What causes the diff lock light and the 4LO light on the dash flashing? (1 Viewer)

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Occasionally when I start the vehicle in the morning the yellow diff-lock and 4LO light on the dash are flashing.

When it does this you cannot switch into 4LO.

Sometimes I turn the vehicle off and then back on and then it goes away; and sometimes that does not work.
Then if I drive about 1/2 mile and then turn the vehicle off and back on it goes away. That seems to work everytime.

What causes this and how is it corrected?

Seems more frequent on cold mornings. This happens every few months.
 

TeCKis300

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There's probably several slightly different reasons, but I'd chalk it up primarily to electro-mechanical wear and corrosion within the CDL or 4LO actuators.

Almost a year with the fix I did below and it has not reared its head since. With switching confidence and performance improving 100% when off-road.

 
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There's probably several slightly different reasons, but I'd chalk it up primarily to electro-mechanical wear and corrosion within the CDL or 4LO actuators.

Almost a year with the fix I did below and it has not reared its head since. With switching confidence and performance improving 100% when off-road.



Nice write up !

Thanks !!
 

Markuson

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Occasionally when I start the vehicle in the morning the yellow diff-lock and 4LO light on the dash are flashing.

When it does this you cannot switch into 4LO.

Sometimes I turn the vehicle off and then back on and then it goes away; and sometimes that does not work.
Then if I drive about 1/2 mile and then turn the vehicle off and back on it goes away. That seems to work everytime.

What causes this and how is it corrected?

Seems more frequent on cold mornings. This happens every few months.

Could be unrelated Evap error codes. When they trigger, it annoyingly keeps us out of 4Lo, etc.
OBD2 reader to check.
If evap related...Reset codes.
All better......til it does it again. ;)
 
Last edited:
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Thanks .. I'll check for codes next time. In the intern I'll lock the diff when I go 4LO so the diff lock also get used more frequently.
 
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Sounds like the sticky CDL actuator that a lot of us have experienced. A fluid change plus regular exercise helped mine.

Which fluid did you change? My LC diff lock light has been acting up in colder days (happened 3 times so far in last month). Something that hasn't come up for a year. Scared to address the issue. It comes for a few days and disappears for long time.

SQOD: Does it hurt LC driving with that light on?
 

afgman786

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Which fluid did you change? My LC diff lock light has been acting up in colder days (happened 3 times so far in last month). Something that hasn't come up for a year. Scared to address the issue. It comes for a few days and disappears for long time.

SQOD: Does it hurt LC driving with that light on?
Are you talking if the CDL light is flashing? That won't be a problem as it usually means its not engaged if its on first start. It might be annoying and you can drive 10mins or so to make sure everything is warmed up, then cycle the engine off/on again to get the light to go away. I've got issues and just drive with the flashing like cause why waste a start on the starter to turn that light off.
 
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Yes, I think in 100 it was call central diff lock, which Im not sure when you are supposed to turn that off? I have wasted starts and it doesn't go away even after driving 10 mins. It does go away after 5-6 hours.
 

ga12r1

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Could be unrelated Evap error codes. When they trigger, it annoyingly keeps us out of 4Lo, etc.
OBD2 reader to check.
If evap related...Reset codes.
All better......til it does it again. ;)
I was battling "purge valves stuck open/closed" codes for a few months causing the lights about every 5th start. I finally pulled the canister and sprayed liberal amounts of MAF cleaner through all the tubes. Its been 3 weeks and no lights. 😎

If the lights go after restarting the truck once its warm its probably not evap related though.
 
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I had this happen but my car threw a code, 2447, air pump valve stuck. Hopefully not your issue. The 5.7 has issues with this sort of thing and is all over the tundra boards. Good luck, hope it’s nothing major.
 
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Which fluid did you change? My LC diff lock light has been acting up in colder days (happened 3 times so far in last month). Something that hasn't come up for a year. Scared to address the issue. It comes for a few days and disappears for long time.

SQOD: Does it hurt LC driving with that light on?
Transfer case fluid change may help if the issue is a sticky actuator. If you don't want to spend the $80/liter for the 75W LF stuff that only Toyota makes, you can use Ravenol 75W available from Amazon for like $20. That's what I use. That said, whether I've had Toyota 75W LF, Amsoil 75W-90, or Ravenol 75W in it I still occasionally get the flashing CDL.

In general when this happens if you drive for a bit and warm up the drivetrain and engine for 5-10 minutes, then turn the truck off and restart it, the light goes away. I think there's either some sort of self-test or more likely some sensor which misreads (e.g. looking for a resistance value of 100-1000 ohms or a specific voltage) at start time at which puts the CDL goes into "duhhhhh" mode when it is outside the expected range. Once it warms up everything reads fine and it'll clear on restart, The actual fix for this is probably what @TeCKis300 did and that's to take apart the actuator motor and clean it. Most likely the contacts in the motor are dirty and so the resistance is too high and so the CDL goes into stupid mode to prevent damage which might be caused if it was repeatedly trying to activate but can't. (just my theory).

It doesn't hurt you to drive with the light flashing. That said while it's flashing you can't engage the CDL nor can you engage 4Lo.
 

1world1love

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It's interesting. The only mark on the service records when I bought my truck was the flashing diff lock problem. The notes chalked it up to user error.

About a week after I bought it, I had the diff lock flashing light issue. It went away the next time I drove it.

A few months after that, I got the 4lo flashing and not engaging. It went away after the next restart.

Its now been two years and I have never had either one happen again, knock on wood. I engage 4lo pretty regularly (relative to total drive time), but I almost never engage central diff lock.
 

Markuson

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It's interesting. The only mark on the service records when I bought my truck was the flashing diff lock problem. The notes chalked it up to user error.

About a week after I bought it, I had the diff lock flashing light issue. It went away the next time I drove it.

A few months after that, I got the 4lo flashing and not engaging. It went away after the next restart.

Its now been two years and I have never had either one happen again, knock on wood. I engage 4lo pretty regularly (relative to total drive time), but I almost never engage central diff lock.

Wgats annoying is...a wide array of various sensor errors can lead to a flashi g diff, 4Lo, etc...or basically keeping you from engaging it til cleared.
 
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Which fluid did you change? My LC diff lock light has been acting up in colder days (happened 3 times so far in last month). Something that hasn't come up for a year. Scared to address the issue. It comes for a few days and disappears for long time.

SQOD: Does it hurt LC driving with that light on?

Sorry for the slow response - I changed the transfer case fluid. Before fluid change I would get the flashing CDL light when it was cold in the mornings. I changed all sorts of fluids, but used the Ravenol stuff mentioned for the transfer case. If I slack off about working the CDL actuator a couple times a month then I may see the flashing CDL light, but if I let it warm up and restart then it goes away.

Change fluid and exercise the actuators about every week or two and you should be good to go.
 

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