Knock Sensor Issue

tranquilokj

tranquilokj

Joined
May 20, 2006
Messages
8
Age
62
Location
Gurabo, PR
Bike
2005 ST1300A
I have been working this problem for a while and have not corrected it. My 2005 ST started giving me a code 26 on the F1 lamp. I went to the service manual and it indicated a malfunction with the right knock sensor.

I performed the first part of the diagnostic to determine if the sensor was at fault. I found some information on the manual that did not make sense. It tells me to look for continuity between the knock sensor wire and a terminal at the computer. If there is continuity, that there is a problem with the harness. I went over the wiring diagram and found that there is nothing in between the sensor and the computer, so if there cannot be any continuity; how does the knock sensor communicate with the computer?? Nevertheless I did find continuity, so in my brain I was satisfied with my analysis, not Honda's.

Since the connector at the knock sensor broke in my hands while removing it, I thought that it could be the problem. I ordered the knock sensor and the partial harness (major pain to install, about 6 hours). After installing the sensor and the new harness section (the one covers both knock, oil pressure, temperature sensors and the neutral switch).

I went riding and the light came back on. I had forgotten to re-set the computer, so this must be it. I proceeded to re-set the computer and went riding again last weekend. My F1 lamp came back on!! Needless to say I am very frustrated with this. Furthermore I cannot ignore the lamp while riding, not to mention the decreased performance and additional fuel consumption I'm getting.

Any suggestions??

Jeff:confused:
 
I wonder if the connector on the engine block has some corrosion on it that might be interfering with the signal.
 
I went through the exact same thing..Only difference being the code 2-5, left knock sensor..

I too did the same checks and made the same assumptions about the service manual verbiage as you did, Yep there was continuity all the way to computer on both left and right sides. I first checked, cleaned all connections,(used die-elec grease) double checked grounds, made sure no pinched wires etc (had the bike all tore apart at one point), would get the FI (solid not flashing)light anywhere between 10-40 miles of riding, pull code 2-5, clear codes, no light till I rode it etc.

I did replace the left sensor (had to cut down a deep socket to get that guy out without pulling exhaust etc).

I found the wire to the right sensor close to failure and made the repair on it
too
So far, several 300-400 miles rides, no light, gas mileage has shot back up and engine runs great.

I thought I was the only one who has suffered this...mine is a 2003 with 50k miles.

Other than a ground issue, I don't have any additional suggestions...yet... well possibly one..swap the physical sensors, put left in right position and right in left...if the problem moves then it could be a sensor issue (i know you said you replaced right sensor already) perhaps problem is really left? perhaps mine was really the right and repairing the wire fixed it?
 
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What grounds did you clean? I replaced the harness portion on the engine. I will check the connection point behind the engine like Mellow suggested. It looked clean to me. It's going to take a few weeks, I had this whole bike apart and I got to get in the mood again. Thanks for your input.
 
tranquilokj said:
...I found some information on the manual that did not make sense. It tells me to look for continuity between the knock sensor wire and a terminal at the computer. If there is continuity, that there is a problem with the harness. I went over the wiring diagram and found that there is nothing in between the sensor and the computer, so if there cannot be any continuity; how does the knock sensor communicate with the computer?? Nevertheless I did find continuity, so in my brain I was satisfied with my analysis, not Honda's.
Click to expand...

I agree, the test in the manual states:

Service manual section 5-47; said:
Check the continuity between the right knock sensor 1P connector terminal and ECM connector.

Connection: Red/blue - Red/blue

Is there continuity?

YES - Open circuit in the Red/blue wire.
NO - Faulty right knock sensor.
Click to expand...

Which is incorrect. They have the YES & NO answers swapped. If there is continuity, the only option left to do is to replace the sensor. If no continuity you have the open circuit. They make the same mistake for the left knock sensor open circuit inspection also.

The wiring diagram in my copy of the service manual sucks. Many of the circuit traces in the diagram don't line up properly and with the small size of the diagram it makes it next to impossible to read. I would suggest going over to this site here to download one of the PDF versions of the Setup Instructions. Each one has a wiring diagram for both the Standard and ABS version of the bike. Once you look at a good copy of the schematic you will see that there is a wire that runs from the knock sensor to the computer.

