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4r100 in short bus OSS issues

 
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Old 04-13-2019, 10:31 PM
Josh Cham
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4r100 in short bus OSS issues

Hey, we've converted a 99 2wd e350 short bus into a RV and 4x4 using a 99 f350 4r100, manual transfer case and 05 super duty front axle.

The issue we cannot figure out is the OSS is sending the incorrect speed signal to the PCM and speedometer. This is preventing the transmission from shifting to 2nd gear without locking up the TC and stalling the engine. It is getting proper 2nd shift command (have the Solus plugged in monitoring trans functions.)

The speedometer reads, for example 30 mph when the bus is moving around 5 mph.

We disconnected the TSS and OSS and it will drive and shift with no speedometer reading, however the transmission is flying blind like that on proper shift points and TC lockup.

The trans we pulled out was also a 4r100 and no wiring was damaged during the swap.



Hopefully someone knows if there is a difference in the reluctor for the speed sensors between 2wd and 4wd. That's the only thing left we havent checked!
 
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Old 04-13-2019, 11:53 PM
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Mark Kovalsky may have an answer.
 
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Old 04-14-2019, 05:58 AM
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You may have a bad alternator. They put out EMI when the rectifiers or stator coils go bad that interferes with the OSS signal to the PCM. If you replace your alternator, be sure to add a ground cable directly from the case of the alternator to the negative terminal of the battery. While you are at it, check all your grounds to see that they are in good condition. Bad grounds cause all sorts of weird electrical issues.

Do you have a P0720 code?
 
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Old 04-14-2019, 08:18 AM
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Unhooked the alternator, pin plug and ring terminal to battery and problem still exists.

No codes exist.
 
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Old 04-14-2019, 10:54 AM
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Does the truck have a Vehicle Speed Sensor (VSS) on top of the rear axle? That's where the speedometer signal should be coming from. If it doesn't see a speed signal from that sensor it's going to look at the OSS.

Are you using the original PCM?
 
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Old 04-14-2019, 11:09 AM
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It does Mark, that sensor isnt giving us a speedo reading. We replaced it, and both TSS and OSS. If you unplug the RABS the speedo still reads high, like it's off the OSS.

Original PCM yes. We updated it yesterday trying to remedy this problem, then I came here for help!
 
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Old 04-14-2019, 11:15 AM
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I think (but it's been several many years that the PCM expects a speed signal from the rear diff sensor. There may be a damaged wire to that sensor.

Here's another thought. There is a pin on the PCM that is grounded when the transfer case is in 4x4 low. If that pin is seeing a ground I think it will do exactly what you're seeing. If I had a wiring diagram I could tell you which pin. But I don't have one.
 
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Old 04-14-2019, 11:18 AM
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I will check it out and report back. Thanks
 
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Old 04-14-2019, 11:55 AM
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No damage to RABS harness. Looks good all the way up. Strange because the speedo worked flawlessly before the swap. Which makes me believe its trans related. Not sure how though.
 
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Old 04-14-2019, 04:10 PM
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Did you look at the harness or check it electrically?
 
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Old 04-14-2019, 04:31 PM
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Just did a visual check.
 
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Old 04-14-2019, 05:01 PM
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We have the Solus plugged in and are not getting a reading from the RABS when its moving. Is there a fuse location somewhere for these I'm not seeing?
 
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Old 04-14-2019, 05:30 PM
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The PCM needs an input from the ABS module, not directly from any speed sensor.

Gray/Black wire.
 
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Old 04-14-2019, 05:48 PM
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Originally Posted by Josh Cham View Post
Just did a visual check.
A visual check will find about 1 in 100 problems. The other 99 won't be found by a visual check.
 
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Old 04-14-2019, 06:00 PM
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Correct on the visual check. I was making sure we didnt pull a harness across a sharp edge or smash a wire. Which brings me back to how did something change between a simple transmission swap? Being it drove and shifted fine before. I will pull schematics and test pinouts on the RABS as soon as I find them.
 

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