C-28 FI Error Code - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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  #1  
Old 09-12-2005, 07:27 PM
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Default C-28 FI Error Code

I am getting a C-28 error code on my 2004 DL1000. That is a Secondary Throttle Valve Actuator (STVA) circuit malfunction which can be caused by a loose connection, open circuit or short, STVA motor malfunction, or a ECM malfunction. I have pretty much ruled out a loose connection, open circuit, or short. One of the diagonistic tests for the STVA motor is to measure resistance at the STVA lead wire coupler and it is supposed to be approx. 4.8 to 7.2 ohms. Mine measures 6.2 to 6.4 but since this output appears to be used by the ECM to calculate STV opening, it seems that there should be more of a difference between the fully open and shut positions. It also appears that I only get 1.3 volts from the ECM to the STVA when the key is turned on -- which then goes to zero as soon as the ECU detects an error condition.

In contrast, the voltage sent by the ECM to the Secondary Throttle Sensory Position (STP) (and most of the other sensors) is between 4.5-5.5 volts and the resistance values from the STP that are sent back (depending on STV opening) to the ECM are supposed to be between 1.1 K and 4.3 K ohms.

Do I have a defective STVA if the resistance values are within range but barely change between the open and shut settings?
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  #2  
Old 09-12-2005, 10:26 PM
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Based on the values and the code 28 I would guess it is either the sensor wiring or connector I doubt it is the motor or even the sensor itself, but it could be. And it maybe the linkage from the motor to the secondary butterflies which is causing the fault code. A serious inspection of and reseating of the connectors would be my first step.

A check of the throttle bodies (removal of the air filter) should show the secondaries either in a 1/2 position with the key off or moved to the 1/2 position when the key is turned on. If the latter then the motor and linkage are operating as desired, if the former it would narrow the choices.

Wish I could be more help.
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  #3  
Old 09-13-2005, 01:25 AM
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Quote:
Originally Posted by BradM
Based on the values and the code 28 I would guess it is either the sensor wiring or connector I doubt it is the motor or even the sensor itself, but it could be. And it maybe the linkage from the motor to the secondary butterflies which is causing the fault code. A serious inspection of and reseating of the connectors would be my first step.

A check of the throttle bodies (removal of the air filter) should show the secondaries either in a 1/2 position with the key off or moved to the 1/2 position when the key is turned on. If the latter then the motor and linkage are operating as desired, if the former it would narrow the choices.

Wish I could be more help.
Thanks for the feedback. Every once in a while the error fault goes away and the STVA motor moves the secondaries but most of the time the STVA system is dead. There aren't any sensors for the STVA and there is only one coupler between the ECM and the motor, that coupler is where I took the electrical readings. The coupler only has two wires, one is a power source for the motor and the other gives feedback to the ECM so it can calculate the secondaries' openings.

There is serious lack of information how this system actually works but all the other sensors seem to send voltage signals to the ECM that it uses to make calculations.

Update (9-18-05): My dealer's best mechanic thinks the STVA motor is bad because there is not enough variance in the resistance when the STVs are in different positions. They also think that Suzuki will replace the motor since it is part of the emissions system and are waiting to get approval so they can order a new motor. This may take a while to resolve.

Update (10-24-05): I now have a new STVA motor ($735 part) and everything seems to be fixed. Suzuki replaced the motor since it is part of the emissions control system. They tried to tell me that Suzuki did it out of the goodness of their heart but even the owner's manual states that the emission control system is covered by warranty for 5 years and 30000 KMs (about 18,600 miles).
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