100 series Rear Diff lock Light. Help needed!
- Thread starter Akshay
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Center Diff locked?
- Thread starter
- #3
The Center Diff lock works. Though I dont think this is operated by the same ECU as the rear diff lock. If I'm not mistaken.
A few points to note:
The center diff must be engaged and the transfer case must be in L before the rear diff motor will run and try to engage the rear diff lock.
The center diff does not have a ‘smart’ ECU, it’s just relays and switches. Thus, the dash indicator does not illuminate on start up.
The rear diff has a ‘smart’ ECU (monitors transfer case position and center diff) so you see its dash indicator illuminate briefly on start up, and flash when the rear diff switch is ‘on’ but either the center diff is not engaged, or the transfer case is not in L, or the diff lock hasn’t physically engaged yet.
The rear diff light will stay on only when the center diff is engaged, the transfer case is in L, and the rear diff lock is physically engaged by the motor and actuates the sensor switch. Phew.
If the rear diff dash indicator does not flash when the switch is turned to ‘on’ then there is a problem with the switch or ECU.
The center diff must be engaged and the transfer case must be in L before the rear diff motor will run and try to engage the rear diff lock.
The center diff does not have a ‘smart’ ECU, it’s just relays and switches. Thus, the dash indicator does not illuminate on start up.
The rear diff has a ‘smart’ ECU (monitors transfer case position and center diff) so you see its dash indicator illuminate briefly on start up, and flash when the rear diff switch is ‘on’ but either the center diff is not engaged, or the transfer case is not in L, or the diff lock hasn’t physically engaged yet.
The rear diff light will stay on only when the center diff is engaged, the transfer case is in L, and the rear diff lock is physically engaged by the motor and actuates the sensor switch. Phew.
If the rear diff dash indicator does not flash when the switch is turned to ‘on’ then there is a problem with the switch or ECU.
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- Thread starter
- #5
Thank you
My main concern was why the light doesn't blink when switch turned on. I did know that it needs to be in L for it to activate but was wondering why I'm not getting it to blink. The switch is a simple on off switch. Measured the continuity with a meter.
Will try swap the ECU with a known one.
Could it the switch on the locker itself?
Should blink when it's not engaging.. Either if the actuator isn't working or the transfer isn't in low, etc. Never heard of a failed ECU either.
I'd check for wire issues, for example where the harness goes near the exhaust it tends to melt if the exhaust has a hole on it.
I'd check for wire issues, for example where the harness goes near the exhaust it tends to melt if the exhaust has a hole on it.
Has it ever worked? If they (rear diff) is not exercised regularly, they will seize up. My 06 had that issue,.
But it should blink regardless
Right, if it doesn’t at least blink when the switch is moved to ‘on’ then the issue is with the ECU or in-cab wiring or switch.
The switch on the diff is only to detect when the lock mechanism has fully engaged. Last step in the process, lots has to happen before that switch is involved.
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- Thread starter
- #10
Found the issue. One wire was receiving 0.5v instead of 10-14v. All sorted now
Reviving this older thread. I’m having a similar problem as the OP:
Haven’t had the truck rear-locked for about a year. Took it out today to exercise the lockers.
- Transfer case in L
- Center locker engaged (confirmed) by steady dash light
- Rear locker engaged (switch turned to RR)
The rear locker dash light blinks for about 1/4 mile at ~10mph before turning steady red. Is this typical? I recall it had never immediately turned steady like the center, but this feels extra long. Troubleshooting?
Haven’t had the truck rear-locked for about a year. Took it out today to exercise the lockers.
- Transfer case in L
- Center locker engaged (confirmed) by steady dash light
- Rear locker engaged (switch turned to RR)
The rear locker dash light blinks for about 1/4 mile at ~10mph before turning steady red. Is this typical? I recall it had never immediately turned steady like the center, but this feels extra long. Troubleshooting?
…it’s also slow to unlock. After driving for a minute with both diffs locked (confirmed by steady dash light), I stop, shift L>H, center diff switch OFF, rear diff OFF. The center diff turns of immediately but the rear needs a few hundred slow-driving feet before I hear a loud click and it disengages.
Normal. If you're driving in a straight line, it can take a minute.