prescott97

Alright, so I know there are a lot of threads about this and I think I've read most of them but am at a dead end so thought I would create a new thread just to see if anyone has any thoughts.

I have a 1997 Limited 4Runner, 6 cyclinder automatic with a 4WD push-button on the transfer case. My 4WD was working when i bought the car in July and stopped engaging about 4 weeks ago (sadly as I was in the Lake Tahoe snow). No 4WD indicator light comes on when the button is clicked, here is what I've diagnosed so far (and from the dealer)

1. Checked both the 2WD and 4WD vacuum switch valves, the 2WD one has vacuum coming out of it and the hose looks fine. 4WD VSV does not have vacuum coming out and does not switch when the 4WD button is pressed.
2. Swapped the hoses so that the 4WD one going to the front diff is on the 2WD VSV, and getting suction. Nothing happens, no light on the dash comes on. From what I can tell hoses look fine.
3. Now, since I was unsure if this was an issue with the 4WD switch or the differential/actuator, I took it to the dealer. The dealer in their first diagnostic could not find the issue (details from that below), and said they needed 2 more hours in which they were gonna charge me upwards of $300 for the labor, but that if I picked up the truck now I wouldn't be charged. So I left the dealership with my tail tucked between my legs but at least no cash taken from me.

Screenshot below of the diagnostic info from the dealer, but it reads. "NO LIGTHS COME UP ON DASH WHEN 4WD BUTTON PRESSED. TRANSFER CASE DOES NOT ENGAGE 4WD. CHECKED 4WD SWITCH FOR CONTINUITY WHEN PRESSED ON. CONTINUITY FOUND IN SWITCH IN ON POSITION. JUMPED WITCH CONNECTOR, 4WD DOES NOT ENGAGE. CHECKED RESISTANCE OF TRANSFER CASE ACTUATOR MOTOR. ACTUATOR MOTOR MEASURES 25 OHMS, WITHIN SPEC. MORE DIAGNOSTIC TIME NEEDED."



Any thoughts on next steps for diagnosing the issue would be incredibly appreciated. I consider myself a pretty handy guy (albeit young), but with an engineering degree so I don't mind getting into some work on this as long as it can save me some cash.

Thanks!

fierohink

Your 4wd should engage by either pushing the multi mode button on the transfer case shifter, or moving the transfer case shifter to 4Hi or 4Lo.

Once a shift is requested, the 4wd ECU verifies the shift via sensor inputs on the transfer case and front diff. If these sensor outputs don’t match, the 4 green wheel light indicator should BLINK on the dash.

Since you said they aren’t blinking (indicating a position error) that leads me to believe the fuse is bad or the 4wd ECU is bad.

I’d like to believe a dealer tech checked fuse. Still check all your fuses to make sure they have continuity across both sides. Next I would check the position switches. The culprit is almost always the one on the front diff. Check it with a multimeter to ensure smooth operation and conductivity throughout the ENTIRE plunger range and doesn’t have any dead spots. Next check the position switches on the transfer case. The two on the actuator are the easiest to reach. Next check the contact traces inside the actuator, carefully remove the round cover with the 3 bolts and clean the contacts inside as needed. Check the write-up in my build thread for my ‘99 for some pictures.

prescott97

Thanks for your reply!

I didn't mention before, but the first thing I did was check all my fuses (not just if they are blown, but actually with a multimeter for continuity).

Interesting you say the 4WD ECU, would that not be something the dealership troubleshooted first?

I'll look a bit more into the position switches, thanks!

Malcolm99

I thought the 1997 didn't have the 4x4 picture in the centre of the cluster that flashes for position error and 4WD or 4Hi locked positions, isn't it just a green 4x4 indicator on the lower right corner. Have you gone under the truck to see if the front drive shaft is engaging at the transferase, if so you should look into the front diff actuator, have you tested to see if it is engaging 4x4 and the position switch on the front diff or case is not recognizing it and stopping the indicator from turning on.

prescott97

Not sure about the flashes, but yeah the 97 limited has the green 4WD indicator in the lower right corner of the dash. As for verifying if it is engaging, I switched the vacuum lines so that vacuum was supplied to the 4WD tube and drove around in the snow and could not feel the 4WD. Also, the note the dealer gave says the transfer case does not engage 4WD

Malcolm99

Confirm the dealers diagnosis, that could be a generic description of the problem, look under the truck to see if the tcase front drive shaft spins when you pull forward, no spin Tcase actuator problem, or you could engage 4x4 and see if the front drive shaft is locked to the tcase, if it spins when you pull forward it is either tcase or front diff actuator or position sensor problem. So find out if the front diff or the tcase is locking into it position, it might be easier to jack up the truck to do this but the wheels need to turn in order for the gears to line up and make engagement, then you can confirm which of the 2 is engaging.
try to narrow it down so you can isolate the problem area atleast.

power10er

Same vehicle and I am having very similar issues. 4wd will not engage. I get nothing when I press the push button on the shifter. No usual click from the relay/ecu and no actuator running sound either. The indicator light does not come on. The 4wd fuse is good. I verified the front axle does not lock in (spins freely). The VSV’s do not swap automatically, but I don’t think they’re ever getting the signal to swap since nothing happens from the push button. I did verify that the front axle does lock in when I manually swap the vacuum hoses at the VSV’s. (Does not spin)
I am leaning towards it being my 4wd ECU as the issue. Any other advice would be appreciated.
also, help me locate the 4wd ECU!!! Resources are sketchy on that.

thanks,
Brian