I did notice that the wiring diagram posted in the 2008 Setup Instructions has been updated to add better descriptions and pinouts to the computer and dash diagrams. They have also made the traces thicker which makes it more difficult to read!:mad:

In the wiring diagram I notice that color of wire for the Left Knock Sensor is supposedly BLACK but the service manual diagnostic section on page 5-46 implies that the color is BLUE... whats with that???

The other observation I made in the diagram is that for both the left and right knock sensor connections by the computer they show a trace running from each wire to a G/P (green/pink) wire. [This wire connects to the A23 connector of the harness which is for PG1] The thing that I'm not sure of is that there is the letter "S" shown in these shorting wires and I'm don't have a clue as to what that represents???

I would echo the previous post that suggested swapping the left and right sensors. It might give you some clues. Perhaps the manual has them backwards? Is the wire color for the right side knock sensor Red/blue? Also looks like there is a shield around the right side knock sensor but not around the left. Did you replace the correct one (I don't mean that in a demeaning way).

Keep us posted!

Good Luck!
 
I have checked all the manual's references for the right side of the bike, just in case. I did replace the one with the metal shield (right side), but I do recall that the wire color was not what the manual indicated. I will try the swap next (take out the tupperware...again) and check all intermediate connections. I will also double check the connector in the computer. It fits kind of tight in its location and it could be causing a poor connection. Any other suggestions are really welcome. Thanks guys!
 
Well Crud, about a thousand miles since I thought I had it fixed my 25 error is back..

I think I am going try removing that wire from the connector and see what that does.

I am not real sure how that circuit/sensor inputs to the computer. One wire to the sensor must mean that ground comes from the engine block?

Anybody know how a knock sensor works? Must send/or take away some sort of signal voltage to the computer (either 12v or 5 volt logic signal?)

Guess I will google knock sensors and see if I cant learn about them and the logic that drives them.

ARRGGG.
 
Dketchum said:
Anybody know how a knock sensor works? Must send/or take away some sort of signal voltage to the computer (either 12v or 5 volt logic signal?)

Guess I will google knock sensors and see if I cant learn about them and the logic that drives them.

ARRGGG.
Click to expand...

I believe it's a piezoelectric device. Which means a crystal that give off a changing current when its surface is compressed or expanded or vibrated.
I have read where tapping on the engine block will cause a noticeable change (in some vehicles) in the engine due to the knock sensor varying the timing.

The symbol on the diagram does seem to be a piezoelectric device. As for the wiring it appears the wire is shielded. This is common on devices that have very small voltage or current, and prevents induced signals from affecting the circuit. Also notice on the diagram there is a jumper passing through the intermediate connector and at the ECM end a wire from both knock sensors are tied together into the ECM and then on to a ground. This is the shield being grounded on the ECM end, and I believe this is why it's marked (s). Shields are always grounded on only one end to prevent ground loops (more induced signals). Having said all that here is what you have:
1. One wire running from the Sensor to the ECM
2. The sensor is grounded through its own case to the block.
3. Under the cover of the wire is the shield. A conductive mesh or foil (like on a TV coax). This shield isn't and should never make connection with the main wire inside. The shield is connected to ground on one end only with the other end open. The shield needs to be a complete circuit all the way from the knock sensor to the ECM where it is then grounded. This is why the diagram shows a jumper going around through the intermediate connector to complete the circuit for the shield. Showing it the way they do is misleading and makes you think its part of the knock sensor wire.

To check the circuit out you need to make sure the knock sensor wire has continuity from the sensor to the ECM. Then you need to connect your ohmmeter to the shield at the sensor and make sure it's grounded. Then read from the knock sensor wire to the shield and make sure you don't read continuity.

I worked on Jet A/C wiring for over 38 years and found many times that a shielded wire chaffed through and came in contact with the shield. This of course would ground the circuit at that point. One way you could make sure the wire isn't grounded to the shield would be read to ground. This is the test mentioned in the manual where you connect the meter to the sensor connector and ground. If you read continuity to ground it might to be coming from the shield.

