P0638 Fault Code

[NTXFJR]

P0638 code says that the bank 1 throttle actuator is in the wrong indicated position, wiring issues, or controller issue. However, the symptoms I'm seeing don't completely line up with this imo.

My feej sat for most of the past year under a cover patiently waiting for my new garage to be built. Couple that with working 7 day work weeks for much of 2023 which left virtually zero time to ride. It had a vary hard time starting in December, at first running on 2 or 3 cylinders which eventually mostly cleared up but it still ran a bit ragged. Dump some injector cleaner down into the nearly empty tank, and add a couple gallons of fresh gas in hopes that things would clear out. It now has somewhat better but still hard-ish starts after sitting overnight and the mil light is now coming on, but it usually clears up after a minute or 2. I've reset the mil 2 or 3 times now and it will stay off as long as I ride the bike around a bit, but it will come back after sitting overnight. I rode it to work the other day, 42-ish miles round trip, and by the time I got home it sounded like it was running on 3 cylinders. Cleared the fault again this morning and fired it up and the misfires cleared up after a minute or two.

This particular fault code defines an improper throttle signal level to the controller, but my hunch about the fuel injector symptoms doesn't seem to jive with that. Thoughts?

[raYzerman]

Does the display show the fault while running (on the dash panel)...... if not, then it may not be an Active fault. If stored, it's only history.
Check Engine Light should go out on its own at some point, provided there is no active fault. If it's coming back intermittently, then possibly a flaky connection causing intermittent active fault??
It should have nothing to do with fuel or the injectors, it's electrical....... so, how about unplugging the TB servo motor to refresh that connection. ECU is harder to get at maybe but I doubt there's a bad connection there. Servo motor is wired direct to the ECU, no connectors in between, only a connector at the servo motor and ECU.
Can't help you with where the servo motor connector is on the TB's.... FSM says you'll have to remove the airbox........ likely underneath at the rear of TB's is my guess.
Worst case, the diagnostic indicates a bad servo motor..... I'd want to check some more before coming to that conclusion....... You are in luck, the FSM describes a test!!
Check Owner Manual for "Electronic Throttle Valve" fuse..... identified as fuse #18 on the wiring diagram.... might be corroded?? FYI, Yammy mislabeled the wiring diagrams... ES is A, and A is ES.

[NTXFJR]

Thanks for that awesome and informative post Ray.
Makes sense that the misfiring issues are probably not directly related to the controller's issue with the throttle body.
After posting and then thinking about it a bit, I decided to get a fuel injector service kit coming along with some aerosol injector cleaner for what I suspect is stuck/clogged injector(s). I will plan to pull the injectors and service them one by one off of the bike.
For the fault code, I like that tb test procedure you show using the C batteries. I have some tb cleaner coming, and also contact cleaner and anti corrosion compound to service the harness connections.
Will report back with the findings.

[raYzerman]

Festus to the courtesy phone..... when cleaning injectors, I believe you can cycle the injectors open with a 9V battery?? Would clean better if open, and just me, but I'd not leave them powered up too too long (30 seconds??).
IF I were cleaning injectors, I'd just send them to somebody for a flow report before and after, and that will tell you if you really had an injector problem.

Also forgotted to mention, on pre-OBD Gen3 FJR's you could manually go into diagnostics and reset the ISC (Idle speed control) if need be. I don't have me an OBD equipped FJR here, so don't know if the cheap readers even have that in the menu.......... however, try all your other shit first and hopefully you have good results. I'm still not seeing how an injector problem causes a communication error between the servo and the ECU.........

[Festus]

Send them to me, I'll clean them and post the results. I have the machine. No charge, other than paying the return shipping.

[FJRPittsburgh]

Send them to me, I'll clean them and post the results. I have the machine. No charge, other than paying the return shipping.

A man of many talents......

[NTXFJR]

Festus to the courtesy phone..... when cleaning injectors, I believe you can cycle the injectors open with a 9V battery?? Would clean better if open, and just me, but I'd not leave them powered up too too long (30 seconds??).
IF I were cleaning injectors, I'd just send them to somebody for a flow report before and after, and that will tell you if you really had an injector problem.

