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Old 01-16-2020, 10:19 AM
kc10mec kc10mec is offline
Join Date: Feb 2012
Posts: 4
Default 2003 limp mode with codes/HELP CAN'T FIGURE IT OUT

Good afternoon,

I've been fighting with my 2003 LB7 since I got rear-ended back in September. It sat for almost 3 months getting fixed, and now Alli is throwing a P0700/P0747/P0880 and C0055 in that order on EFI live.
I have changed the fluid and filters,
Pulled A-trim solenoid cleaned/checked ohms at 5.5,
Changed internal wire harness (because I had it)
Change speed sensor/check wiring (61ohms in circuit)
NSBU and ignition switch changed
Shot the TCM c1-1 to c1-5 it's good there, shot the wiring from ignition switch to fuse box in cab, 12 volts, then from there to under hood box, 12 volts, from there to TCM 12 volts. Every pink wire has 12 volts around there. I'm at a loss here and about to military move to Missouri from Florida on the 29th. Thank you for any ideas or help provided!!!

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Old 01-16-2020, 10:55 AM
Mike L.'s Avatar
Mike L. Mike L. is offline
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Location: Disneyland, CA
Posts: 15,074

Check wheel speed sensors.
Inglewood Transmission Service
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Old 01-16-2020, 04:25 PM
kc10mec kc10mec is offline
Join Date: Feb 2012
Posts: 4

I just got done pulling both sides apart, checked hubs they are tight, wheel speed sensors got cleaned, ohmed the same both sides and got about 1 Vac when spinning by hand...not that that is a perfectly acceptable check. Is there a way to check them on EFI live that I haven't done?

I can change both speed sensors out but they won't be in until tomorrow. I double checked and cleaned every ground I can get my hands on (both sides of motor and under driver's door) going to recheck voltage to the TCM now. Anything else you can think of Mike? Thank you for your help!
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Old 01-16-2020, 04:27 PM
kc10mec kc10mec is offline
Join Date: Feb 2012
Posts: 4

Shot all wires again at TCM and finally got it back together enought to drive... Cleared codes out with EFI live, started up, and instantly got C0055 code only. Drove for 5 min got the same codes as previously mentioned. If I slam on the brakes the trans goes to neutral then hard shift to first. If I ride the brakes like a normal stop it will downshift all gears then 2-1 hard shift and shift range inhibited.

Forgot to mention there is a delay when shifting to drive (fast or slow) even after letting it sit running for 10 minutes or more. Maybe all this info will help with troubleshooting.

Last edited by kc10mec; 01-16-2020 at 06:54 PM.
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Old 01-16-2020, 10:28 PM
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dndj dndj is offline
Join Date: Apr 2019
Location: Oregon
Posts: 108


C0055 is an ABS code for the Vehicle Speed Sensor, in the tailshaft of the transfer case I think, assuming you're 4WD. Code sets when
  • EBCM detects open or short on the speed sensor circuit for 0.5 sec
  • EBCM detects absence of signal for 5 sec
  • EBCM detects erratic signal for 0.2 sec

I'm guessing that's going to create all kinds of havok for the trans. Since you said you replaced already, must be intermittent short or open somewhere?
2003 (LB7) 3500 dually EC/LB->FB, Allison by [email protected], PPEI, AD100, Banks Intake+4" exhaust,CTS2
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Old 01-17-2020, 01:14 PM
kc10mec kc10mec is offline
Join Date: Feb 2012
Posts: 4

dndj, you're right it is pointing to the tail shaft VSS, I think I'm at a point now to try and figure out how to read all of the speed sensors on EFI live (which I haven't had the chance to look at yet) and see if it's reading anything in comparison to the other ones. I traced the wires and couldn't find a break but that doesn't mean much at this point. Continuity checked good but again draw could be a factor. I'm no electrician by any means but I'm trying. If anyone has a good idea where or how I could check that wire run better I'm open!

Wheel speed sensors aren't in yet either but I'll have them just in case.
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