At Fixya.com, our trusted experts are meticulously vetted and possess extensive experience in their respective fields. Backed by a community of knowledgeable professionals, our platform ensures that the solutions provided are thoroughly researched and validated.
Changed the vacuum actuator. changed the electric shift motor on the transfer case. changed the vacuum switch on the transfer case. went into 4wd easily. drove a little. stopped. pushed 4wd low button. went in but lights flashed and the transmission would not shift out of low gear. as i slowed down it shifted back into 2wd with a clunk and now will not go into 4wd but sometimes into low with lights flashing. possibly drive line computer under kick panel? thanks. Jeff
I can feel the transmission shifting and transfer case changing to low and back to high ,I can see the actuator moving in and out but the front wheels don't engage. gears are good in nthe differentialI can feel the transmission shifting and transfer case changing to low and back to high ,I can see the actuator moving in and out but the front wheels don't engage. gears are good in nthe differential
You can't post conmments that contain an email address.
- If you need clarification, ask it in the comment box above.
- Better answers use proper spelling and grammar.
- Provide details, support with references or personal experience.
Tell us some more! Your answer needs to include more details to help people.You can't post answers that contain an email address.Please enter a valid email address.The email address entered is already associated to an account.Login to postPlease use English characters only.
Tip: The max point reward for answering a question is 15.
If the switch was in the 2WD position and the transfer case was locked in a 4WD range, my 2 SWAGs would be bad switch or the connector to the shift motor is damaged / corroded or the fuse to the transfer case shift relay module is blown ( fuse # 17 ) / problem with the transfer case shift relay module.
This is without knowing if the truck was used in 4WD the night prior, and shifted out just before turning off. If this is the case, the shift motor might be stuck, and a few hits with a dead blow hammer to the transfer case might jar it free again ( do not use a metal hammer, it could damage the transfer case ).
The vacuum shift solenoids on the firewall are controlled by the GEM ( Generic Electronic Module ) which is grounding either the 2WD or 4WD solenoid, depending on the shift plate contacts in the transfer case. ( when in 4 or 4H, the contact switch plate signals the GEM, which in turn grounds the correct solenoid ).
Pulling the switch will not cause the transfer case to go back to a default position, the switch has a resistance level for each mode, and needs that value to operate the shift motor.
The resistance values for the switch between the 2 dark blue wires: 2WD - 4100 to 3700 ohms 4H - 1050 to 1150 ohms 4L - 380 to 340 ohms - find the wire locations on the switch, mark them and remove the connector to test the resistance.
Just my opinion on the order :
1. Check the fuses for the shift motor 2. Try the old school shift method, back up ~ 50' put into park or neutral, and shift from 4WD to 2WD. 2.1. This is to see if the transfer case shift motor is bound up, and reversing might release it 3. Try hammering the transfer case with a dead blow hammer while someone shifts from 2WD to 4WD. You only need the key in the run position, if it happens quick enough after running the engine, the vacuum reservoir will still have enough vac to operate the solenoids. Don't chance running yourself over. 3.1. If this frees up the shift motor and the vacuum has bled off, you can try starting the truck and shifting into 4H then back to 2WD to get the front axle to disconnect or manually vacuum operate the front disconnect motor by applying vacuum to the pink vacuum line on the shift motor on the front axle.
This is something you can do yourself if you have ever worked on a vehicle before. The part you need is called a front drive actuator valve. It costs about $ 50.00, GM part # 15165891.
Here is some more infor about it:
Main 4wd Components: TCCM - Transfer Case Control Module - Located behind the glove box. This is the electronic 'brains' behind the shifting. Switch - The push button switch in the dash - driver input/indicator. Encoder Motor - Located on the transfer case - This is what actually shifts the transfer case, and tells the TCCM what position it is in. Vacuum Switch - Also located on the transfer case - This is what sends vacuum to the vacuum actuator (see below) when the transfer care is in 4HI or 4LO. Vacuum Actuator - Located under the battery tray - This is what engages or disengages the front driveshaft. Front Axle Switch - Located on the front axle - This is what tells the TCCM when the front axle is engaged.
If you want to try and replace it yourself, please let me know how it goes.
I HAD A BLAZER WITH THE SAME SYMPTOMS REPLACED THE TRANSFER CASE MOTOR AND SOLVED PROBLEM. TRANSFER CASE MOTOR SHIFTS FROM HIGH TO LOW GEAR IN THE TRANSFER CASE AND TELLS THE FRONT ACTUATORS TO INGAGE FRONT HUBS . MOTOR WON'T MOVE TO 4 HIGH AND GRINDS WHEN TRYING TO MOVE TO 4 LOW, TRANSFER CASE MOTOR FAILING . CHECK VACUUM LINES AND ACTUATORS ON FRONT DIFF THEY FAIL, CAN CHANGE TO CABLE ENGAGEMENT INSTEAD OF FAILURE PRONE VACUUM ACTUATORS.
On the full size, the front actuator is electric, not vacuum.