I believe I'm right, but motorcycle wiring diagrams really suck compared to aircraft w/d and I am making some assumptions.
 
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curmudgeon said:
I believe it's a piezoelectric device. Which means a crystal that give off a changing current when its surface is compressed or expanded or vibrated.
I have read where tapping on the engine block will cause a noticeable change (in some vehicles) in the engine due to the knock sensor varying the timing.

The symbol on the diagram does seem to be a piezoelectric device. As for the wiring it appears the wire is shielded. This is common on devices that have very small voltage or current, and prevents induced signals from affecting the circuit. Also notice on the diagram there is a jumper passing through the intermediate connector and at the ECM end a wire from both knock sensors are tied together into the ECM and then on to a ground. This is the shield being grounded on the ECM end, and I believe this is why it's marked (s). Shields are always grounded on only one end to prevent ground loops (more induced signals). Having said all that here is what you have:
1. One wire running from the Sensor to the ECM
2. The sensor is grounded through its own case to the block.
3. Under the cover of the wire is the shield. A conductive mesh or foil (like on a TV coax). This shield isn't and should never make connection with the main wire inside. The shield is connected to ground on one end only with the other end open. The shield needs to be a complete circuit all the way from the knock sensor to the ECM where it is then grounded. This is why the diagram shows a jumper going around through the intermediate connector to complete the circuit for the shield. Showing it the way they do is misleading and makes you think its part of the knock sensor wire.

To check the circuit out you need to make sure the knock sensor wire has continuity from the sensor to the ECM. Then you need to connect your ohmmeter to the shield at the sensor and make sure it's grounded. Then read from the knock sensor wire to the shield and make sure you don't read continuity.

I worked on Jet A/C wiring for over 38 years and found many times that a shielded wire chaffed through and came in contact with the shield. This of course would ground the circuit at that point. One way you could make sure the wire isn't grounded to the shield would be read to ground. This is the test mentioned in the manual where you connect the meter to the sensor connector and ground. If you read continuity to ground it might to be coming from the shield.

I believe I'm right, but motorcycle wiring diagrams really suck compared to aircraft w/d and I am making some assumptions.
Click to expand...

Thanks for that very elightening post...I now understand the whats and hows..now to go figure the why. :eek::
 
If you aren't familiar with shielded wire there are photos on this site along with some termination techniques:

http://www.aeroelectric.com/articles/pigtail/pigtail.html

Note the shielded wire is made up of:

one or more insulated conductor(s)--- surrounded by a metal mesh or foil conductor--then the shield is covered with an insulated sheath.

I didn't initially realize the Knock Sensor wire was shielded as it's normally drawn with a circle around the wire. Looking at the Honda diagram I believe this wire is shielded even though they don't follow proper wiring symbol protocol. This website shows how it should be drawn. Look at page 40 for shielded wires:

http://books.google.com/books?id=0o...CcF7&sig=ObBWvpu4PmVJwbFQNe6lcfdjlCc#PPA40,M1


I also noted shields are always grounded on one end only. This is generally the case but not always. My experience with Boeing and Douglas A/C is was the case most of the time.
 
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I went and researched Honda knock sensors in general and there seems to be a common theme...The ECU is always looking for an output from the sensor(piezo-electric) it would/(could be around just 1-1.5 volts which is produced through normal harmonics with the engine running etc..Knocking causes an increase in voltage, seems to be a 3V threshold or so thus producing a retarding of timing.

If there is no output(or not reaching the ECU,) then the code will be set.
So just unhooking the sensors isn't a solution..
 
Dketchum said:
I went and researched Honda knock sensors in general and there seems to be a common theme...The ECU is always looking for an output from the sensor(piezo-electric) it would/(could be around just 1-1.5 volts which is produced through normal harmonics with the engine running etc..Knocking causes an increase in voltage, seems to be a 3V threshold or so thus producing a retarding of timing.

If there is no output(or not reaching the ECU,) then the code will be set.
So just unhooking the sensors isn't a solution..
Click to expand...

Dave, where did you find this info?
 
curmudgeon said:
Dave, where did you find this info?
Click to expand...