Also forgotted to mention, on pre-OBD Gen3 FJR's you could manually go into diagnostics and reset the ISC (Idle speed control) if need be. I don't have me an OBD equipped FJR here, so don't know if the cheap readers even have that in the menu.......... however, try all your other shit first and hopefully you have good results. I'm still not seeing how an injector problem causes a communication error between the servo and the ECU.........

I totally agree. I’m betting that they are completely separate issues with the only thing in common being that the bike sat for so long causing it to get crusted up. I hate ethanol laced fuel btw.

[NTXFJR]

Send them to me, I'll clean them and post the results. I have the machine. No charge, other than paying the return shipping.

Thanks for that generous offer Festus. I may take you up on that if my action plans go south.

[Cav47]

Craig,

Sorry you are having some mechanical issues, but it is good to see you back on the board. Don't be a stranger.

[NTXFJR]

I finally got around to getting my feej put back together this past weekend. It originally popped up with a P0638 code which has to do with the throttle body actuator position, and it would hard start and run, but it was also stumbling with occasional misfires.

The symptoms didn't really add up in my mind for them to all be coupled with the throttle body feedback signals, so I opted to take a 2 pronged approach, first clean all harness connectors, then check the fuel delivery components since the bike sat in storage for so long last year with untreated fuel in the tank.

I gave the harness connectors a cleaning with CRC QD contact cleaner, then applied some Noalox anti oxidant compound to them before reassembly.

For the fuel system, I pulled the fuel pump out of the tank and found that the strainer screen had a shellac coating all over it. There are some crustys laying under it from scraping on it a bit. I figure this came from dumping injector cleaner treatment into stagnant untreated fuel. Lesson learned, don't put off treating the fuel when storing long term. I borrowed a strainer screen from the pump on a spare tank I have which was definitely cleaner.



Next came pulling the throttle body assy off and going through it with throttle body cleaner, and flushing the fuel supply hose connecting the throttle body assy to the fuel pump.



Next would be the injectors. I bought one of those diy injector cleaner kits off of Amazon, I opted to go this route instead of sending them in for a professional cleaning because when I pulled them they didn't look that bad. That assumption was verified when the cleaning procedure gave a good spray pattern on all 4 injectors.



With that done, I put the bike back together and tried starting it. It had a hard start still with the occasional misfires still there. The P0638 fault light went away but now there is a PO118 fault light showing? Turns out it was a temperature sensor malfunction. Ok, I must've missed that connection when going back together, smh. That's where the bike sat for a few weeks until I could get back to it again. I pretty much figured the cause for the temperature fault, but the stumbling misfires had me scratching my head for a bit. In the end, I opted to replace the fuel pump due to it being so crusty, the new screen didn't seem to help, and there were no other obvious issues.

This past weekend, I installed the new fuel pump, found the missed loose temperature connection, and crossed my fingers on start up. Thankfully that cleared up the misfiring issue. Amazon $228, 2 weeks from China



Next step was doing a long overdue throttle body sync. Carbtune might not be the most sensitive gauges out there, but they are easy to store and they definitely got it closer than where it was.

In the final analysis, it appears that at least in this case, cleaning the harness connectors and cycling the tb's a few times took care of the PO238 code.

[FJRPittsburgh]

Wow! That's a rewarding ending to this story. Congrats!

[Hppants]

Well done, Craig.

Ride more, stress less, my friend....

[FJRoss]

Nice!
Did you clean or replace the inlet strainer baskets on your fuel injectors? Did you replace the grommets/gaskets?

I saw a variety of fuel injector cleaner/tester units - any reason for choosing that one? If they work, the price is far less than getting someone to do it for you. Probably wouldn't hurt to have an ultrasonic tank as well, although I would only immerse the injector tips.
Edit: Did you rig a pressurized fuel source to evaluate flow rate and spray pattern or is that outside of what can be accomplished with that device?

[NTXFJR]

I didn't replace the strainer baskets as they didn't look that bad. I chose the service kit based on features it had and price. I used the aerosol pressure from carburetor cleaner spray to pressurize the injector while cycling power to it. I judged the spray patterns by comparing them to each other. Not overly precise but I figured it would be good enough since they weren't that bad to start with. The fuel pump strainer screen seemed to have done its job and saved the rest of the fuel system.