4 WHEEL DRIVE PROBLEM

RANCHORELAXO09

MEMBER
1994 TOYOTA 4RUNNER
6 CYL
4WD
AUTOMATIC
120,000 MILES

When cold transmission stays in 4 wheel low for several miles unless warmed up extensively. Changing gears or moving the 4x4 shifter has no effect but everything works fine once engine warmed, so far it does not slip back in 4wheel at high 2 wheel drive speeds but told it could? Have had all the electric servos replaced no change, have also changed the triangle shaped shift linkage position indicator on drivers side of transmission, so far no one (Toyota or otherwise) knows what to do! Can we disconnect 4x4 just to drive it? If so how? We have a wiring diagram that says a.D.D system but have no idea what this is? Any advise or ideas greatly appreciated! Will gladly double donation if anyone can help thanks

5 Replies

KHLOW2008

MECHANIC
41,814 POSTS

Hi ranchorelaxo09,

Problem seems temperature related, was the transfer fluid Temperature Sensor checked or tested?

Was the Engine and Electronic Controlled Transmission ECU tested?

Do you have any driveability problems during this period of driving?

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Sunday, March 29th, 2009 AT 8:58 AM

RANCHORELAXO09

MEMBER
3 POSTS

Yes, we checked the temp. Sensor and the ecu and both were fine and the truck does run when in 4 low but obviously only at very low speeds, and it does great once in normal gear, it's the starting up that is the problem. Any more ideas or is there a way to temporarily just disconnect 4 wheel drive so we can drive vehicle safely? Also do you know what the "a.D.D." on the wiring sheet means? We are very determined to figure this out- engine has been rebuilt completely besides whatever this is. Thanks.

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Tuesday, March 31st, 2009 AT 9:36 PM

KHLOW2008

MECHANIC
41,814 POSTS

Hi, Sorry for the delay in replying. Your question got me stumped so I had to spend some time doing research on the problem and possible causes.

I have the explanation for the ADD here.

ADD DESCRIPTION & OPERATION
The Automatic Disconnect Differential (ADD) allows engagement of front differential from 2WD to 4WD while vehicle is moving. On vehicles with ADD, a flange is mounted on the front hub which is splined onto axle shaft connected to side gear shaft on front differential. Locking hubs are not used with the ADD.

When transfer case is shifted into 4WD, the ADD is shifted into 4WD by operation of ADD solenoids which control vacuum supply to the ADD actuator. The ADD actuator engages clutch sleeve with intermediate shaft in front differential and side gear shaft, providing 4WD operation. When vehicle is in 4WD, the 4WD indicator light on instrument panel will be illuminated.

NOTE: ADD solenoids may also be referred to as ADD Vacuum Switching Valve (VSV).

Operation of transfer position switch and transfer pressure switch completes ground circuit which allows ADD relay to operate. When ADD relay operates, voltage is supplied to the ADD solenoids. The ADD solenoids operate and control vacuum supply to ADD actuator for 4WD operation.

Based on the schematic diagrams, one of the possible cause would be a faulty VSV4 ADD solenoid that is leaking vacumn or the solenoid is stuck in open position. Another possibility would be a faulty transfer pressure switch.

To test which is causing the problem, disconnect the VSV4 solenoid wire connector. If problem persists, it rules out the pressure switch. Disconnect and plug vacumn hose of VSV4 and retest. This should disable the 4WD functions as the ADD would not work.

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Thursday, April 2nd, 2009 AT 8:21 AM

21STRONG

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1 POST

Not sure if this problem was fixed, I have the same issue, but the front diff is not engaged when the car is acting up. Any other ideas?

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Monday, May 14th, 2012 AT 4:15 PM

KEN L

MASTER CERTIFIED MECHANIC
47,527 POSTS

It looks like the ADD relay will fix the problem. Here is its location (below)

Please let us know if you need anything else to get the problem fixed.

Cheers, Ken

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