Dreaded ECU Issue

David Currie

Joined
Jul 9, 2023
Messages
2
Age
62
Location
Western North Carolina
Hello Everyone! I own a 2003 ST1300 ABS model that I purchased used from a good friend last year. Love the bike and have enjoyed unwinding the curves up here in the western North Carolina mountains! A couple months ago, I noted the F1 light came on and went through the evaluation process - ultimately landing at a local Honda dealer. He told me it was throwing a knock sensor code, but he has seen that a faulty ECU has been the culprit more often than not. Given the high price tag of a replacement ECU, I chose to replace the sensor - to no avail! The F1 still keeps shining! Seems like this is a common problem/post for pre-2008 bikes of this ilk. My question is as follows - if this is a faulty ECU process that doesn't seem to affect performance noticeably, has anyone just continued rolling the dice and riding?!? I guess my suspicion is that the ECU issue appears to be predominantly related to sensing knock sensor status, not other critical functions of engine performance. Admittedly, this may be naive and wishful thinking, but I have also been unsuccessful at finding a replacement ECU anywhere (currently unavailable on Partzilla)! I appreciate any constructive feedback or experience with this topic (or leads on a replacement ECU). Many thanks.

D. Currie
 
Hi, they are several posts about this issue.
I had the same problem in my 2006 St.
The first test you can do is switch sensors because code 25 is for one side and 26 for the other side.
In my case after switching the sensors it continued showing the same problem therefore I knew it was not the sensor.
First, try to reset the FI, after that when you reach more than 4K rpm in the tach if the light of FI goes on, you must replace the ECU.
There are other suppliers of ST parts with better prices.
Good luck.

How to clear the FI codes on st1300
1- Put the bike on the center stand
2- Put the side stand DOWN
3- Put the red kill switch ON

Don't touch the accelerator at any moment.

4-Put the key switch ON
5- With only your finger PUSH the start switch
6- Wait until you have the 3 bar temperature

7- STOP the engine with the ( red) kill switch
8- Put the key switch OFF
9- Go to the left side and put the side stand UP

This procedure will clear the FI codes.
 
leonides said:
Hi, they are several posts about this issue.
I had the same problem in my 2006 St.
The first test you can do is switch sensors because code 25 is for one side and 26 for the other side.
In my case after switching the sensors it continued showing the same problem therefore I knew it was not the sensor.
First, try to reset the FI, after that when you reach more than 4K rpm in the tach if the light of FI goes on, you must replace the ECU.
There are other suppliers of ST parts with better prices.
Good luck.

How to clear the FI codes on st1300
1- Put the bike on the center stand
2- Put the side stand DOWN
3- Put the red kill switch ON

Don't touch the accelerator at any moment.

4-Put the key switch ON
5- With only your finger PUSH the start switch
6- Wait until you have the 3 bar temperature

7- STOP the engine with the ( red) kill switch
8- Put the key switch OFF
9- Go to the left side and put the side stand UP

This procedure will clear the FI codes.
Click to expand...
So it appears replacement of the ECU is the only reasonable option, given that the dealer shop cleared the F1 codes after replacing the knock sensor and it still came back. Does anyone have contact information for parts suppliers that have the 38770-MCS-L01 ECU in stock? Everywhere I have checked so far indicates the part is discontinued/out of stock/unavailable! Thanks again for helpful information.
 
I think I remember someone saying in another thread that you can simply ignore the light and continue riding. Probably best if you PM @Igofar and ask him. I also remember discussions saying that the ECU's are as plentiful as hen's teeth. In fact there is another thread going right now...

Wanted - Still looking for a ecu | Buy/Sell/Wanted

Still looking for a ecu have the old code 25
www.st-owners.com www.st-owners.com

Good luck.
 
SMSW said:
I think I remember someone saying in another thread that you can simply ignore the light and continue riding. Probably best if you PM @Igofar and ask him. I also remember discussions saying that the ECU's are as plentiful as hen's teeth. In fact there is another thread going right now...

Wanted - Still looking for a ecu | Buy/Sell/Wanted

Still looking for a ecu have the old code 25
www.st-owners.com www.st-owners.com

Good luck.
Click to expand...
@Igofar does not recommend ignoring the light, or continuing to ride it. If my memory serves me correctly.
 
May not have a choice at some point... as the bikes get older and they fail they'll be even harder to find... we need an EEE to open one up and see if a component can be repaired... THAT would be a nice small business and many will buy one just to have handy.
 
I'm keeping an eye out for a failed one in the UK/EU. HISS will make things tricky to test unfortunately :-(
 
The Part # you need is

PGM-FI UNIT

38770-MCS-L01
None of the known parts sellers has it in stock.
They are several used ones in stock on eBay, you can ask if they do not solve the problem if they can be returned it.
If the bike where they took it from was in an accident, you may be lucky.
There are some on Amazon, brand new.
If you are going to bite the bullet do not waste any time.
I don't know if any other years will do the work. Maybe a police unit will do.
Maybe the electronic guys know.
There is or was a Co. in Broward, Fl who was trying to find a cure for that.
They will ask you to send the damaged ECU, and they will use it as a guinea pig, but if they will find a solution they will not return it to you.
Not a big deal.
When I had this problem I notice that the MPG reading was not right. , besides that who knows?
 
Last edited:
You could temporarily disconnect the knock sensors and see if the F1 light comes on.
 
I got a 2003 as well and when the F1 light came on I cleaned the 5way tee as described by Igofar, and light gone.
Easy fix for me, and I’m barely average experienced…
Stu
 
Larry Fine said:
Shouldn't the sensor harness be eliminated as the cause first? I remember reading that it melts.
Click to expand...
I bought a 03 recently and it has melted connector on rt knock sensor.has stored code 26.No check engine light was on during 40 mi road test.Im not so sure you all Need new ecu.More likely Bad circuit between sensor and ecu.You could run new overlay circuit as a test
 
vstrom.zrxdude said:
I bought a 03 recently and it has melted connector on rt knock sensor.has stored code 26.No check engine light was on during 40 mi road test.Im not so sure you all Need new ecu.More likely Bad circuit between sensor and ecu.You could run new overlay circuit as a test
Click to expand...
It's hit or miss... some have replaced a lot of components and still get the code. Unfortunately, that code can be what it says but also the failure of the ecu itself. No one has yet to provide a service to restore an ecu.
 
Mellow said:
It's hit or miss... some have replaced a lot of components and still get the code. Unfortunately, that code can be what it says but also the failure of the ecu itself. No one has yet to provide a service to restore an ecu.
Click to expand...
I'm pretty sure that if some electronic wizard put some time into trying to solve the problem of repairing a damaged ECU he will find a cure.
Let us pray.
 
The knock sensors are just microphones. The ECU doesn’t listen for no noise, it only listens for a knock via the sensors. A short would indicate a knock. An open circuit would indicate no knock. If the ECU hears a persistent knock it defaults to limp mode to get you home.
 
Eh, sort of. The sensor themselves are piezo transducers, so vibration (more accurately, flexing them, but the deflections are tiny!) produces voltage, so the ECU will either be measuring peak or RMS voltage, maybe frequency (not sure there's sufficient computing power in there for FFTs, so more likely voltages) and backing off the timing if it detects high voltage (caused by a knock, or any other 'knock-like' vibration). I can imagine feeding peak or rms voltage into an ADC and comparing it to 'good' values depending on rpm and load - too low a reading could also indicate issues with the knock sensor. But that's a guess really, I've not opened up one of these ECUs yet, let alone REd the firmware.
 
Most people don’t know what piezo transducers are. So.. :) Perhaps I should have said piezoelectric microphones.
 
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