Colorado buff
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I have the same issue took it Into shop. Vacuum hose and other two rubber hoses need to be replaced.
4wd Light Doesn't Turn On 4H
- Thread starter vtrunnin
- Start date
Sorry to revive an old thread, but I’m a bit lost. I have a ‘96 sr5 with the J-shifter.
4wd light was not coming on when we bought it. Checked the VSV hoses and they switch sides as they should. Also checked their electrical connectors.
Next, I verified that the transfer case was working by checking to see if I could turn the propeller shaft and it will spin freely in 2wd, while not being able to spin by hand in 4wd. This led me to believe the ADD switch is probably the culprit. I tested the old switch by removing it and using a multimeter to check for continuity upon pressing the switch. It tested bad so I replaced it with a new oem switch which tested fine before installation. I also tested the ADD switch connector to make sure it was getting power when switching to 4wd, and it did.
Needless to say, the light was still not working so I started testing to see if the TC switches were receiving proper signal. When I shifted into 4wd with the driver side TC switches unplugged, the light magically came on. I plugged them in and tried it and it stopped working. It then came on again with them plugged in, but it only happens every so often.
The thing that threw me off about the TC switches is that I got power to the neutral switch when I put it in 4hi (rear driver side switch). Is this normal? I assume one of the switches are bad, but would like some input before I start attacking those. Also, I have checked the 4wd fuse but not the ADD relay because I’m unsure of the location. Any and all help is appreciated!
4wd light was not coming on when we bought it. Checked the VSV hoses and they switch sides as they should. Also checked their electrical connectors.
Next, I verified that the transfer case was working by checking to see if I could turn the propeller shaft and it will spin freely in 2wd, while not being able to spin by hand in 4wd. This led me to believe the ADD switch is probably the culprit. I tested the old switch by removing it and using a multimeter to check for continuity upon pressing the switch. It tested bad so I replaced it with a new oem switch which tested fine before installation. I also tested the ADD switch connector to make sure it was getting power when switching to 4wd, and it did.
Needless to say, the light was still not working so I started testing to see if the TC switches were receiving proper signal. When I shifted into 4wd with the driver side TC switches unplugged, the light magically came on. I plugged them in and tried it and it stopped working. It then came on again with them plugged in, but it only happens every so often.
The thing that threw me off about the TC switches is that I got power to the neutral switch when I put it in 4hi (rear driver side switch). Is this normal? I assume one of the switches are bad, but would like some input before I start attacking those. Also, I have checked the 4wd fuse but not the ADD relay because I’m unsure of the location. Any and all help is appreciated!
phattyduck
Elite Member
Assuming you have an auto trans, since you mentioned the TC neutral switch... That only turns on the "ATP" light on the dash, but it is powered whenever the key is "ON" from the gauge fuse 'through' the ATP bulb on the dash. A multimeter will see 12V on the Red-Green wire unless the TC is in the Neutral position when it should be ground. It doesn't do much else (it is connected to the ECU, but nowhere else).
You should be able to hear the ADD relay click in the passenger footwell when you shift in and out of 4WD (truck ON, of course). The ADD relay swaps power between the two ADD VSVs on the fender well, which swaps vacuum on the ADD actuator. The 4WD light only turns on once a ground comes from the position switch on the front diff. That sounds like the last place you need to look. That switch can stop working or the actuator can be sticky and slow to engage...
To recap:
- shifting to 4WD should close the 4WD switch on the transfer case
- TC 4WD switch powers the ADD relay coil
- ADD relay swaps power/vacuum on ADD vacuum lines
- ADD vacuum actuator moves ADD actuator/sleeve
- ADD position switch shorts and turns on 4WD light (TC 4WD switch and ADD position switch are in series - both need to work and be closed for light to come on)
-Charlie
You should be able to hear the ADD relay click in the passenger footwell when you shift in and out of 4WD (truck ON, of course). The ADD relay swaps power between the two ADD VSVs on the fender well, which swaps vacuum on the ADD actuator. The 4WD light only turns on once a ground comes from the position switch on the front diff. That sounds like the last place you need to look. That switch can stop working or the actuator can be sticky and slow to engage...
To recap:
- shifting to 4WD should close the 4WD switch on the transfer case
- TC 4WD switch powers the ADD relay coil
- ADD relay swaps power/vacuum on ADD vacuum lines
- ADD vacuum actuator moves ADD actuator/sleeve
- ADD position switch shorts and turns on 4WD light (TC 4WD switch and ADD position switch are in series - both need to work and be closed for light to come on)
-Charlie
So it sounds like it’s one of the TC 4wd switches, considering I’ve confirmed all vacuum is working as it should and the ADD switch is new and functioning properly. With that said, can anyone give me some advice on a way to remove the TC switches for testing? I’ve read that most people drop the transmission crossmember to droop everything enough to get in there. Is that the best/easiest way or has someone found a workaround that may be more efficient?
phattyduck
Elite Member
There are three switches on the TC for a an auto j-shift. 4WD, 4LO and Neutral. 4LO is used by the ECU for updated trans shift patters. Neutral is is used for the ATP light on the dash. Only the "4WD" switch matters. Make sure you are testing/fixing the correct one.
Do you hear the ADD relay click when you move the shift lever in/out of 4WD? If so, the switch on the transfer case is working. How have you verified ADD actuator operation?
-Charlie
When checking the vacuum lines on the VSV, I was able to lock the front driveshaft (in “2wd”) by switching the lines which I would assume meant the ADD actuator is doing its job. Is this the correct procedure?
I will be able to work on it tomorrow, so I will test the 4wd switch to confirm proper function as well.
phattyduck
Elite Member
Yes, that means the actuator is working. Then you need to make sure the ADD position switch is also working - you can get to it next to the ADD actuator or up on the connector where it follows the vacuum lines up to the VSVs (both from the bottom)
-Charlie
Yes, that means the actuator is working. Then you need to make sure the ADD position switch is also working - you can get to it next to the ADD actuator or up on the connector where it follows the vacuum lines up to the VSVs (both from the bottom)
-Charlie
I replaced the switch already because it was testing bad. Tested the new one before putting it in and it worked as expected.
Got to the 4wd switch on the passenger side of the TC and it tested ok. I suspect that it may need cleaned which I will do when I get the chance. 4wd light illuminates on the dash now, but it is not 100% of the time. I’m thinking the 4wd relay on the passenger side may be part of the problem because there are times when I don’t hear it click, although it will the majority of the time. Is it possible to find a replacement relay? If so, I’ll just order a new one and a new 4wd switch just to cover all bases. If it’s not the switch or the relay then I’m really not sure where else to check.
phattyduck
Elite Member
Agreed! It sounds like you are on the right track, though probably with a bit more expense that might have otherwise been needed.
No, keep that 4WD system exercised in the future! Even the j-shift models can have problems if not used semi-regularly...
-Charlie
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