2003 2wd will only reverse when cold

[md1m]

My vehicle will only go into reverse first thing in the morning. Once I've driven it will not engage reverse. I posted about this issue two years ago, and asked a few "car people" and had a transmission shop look at it. Everyone told me the transmission was about to fail and I needed to get it replaced or rebuilt. Fast forward to today, and I still use the vehicle as my daily driver. It drives and shifts perfectly when going forward. I bought a new transmission filer and was planning on having that replaced.

Could it be something like a solenoid that I could have transmission shop test when they drop the pan? My plan has been to rebuild the transmission when I started having problems with forward gears but since it continues to drive perfectly in forward I keep thinking there could be a fix to my reverse problem other than a rebuild. 

[Jotegir]

When the 4 speeds start losing reverse it usually is a sign of a failing transmission and not a solenoid like people told you a few years ago. It is very common on these for reverse to go and then some time later the rest. The reason it works when the oil is cold is that there's enough material there to catch the reverse gear and engage on the bits of metal flakes, but not once the fluid has reached temperature and is rather thin. 

 

[Slartibartfast]

I've heard of this with the old WD21 RE4R01A. What happens from what I've read is that one particular snap ring breaks and chews up a sealing surface, which limits your line pressure (because fluid is bypassing internally). Reverse needs the most line pressure, so it's the first to suffer, especially when the fluid is warm and shoots past the damaged seal more easily. Sooner or later the part finishes failing and you lose the other gears. I thought the revised transmission that you've got had this failure mode revised out, but it sure does sound like it's found a way.

 

Before assuming the worst, I would run codes on it, on the off chance the computer has another idea. AT-49 of the '03 manual (download from Nicoclub if you haven't) tells you how to run codes without the Consult scanner. The computer should be able to tell you if there's a wiring fault. Failing that, check the harness for any obvious damage. I wouldn't expect a wiring fault to only act up when cold, but it's worth a look. I would also check the fluid level, warmed up, on flat ground, at idle, though the last trans I saw with low fluid slipped when cold.

AT-356 has specs for line pressure. I assume there's a diagram elsewhere showing where to connect a test gauge to get those numbers. 

If it's shot anyway, can't hurt to drop the pan and have a poke around, though I wouldn't go in expecting a miracle. 

[adamzan]

11 hours ago, Slartibartfast said:

I've heard of this with the old WD21 RE4R01A. What happens from what I've read is that one particular snap ring breaks and chews up a sealing surface, which limits your line pressure (because fluid is bypassing internally). Reverse needs the most line pressure, so it's the first to suffer, especially when the fluid is warm and shoots past the damaged seal more easily. Sooner or later the part finishes failing and you lose the other gears. I thought the revised transmission that you've got had this failure mode revised out, but it sure does sound like it's found a way.

 

Before assuming the worst, I would run codes on it, on the off chance the computer has another idea. AT-49 of the '03 manual (download from Nicoclub if you haven't) tells you how to run codes without the Consult scanner. The computer should be able to tell you if there's a wiring fault. Failing that, check the harness for any obvious damage. I wouldn't expect a wiring fault to only act up when cold, but it's worth a look. I would also check the fluid level, warmed up, on flat ground, at idle, though the last trans I saw with low fluid slipped when cold.

AT-356 has specs for line pressure. I assume there's a diagram elsewhere showing where to connect a test gauge to get those numbers. 

If it's shot anyway, can't hurt to drop the pan and have a poke around, though I wouldn't go in expecting a miracle. 

While it sounds like it is the issue they have, it certainly isn't a common failure point on the 2001+ RE4R01A. There are loads of first gen xterras around with 250K+ on the original transmission.

When my 1995 lost reverse it would work fine in the cold when the fluid was thick. But I believe it is more a varnish issue than broken parts, simply because adding a can of seafoam trans tune would literally "Fix" it for months at a time.

 

OP I would try flushing the fluid out and testing the line pressure. If it's low, you know where to go from there.

[Dbot]

It's only a matter of time before 1st goes out next. I lost reverse intermittently on mine. Fluid flushes and trans coolers couldn't save her. Intermittent reverse issue became more frequent so I swapped it out before it left me stranded 

[md1m]

Just an update to this. My transmission is working just fine. Had 3 transmission shops tell me it was ready to fail and I needed a 3k-4k rebuild. Over 3 years now since I "lost reverse". Still works perfectly in forward gears, and if there's ever a time where it doesn't want to go into reverse, I discovered that I can shift to neutral, then up to reverse and it will catch every time.

 

So heading toward 300k with original engine and transmission working fine

[Slartibartfast]

Nice! Did you do anything to it, or is it just the neutral>reverse trick keeping you going? 

 

If that's all it takes to make it grab reverse, I wonder if the shift cable might just be a little wonky. 

[adamzan]

My old 95 did that too. It seems the momentary bump in N is enough to kick up the line pressure to have it engage... Never lost the forward gears the entire time I owned it. Just learned to live with it the way it was.