No 4th gear: Jeep ZJ 42RE 4.0h (edit) KIA

CajunWon

Well-Known Member
Joined
Aug 5, 2005
Location
Cary, NC
Starting this week. I could use a shop recommendation near Cary.

The transmission has 187k miles. Fluid change within 5k miles (ATF+4) and level is fine now. Tuesday drove 7 hours through mountains and snow, in and out of 4x4 part-time the whole trip. Much of the time 45-50mph in 4th and no issues. Since Wednesday it will not get into 4th gear. 1st, 2nd, 3rd, shifts are normal, obvious and at the right speed. TC lockup occurs at ~35 as normal. I has been cold and there is now much road grime all over.

Where do I start to diagnose this?
There are no DTC trouble codes.
My thoughts: Not the shift-down cable since that would prevent TC Lockup.
Could be output speed sensor. Could be the govenor pressure sensor or govenor solenoid. Could be Overdrive Solenoid. This tranny has never been serviced other than me changing fluid (ATF+4) & filter periodically.
The OD off switch functions normally: maintains no higher than 3rd gear and disables TC Lockup. Overdrive Solenoid. "a 3-4 upshift occurs only when the Overdrive Solenoid is energized by an electrical signal from the powertrain control module." Manual is confusing in that it seems to refer to 4th gear and overdrive as the same gear.
 
Tlc transmission. Lee will probably chime in...
 
Notice also: when the OD switch is On, the TC Lockup will not engage and when the switch is Off the TC Lockup will engage - this is normal operation. However, the shift points are as if the OD switch is always On. And when coasting, the gears drag the engine keeping the rpms up which is only normal with the switch On.

Seems to point to the Overdrive Solenoid is not working, perhaps a check-valve is stuck. The OD switch seems to be working.
 
1994 ZJ
Time to replace Governor sensor and solenoid as preventative maintenance anyway.

Read somewhere a 3-4 shift piston can get stuck. Perhaps worth replacing the whole valve-body $550 which I believe would come with new sensors/solenoid.

Dreaming, but would be nice to swap for AX15. probably harder to find suitable bezel for inside aesthetics.

The key trick flashes 55 on the OD light.
 
TPS tests as normal. .9v - 4.2v and progresses gradually with throttle. Same results as 55k miles ago. Has a solid 5v supply.

Will look at OSS next. Though, with limited relevant experience, not clear how a shaft speed sensor would cause the tranny to default into tow mode (OD Off) and yet allow TC lockup when OD switch is Off.

Edit:the OSS must be within the overdrive unit, overdrive solenoid is within the transmission valve body. Thinking this is now beyond a driveway fix.

My current guess is the overdrive solenoid is malfunctioning, perhaps due to loss of continuity to the OD Switch.
 
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sniff sniff

transmission is completely dead. Jeep at the shop, expecting bad news when they look at it tomorrow.

187k miles with zero repairs, probably not bad for an automatic.
 
The closest place to coast into was Techniquest in Cary. Not like I had a choice as it would intermittently develop forward progress for the last couple miles, and required some pushing to get into a parking spot. I've been an irregular customer there, always good people to deal with and a short jog to the house.

Transmission acted like it was out of oil, but was still full. Couldn't develop enough pressure to engage clutches (imo).
 
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