28 code so far...

[crisis]

Just an update to this one for anyone searching for this problem, I've not had the problem at all since cleaning up the jumper connector, including on a few two hour rides.

So, if you have the FI light and C28 code, obviously go through the troubleshooting steps from the workshop manual (downloadable somewhere), but if there's no obvious circuit problem, before you replace the throttle bodies or ECU, try checking the STPS (secondary throttle position sensor) resistance from the ECU connector (carefully!).
If you can't get a reading and there's no continuity from one of the STPS terminals to the ECU connector, have a look at the odd little connectors that go nowhere near the frame on the left hand side. If there's corrosion in there, take out the jumper and clean it and the connector until you have continuity. Next check that the STPS resistance varies as it should when measured from the ECU connector, and hopefully this should resolve the issue. If not, the problem lies elsewhere.

[Bibio]

the connector you are on about are negative (earth) clusters.

[crazy_sailo5878]

Hi

Where exactly is the negative earth cluster?

I'm having trouble with my STVA, it doesn't move at all except the occasional twitch. I have checked continuity to ground and have infinity, resistant between terminals is 16 Ohms at the STVA connector, plug just down from the connector and at the ECM terminals.

Is there any other way I can check the function of the stepper motor ie what voltage are the pulses?

Many thanks

Gaz

SV650 K5

[crisis]

Hi,

From memory they are near to the frame on the left hand side i.e. just underneath the tank. They look like connectors that go nowhere, and should be covered with a plastic cover.
However, if you get the same resistance at the ECU connector then I wouldn't suspect an issue with the earth block for that circuit.

Have you tested your STPS? My issue was with this, not the STVA wiring. You quote some of the tests so I assume you have the FI system diagnostic pdf. The tests for the STPS are under code C29 I believe.

I'm not convinced you'd be able to check the voltage supplied to the STVA using a standard multimeter - as you say, they're pulses so the multimeter won't react in time. If you have some form of data logging multimeter that may work I guess. If your STPS or associated wiring is bad though, I guess you'll still get bad results.

[crazy_sailo5878]

Crisis - Many thanks for your reply but I found the solution to be far simpler than expected- http://forums.sv650.org/showthread.php?t=220760


Once I had fixed it I was too excited putting things back together and forgot to take measurements of the signal to the motor. If it fails again or if I have time I may try taking some readings as I'm not convinced that it is actually a stepper motor on that particular model but rather a standard DC motor. Although I'm not going to lose sleep either way, just for my own curiosity.


Thanks again.


Gaz