For the VGRS you need to also turn the wheel lock-to-lock as well as go straight at 25MPH. Hopefully it's that simple.
5-speed A750 trans won't shift in to 5th gear.
- Thread starter MongooseGA
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- Thread starter
- #262
The lock to lock is new to me, I don't know that I've ever done that before. I'll give it a shot.
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- #263
Confirming 25mph and then lock to lock is what ultimately cleared it for me. I don't think I've ever done this before. I usually just pull out of my driveway, go down to the nearest culdesac and get to 25mph on the 1/8 mile back to my house 
So I got TechStream on my laptop. Took it outside and pulled the following codes:
I tried clearing the top 2 codes (both in ABS/VSC/TRAC system) and neither seemed to clear. They never left the screen. My ABS light did go off, but it has been intermittent. Exiting TS and then retesting gave the same codes. Am I now looking in to the wiring harness (again) or the ABS/Skid control ECU?
Also confirming, clearing the L4 pickup code (which is the 1268) did not seem to change anything in driving. Still locked out of 5th. My new sensor/switch arrives tomorrow. I will install it, put my rear shaft back on, and see if anything changes.
Continuing to google...
I believe the airbag code is related to the VSC being off due to the CDL being locked. It's a code related to roll-over sensing. Will retest tomorrow after reinstalling the rear shaft. I'll test through low range as well. The truck already torque steers enough in FWD high range..
So I got TechStream on my laptop. Took it outside and pulled the following codes:
I tried clearing the top 2 codes (both in ABS/VSC/TRAC system) and neither seemed to clear. They never left the screen. My ABS light did go off, but it has been intermittent. Exiting TS and then retesting gave the same codes. Am I now looking in to the wiring harness (again) or the ABS/Skid control ECU?
Also confirming, clearing the L4 pickup code (which is the 1268) did not seem to change anything in driving. Still locked out of 5th. My new sensor/switch arrives tomorrow. I will install it, put my rear shaft back on, and see if anything changes.
Continuing to google...
I believe the airbag code is related to the VSC being off due to the CDL being locked. It's a code related to roll-over sensing. Will retest tomorrow after reinstalling the rear shaft. I'll test through low range as well. The truck already torque steers enough in FWD high range..
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- Thread starter
- #264
Thinking on this a little more. Does VSC being off (or CDL being locked) negate 5th gear for any reason? I don't believe I've ever tried locking the CDL on pavement beyond just testing function at low speed, so I can't say I've ever had it locked while the truck would be in 5th gear.
Can test this thought tomorrow.
Can test this thought tomorrow.
What does the freeze frame data look like on that ABS code? Should be able to pull it up by clicking that blue cloud.
Not at home at the moment, so I can't dig through the diagnostic manual to look at the ABS code.
I can say that locking the center diff doesn't lock out 5th.
Not at home at the moment, so I can't dig through the diagnostic manual to look at the ABS code.
I can say that locking the center diff doesn't lock out 5th.
I'm still driving around (when I drive the truck...) in RWD only after grenading my front diff at COTR, lol.
- Thread starter
- #269
Just posting for posterity.
Searching the existing codes, there's a mention or two about weak batteries. Before putting the new ECM in, I had the battery disconnected and on charge for a few days. It's only 3-4 years old but has been weak since at the trans shop.
It started getting cold in the mornings when the 5th gear thing came back up recently. It was weak and needed a jump tonight.
Just to rule out something stupid, I put it on a charger again tonight.
Additionally, this whole issue started after a weekend trip through torrential rain. Like, actual hurricane Helene rain. The brake code seems to be common in circumstances of water intrusion. The brake code did not present itself when I hooked up TS to it the other day. It has since rained for several days. The code is now present.
Maybe that's coincidental.
Searching the existing codes, there's a mention or two about weak batteries. Before putting the new ECM in, I had the battery disconnected and on charge for a few days. It's only 3-4 years old but has been weak since at the trans shop.
It started getting cold in the mornings when the 5th gear thing came back up recently. It was weak and needed a jump tonight.
Just to rule out something stupid, I put it on a charger again tonight.
Additionally, this whole issue started after a weekend trip through torrential rain. Like, actual hurricane Helene rain. The brake code seems to be common in circumstances of water intrusion. The brake code did not present itself when I hooked up TS to it the other day. It has since rained for several days. The code is now present.
Maybe that's coincidental.
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Hmmmm, interesting. Might be worth checking the connections at the ABS control unit attached to the brake booster.
The ABS/Skid control computer is right above the driver side fuse box in the footwell, right? Right where you might get water intrusion with a bad windshield seal?
The ABS/Skid control computer is right above the driver side fuse box in the footwell, right? Right where you might get water intrusion with a bad windshield seal?
- Thread starter
- #271
It's a little further in. It's immediately left of the brake pedal. I would expect that if water was making to this module I'd have been seeing plenty of it on the floor as well. What's odd is that it had given a specific code for the right rear ABS sensor while it was at the shop, but not now.
I can definitely test/ check connections.
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Gotcha. I'm not sure where the junction blocks for that computer live - I seem to remember looking at the diagram that the wiring to (at least) the T-case position sensor hit a junction block before going through the firewall.
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- #273
I'll try to look today. I'll pull the unit, clean the connections on it and under the dash, and behind the booster. I'll also cycle through low range a few times and see if that jars anything.
I believe if you're in low range it won't let it go into 5th gear. Not sure if the CDL does the same thing in high range.
maybe whatever sensor controls that is stuck on thinking you're in low?
- Thread starter
- #275
That's the current theory. It would be the L4 pickup switch located on the case which I posted a picture of the other day. I pulled mine, it tested bad. I cleaned it with connector cleaner and 2x 9v batteries (as described in the link I posted) and it tested well. Put back in the truck and no change. So either the switch really isn't actually good now, or there exists an issue further up the stream. Either wiring or the module, possibly. I have a new OEM switch being delivered today so I can rule that out.
Interestingly, the neutral sensing switch on the case (located immediately to the left of the L4 switch) also tested bad. I cleaned it, did not retest it, but still no dice. So I have at least one switch that should be good, but both of them act as bad (it seems). They would both join in to the same harness which ultimately hits a connector on the very top of the trans bellhousing, visible from above behind the engine.
For high range, the CDL does not lock out 5th gear. LJE reminded me of this last night. I've driven my truck in 2wd numerous times and never had the issue while the CDL was engaged.
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- #276
Am I understanding this correctly that the truck is saying the trans is in park and case is in neutral?
If that's the case, that's probably something. Trans was in park but case was in high. Moving the case lever to low and rechecking did not change it.
I did also clear the airbag code and it went away. The other 2 mentioned yesterday are still present and cannot be cleared.
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- #277
I don't know what I did, but I was able to clear ABS/L4 the codes finally. They went away from the screen in TS. "Brilliant!", I thought. Until I put my foot on the brake to put the truck in gear to drive, and the codes both popped back up immediately. I have not been able to clear them again.
Airbag code did go away. I didn't recheck it though, not as concerned with him.
Airbag code did go away. I didn't recheck it though, not as concerned with him.
Hmmmm, I'm actually not sure. When you pull up the transmission page, how do those values change as you cycle the transmission & the T-case lever?
That doesn't shock me - best we can tell, your transfer case has zero idea what position it's in, hahaha.
Definitely getting more suspicious of water intrusion issues though.