Well, I searched on Honda Knock sensors and it produced a lot of hits from Honda car enthusiast forum discussions about knock sensors..through all the discussions I read I was able to get that information..granted it is in reference to Honda cars (mostly civics) but I would highly suspect that Honda wouldn't re-invent or make major changes to adapt to the motorcycle.
Saves them $$.
 
Hi man i am Huckson from singapore i am currently riding a 04 stx ,2 years back i suffer tha same problem like yours right knock sensor FI blink 26. I ve spend months finding the problem to my suprise the problem is not from the sub wire hardness or knock sensor.Try this hope that it will resolve your issue. 1) remove your left cowl 2) you will see the sub wire hardness connected to the main wire hardness. 3)clean each connecters with anti Corrosion solution Note Do not used WD40 .4)Apply Heat sink compound ( Mostly use for processors on computer eg. Dow Corning 340. 5)Assembly the sub wire connecters to the main wire connecters. 6) Testing, place your bike on its center stand, warm up your bike when its done rev and hold the Throttle to rpm 4000 see if the problem persist if its Yes Repeat sept 1-6 If no Cheers. thats all i ve got to share.:04biker::)
 
curmudgeon said:
I believe it's a piezoelectric device. Which means a crystal that give off a changing current when its surface is compressed or expanded or vibrated.
I have read where tapping on the engine block will cause a noticeable change (in some vehicles) in the engine due to the knock sensor varying the timing.

The symbol on the diagram does seem to be a piezoelectric device. As for the wiring it appears the wire is shielded. This is common on devices that have very small voltage or current, and prevents induced signals from affecting the circuit. Also notice on the diagram there is a jumper passing through the intermediate connector and at the ECM end a wire from both knock sensors are tied together into the ECM and then on to a ground. This is the shield being grounded on the ECM end, and I believe this is why it's marked (s). Shields are always grounded on only one end to prevent ground loops (more induced signals). Having said all that here is what you have:
1. One wire running from the Sensor to the ECM
2. The sensor is grounded through its own case to the block.
3. Under the cover of the wire is the shield. A conductive mesh or foil (like on a TV coax). This shield isn't and should never make connection with the main wire inside. The shield is connected to ground on one end only with the other end open. The shield needs to be a complete circuit all the way from the knock sensor to the ECM where it is then grounded. This is why the diagram shows a jumper going around through the intermediate connector to complete the circuit for the shield. Showing it the way they do is misleading and makes you think its part of the knock sensor wire.

To check the circuit out you need to make sure the knock sensor wire has continuity from the sensor to the ECM. Then you need to connect your ohmmeter to the shield at the sensor and make sure it's grounded. Then read from the knock sensor wire to the shield and make sure you don't read continuity.

I worked on Jet A/C wiring for over 38 years and found many times that a shielded wire chaffed through and came in contact with the shield. This of course would ground the circuit at that point. One way you could make sure the wire isn't grounded to the shield would be read to ground. This is the test mentioned in the manual where you connect the meter to the sensor connector and ground. If you read continuity to ground it might to be coming from the shield.

I believe I'm right, but motorcycle wiring diagrams really suck compared to aircraft w/d and I am making some assumptions.
Click to expand...

People and information like this is why these forums are so valuable. I don't know what we would do without this, the dealer certainly would not know these things.
 
Well I continue to toil away on this problem..I think I have it resolved and 300-400 miles later it returns.

I have been completely through the circuit, replace wires, connectors, terminals, cleaned and used di-electric grease on 95% of the connections on the entire bike.

I am just about at the point of running a separate new circuit from the Knock sensor back to the ecm to isolate it out from everything else.

I have made on observation that i don't have a correlation for yet.

When I get the FI light(25 error-left knock sensor) and I turn off ignition via the key, it will usually come back quickly when rpms stay above the 4000 range for the 10 plus seconds, However, if I kill the engine via the kill switch only and restart, I can go XXX miles before light comes on again...as high as 250-300 miles. Not sure why this is so yet. might be a lead there somewhere.

Anyway, the battle continues...:mad:
 
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