Good afternoon, all. 99 4Runner Limited here 3.4L. Canadian vehicle in the states. (A/C units in Celsius...) I'm having a no 4WD situation. Symptoms first and then what I've tried to diagnose the problem.

Symptoms:
1. All the 4WD lights on the dash flash all the time, all 4 green tire lights and the center lock light. When the 4WD button on the shifter is pressed it goes out for a second but comes back on all flashing.
2. The 4WD does not engage with the 4WD shifter button or with the shifter moved into 4HL or 4LL.

What I've done: (all steps beyond 2 were tested in the field by stomping the throttle on my icy driveway and watching the wheels)
1. Replaced the front diff sensor/switch per all the you tube hype to no effect whatsoever.
2. Checked power at the Vac solenoids, Green wire on blue plug/solenoid has power always, Orange plug never has power.
3. Unplugged both the blue and orange connectors to the Vac solenoids and jumped a hot and ground to the orange solenoid from the battery.
3a. This made no result on the 4WD engaging or dash light situation. I did not repeat the process with the blue solenoid for some reason.
4. Removed the vac line from the manifold at the check valve, removed the vac line to the actuator from the orange solenoid and plugged them together.
4.a This made no result on the 4WD engaging or dash light situation.
5. Reinstated the vac line from the actuator as per its original position on the orange solenoid. Removed the vac line to the actuator from the blue solenoid and plugged it into the check valve on the main manifold vac line as in the previous step.
5a. This time with the 4WD shift lever in 4HL it engaged and the lights on the dash quit flashing and were accurate to the actual position of the transfer case situation. When shifting back up into 4H/2H with the 4WD button depressed the center lock light went out as it should have. Pushing the button again took it out of 4WD. This time when pressing the 4WD button I can now hear the whirring of the actuator on the transfer case locking and unlocking. Once the vac hoses were all reinstated to their original position the original problem presented again and the 4WD button had no effect on the transfer case actuator.

My assumption is I may have two issues. The vacuum solenoid packs are bad (test 3) and the ADD relay is either faulty or has no power or some other wiring nightmare. (test 2)
The solenoid pack is easy to get to and if I can find a replacement shouldn't be a big deal. However, I'll be damned if I can locate or identify the ADD relay. I dropped the knee plate exposing the column and there is just a ˟˟˟˟ ton of stuff under there. Anyone got any clues to how many wires and colors this DP/DT relay has on it? I'm assuming 6 to 8 wires for the relay power, the vac coils and the relay shunting coil.

Thanks in advance, Ron B

 

Check out my build thread. It sounds like the contact traces inside the actuator are boogered up. The blinking indicators can occur any time the position switches give a reading that doesn’t match the metrics.

The 4wd computer isn’t very smart. It knows 4LO, 2HI, 4HI(open), & 4HI(locked). So let’s say the shifter is in 2HI and the position switch on the front diff has a dead spot so it reads “LOCKED”. The 4wd ecu is going to throw the blink for error. It is entirely if -> then models. If any reading doesn’t fit those 4 scenarios, blink.

When testing the position switches you have to connect a multi-meter and check the entire range of that switch. If there is a dead spot ANYWHERE it will put the 4wd ecu into blink. Same with the contacts inside the actuator, if it loses signal, blink.

 

A few years ago you walked me through some of this. To test the position switches, the OP will need to remove them from the transfer case in order to depress the plunger(s) while observing the multi-meter.



Andreas

 

i built my own vacuum solenoid bank to fix the inoperable original unit. Didn't fix anything, I took the two on the driver's side out of the transfer case. I put the meter on them and they toned out on the continuity meter but irregularly. cleaned with brake cleaner and rechecked. They did better but not sure if they are causing me the issue yet. I cannot get to the one on the passenger side without some real effort, like dropping the transfer case a little or pulling the carpet back and cutting a hole in the floor. Maybe it is the error i don't know yet. I don't know what the passenger side one monitors. If it is the 4WL then it shouldn't affect the driveline until it goes into 4WL correct? Also, i think i compounded the issue. Just to be sure I didn't have the vacuum line reversed I switched them and tried it out. The motor ran poorly pry due to a vacuum issue and then made a horrible grinding and clunk noise. Now the 4WD doesn't engage at all even by putting the vac line directly to the actuator vac hose like it did before. So that's not good. Getting tired of messing with this.

Anyone have a link to an electrical/vacuum troubleshooting manual I can work this problem down with? 994Runner limited. Thanks!