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Transmission cold limp mode.


vf24renegade
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Hi All, 95 WD21

I have a transmission issue on which I cannot find a like submission. When it's cool or cold (below 60 degrees), especially in the morning, the transmission acts like it's in limp mode. But, after I drive it a bit (100 yards or so), and turn off the key then restart, it shifts normally. The transmission light flashes about 16 times all the same rate, none longer than the other. The manual specifies 10, but all the same length reads no trouble codes. When the weather is warm or the engine is warm, no problems. If it were extreme cold, I might suspect thickening fluid and a partially clogged cooler but not at 50 degrees certainly. I had previously changed the radiator from a 94 pathfinder which had no transmission issues. At some point, I'll add a transmission cooler but for general principal, not for this reason. It may help in this case, but I was wondering if anyone had any thoughts or experiences. Once restarted, the transmission shifts up and down well without any issues.

Thanks

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Hi, sounds like everything is functioning normal. Auto trans will only engage overdrive once the trans fluid temp sensor reaches 80 Celsius. Usually this can take anywhere from 3 - 5 mins depending on weather conditions. I notice if the ambient temp is about 20 Celsius it takes about 3 mins.

So by running the engine and then turning it off, the trans fluid will still be heating up a little more before it starts to cool. Which is why you'll find it starts shifting into overdrive after restarting as the fluid will be already heated.

Trans cooler is a great idea, heat can kill autos and I recommend changing fluid if you notice it's lost the nice pink color, doesn't smell sweet like it should, also feel the actual dipstick with the fluid on it. If the fluid feels gritty and not smooth then definitely change it...quickly.

I change mine every 16,000 miles, some say it's overkill but I have done over 120,000 miles on this current trans, it pulls hard up steep hills with no troubles at all so I must be doing the right thing by keeping the insides clean.

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Huh? Limp mode locks the trans in third gear. That is not normal, no matter how cold.

 

Looking at the manual, is it possible that what it's actually showing is the on/off pattern on AT-41? Looks like a reversed battery, low voltage, or a long time without voltage will make it just blink at you (and it doesn't say how many times it'll do it). The "long time without voltage" is interesting to me. It looks like the TCU has two power feeds running through the fuse box, one switched with the ignition and one not, so the one that's not is probably how the unit remembers if it has a stored code or something. If it's not getting power on this line, it might trigger the "battery has been disconnected for a long time" error when the ignition switched line powers it on again. Then when you shut off/restart, if you're quick about it, there could be a capacitor or something inside the TCU that keeps it alive for the moment that power is disconnected. AT-37 shows the location of the fuses in the box (you could check for power at the plug for the TCU as well).

This is a shot in the dark, of course, I have no idea if that fault is enough to trigger limp mode.

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I have the exact same problem - locked in third gear (or second if you manually put it into "1st") until it warms up and is restarted. In my case, it happens when it's below 40ish. There's been a few times where it's been cold (single digits) where it started and drove fine without warming up.
I ran the diagnostic process and got codes 1 and 2: speed sensor and revolution sensor, according to the manual.

OP, does your speedo jump when you start the car? It's something that I've noticed mine will do when cold. The speedo will also jump when I press the brake pedal or turn the lights on. This could be unrelated but my guess is that it's a wiring issue with the speed sensor.

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  • 3 months later...

I have the exact same problem - locked in third gear (or second if you manually put it into "1st") until it warms up and is restarted. In my case, it happens when it's below 40ish. There's been a few times where it's been cold (single digits) where it started and drove fine without warming up.

I ran the diagnostic process and got codes 1 and 2: speed sensor and revolution sensor, according to the manual.

 

OP, does your speedo jump when you start the car? It's something that I've noticed mine will do when cold. The speedo will also jump when I press the brake pedal or turn the lights on. This could be unrelated but my guess is that it's a wiring issue with the speed sensor.

Nope, it just moves forward as if in lip mode. At the end of the drive way, I shut it off and restart and all is fine. This happens as high as the mid 60's F. outside temperature. Also, as a note, it has always had a high idle RPM @1200 to 1500.

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This happened to mine after a windshield replacement, it would leak and water would get into the harness somewhere. I got it fixed under warranty, but it was the exact same symptoms. Sounds like if it is damp out, it does it until the truck warms/drys. I would check all your connections for corrosion or moisture in them. It was the same speed sensor code it threw as well.

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This happened to mine after a windshield replacement, it would leak and water would get into the harness somewhere. I got it fixed under warranty, but it was the exact same symptoms. Sounds like if it is damp out, it does it until the truck warms/drys. I would check all your connections for corrosion or moisture in them. It was the same speed sensor code it threw as well.

 

Thanks, but I doubt that's it. It doesn't warm up in the 100 yards to the end of the driveway. It also does it whether it's damp or dry. Always when its under@ 70 degrees.

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