When in 4wd mode, a switch on top of the transfer case conducts 12
volts out to the actuator. Wire #50 (brown) is the 12v feed, and it
conducts to the light blue wire (#900) to the actuator. When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the
front differential - it looks like a large bullet that threads into the
front diff.) If it has 12 volts, the actuator is the problem. If it
does not have 12 volts, check the transfer case switch and the power
feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd. The way this actuator works, is it is a sealed chamber that gets heated
by voltage. When it heats, the pin in the end swells and pushes a shift
fork in the front differential. The shift fork engages a spline on the
passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a
heated device. However, it requires a small harness addition, a spacer,
and a new actuator. It is about a $150 to $200 option.
Good
luck. The actuator is usually the problem 90% of time but recheck all
of the wire harness just to maker sure there is no short before
replacing any parts.
88-UP C/K ACTUATOR UPGRADE VEHICLE SERVICED: 1994 CHEVROLET FULL SIZE PURPOSE: IMPROVE AXLE CONNECT ENGAGEMENT TIME
AND
COMPONENT RELIABILITY.
SYMPTOMS: NO FRONT DRIVE AXLE ENGAGEMENT WHEN SHIFTED
INTO 4X4.
Obtain the following GM part numbers:
(1) 26060073 Actuator
(1) 88959465 Harness/Spacer Kit
On the full size, the front actuator is electric, not vacuum.
When in 4wd mode, a switch on top of the transfer case conducts 12
volts out to the actuator. Wire #50 (brown) is the 12v feed, and it
conducts to the light blue wire (#900) to the actuator. When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the
front differential - it looks like a large bullet that threads into the
front diff.) If it has 12 volts, the actuator is the problem. If it
does not have 12 volts, check the transfer case switch and the power
feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd. The way this actuator works, is it is a sealed chamber that gets heated
by voltage. When it heats, the pin in the end swells and pushes a shift
fork in the front differential. The shift fork engages a spline on the
passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a
heated device. However, it requires a small harness addition, a spacer,
and a new actuator. It is about a $150 to $200 option.
Good
luck. The actuator is usually the problem 90% of time but recheck all
of the wire harness just to maker sure there is no short before
replacing any parts.
Check the fuse to the 4x4, if the fuse is good then check the 4x4
electric motor actuator on the transfer case. You should hear it work
from 2wd, 4hi to 4low and back to 2wd with the push of the switch. if
you don't hear it working then check the wire harness at the actuator
motor, look for any damages like corrosion or cracked wire connector
clips. If the 4x4 actuator is working on the transfer case. There is
a vacuum switch on the top of the transfer case, driver side but when
that fails, your front hub stay's locked in the on position. Good luck
and keep me posted and hope it's a simple fuse that has gone bad. You
can pick up all these parts at Auto Zone or Parts Source and they will
have the step by step instructions for you to get the job done with
common tools. Replacing the vacuum switch on top of the transfer case take about 15 min to replace if you don't have to jack up the Jimmy if not 30 min if you have to jack it up. Be safe and keep me posted, be glad to know your go it working again.
On the full size, the front actuator is electric, not vacuum.
When in 4wd mode, a switch on top of the transfer case conducts 12
volts out to the actuator. Wire #50 (brown) is the 12v feed, and it
conducts to the light blue wire (#900) to the actuator. When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the
front differential - it looks like a large bullet that threads into the
front diff.) If it has 12 volts, the actuator is the problem. If it
does not have 12 volts, check the transfer case switch and the power
feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd. The way this actuator works, is it is a sealed chamber that gets heated
by voltage. When it heats, the pin in the end swells and pushes a shift
fork in the front differential. The shift fork engages a spline on the
passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a
heated device. However, it requires a small harness addition, a spacer,
and a new actuator. It is about a $150 to $200 option.
If I were you, I would buy a new heated actuator. They are available at
most auto parts stores, and are about $90. They are also on eBay for
about $55 plus shipping. These are very easy to change - just thread out the old one, and thread in a new one.
Good luck, That actuator is usually the problem 90% of time.
Hi:
The main parts to the 4WD system are the transfer case, the shift control motor, and the shift control module. if you remove the shift control motor from the transfer case, and leave it plugged into the harness, you should be able to see if it functions thru all settings, such as 4wd high or low or 2wd. If not, then you need to figure out which part is bad, the motor or the control module. If it does work as it should, then you have some sort of transfer case problem.
On the full size, the front actuator is electric, not vacuum.
When in 4wd mode, a switch on top of the transfer case conducts 12
volts out to the actuator. Wire #50 (brown) is the 12v feed, and it
conducts to the light blue wire (#900) to the actuator. When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the
front differential - it looks like a large bullet that threads into the
front diff.) If it has 12 volts, the actuator is the problem. If it
does not have 12 volts, check the transfer case switch and the power
feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd. The way this actuator works, is it is a sealed chamber that gets heated
by voltage. When it heats, the pin in the end swells and pushes a shift
fork in the front differential. The shift fork engages a spline on the
passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a
heated device. However, it requires a small harness addition, a spacer,
and a new actuator. It is about a $150 to $200 option.
If I were you, I would buy a new heated actuator. They are available at
most auto parts stores, and are about $90. They are also on eBay for
about $55 plus shipping. These are very easy to change - just thread out the old one, and thread in a new one.
Good luck, That actuator is usually the problem 90% of time.
I can feel the transmission shifting and transfer case changing to low and back to high ,I can see the actuator moving in and out but the front wheels don't engage. gears are good in nthe differential
×