Troubleshooting the Toyota FJ80 Land Cruiser Center Diff Lock (CDL)

When I purchased my 1992 Toyota FJ80 Land Cruiser, the previous owner informed me that the four-wheel-drive system did not work. I knew the transfer case was a rebuilt unit so I figured it would be something simple such as a switch or a relay.

Little did I know that I would spend hours trying to troubleshoot the problem.

My goal with this article is to walk you through the diagnostics needed to check the Center Differential Lock (CDL) electrical system on the FJ80. I am not a professional mechanic, so please verify what I am writing. New information arises all the time, and better diagnostic articles may be available.

You might ask, why did you spend hours diagnosing the problem? My answer is, I don’t like to spend money on parts when the part being replaced was not the problem. I’ve been a victim of paying people to do just that. Never again.

As in all repairs on the Land Cruiser, you should purchase the factory Toyota Repair Manual and the Toyota Electrical Wiring Diagram for your specific year vehicle (order the factory manuals at techinfo.toyota.com). A Chilton’s or similar service manual won’t cut it when you are diagnosing particular issues. Invest the money in the factory manuals. It’s worth it if you (or your mechanic) does any diagnostics or repairs on your Land Cruiser. Purchasing the correct manual will pay off only after a few repairs because you will be diagnosing problems and not throwing parts at the problem until it is fixed. The reference for this article was the USA version for the 1992 model year Toyota Land Cruiser. 

The factory service manual is not the final word for diagnosing issues. Experience (or the experience of others) is a valuable asset to have when diagnosing problems on your vehicle. One of the best online resources that fill in the blanks where the Toyota factory manual leaves off is the 80-series on ih8mud.com. I think I would still be scratching my head over the CDL if it had not been for the wisdom contained in the 80-series forum on ih8mud.

The 80-series Land Cruiser Center Differential System

To make any repairs to the CDL, it’s a good idea to learn a little how the CDL system works on the 80-series Land Cruiser. I’ll try to use the terminology used in the Toyota Land Cruiser factory service manual (1992 model year).

The FJ80 Land Cruiser is a full-time four-wheel drive (4WD) system that is equipped with a mechanical lock type center differential system. During normal driving (CDL unlocked), the transfer case allows the driveshafts to turn at different speeds, so when you are turning on a hard surface, there is no binding. When you engage (lock) your CDL, it splits the power 50/50 to the front and rear driveshafts regardless of the surface you’re driving on or if you are turning. For a detailed explanation on how your 4WD system works, see Diffs for Dummies.

The CDL components visible from the driver’s seat include the instrument panel 4WD Indicator Light; center differential lock switch (stock only on 3FE powered 80-series in the US but can easily be added to 93-97 models) and the transfer case select lever.

The other components of the CDL system include the Center Diff Lock Control Relay; the 4WD Indicator Switch, the Transfer Neutral Position Switch; the Transfer L4 Position Switch; and the Transfer Control Motor Actuator.

The brain of the system is the Center Diff Lock Control Relay which is located inside the vehicle on the driver’s side kick panel. My relay was labeled Transmission Relay. Without this relay, you will not be able to engage the 4WD from your cab.

Refer to the wiring diagram to follow along.

Power to the CDL relay is sent from three separate sources. The first power source (Terminal 3 on the relay) is from the 30 amp fuse in the dash fuse box labeled “Diff.” This power source should be hot at all times the ignition is on. Within the CDL relay, this power is sent to two small internal relays – normally in the closed position. Input from the two switches described below will change the polarity to the Transfer Control Motor Actuator. The reversal of polarity on the actuator is what engages and disengages the transfer case.

The second power source (Terminal 7 on the relay) is from the Transfer L4 Position Switch (located on the top rear housing of the transfer case – right side). The Transfer L4 Position Switch receives its power from the 10 amp fuse located inside the passenger compartment fuse panel and labeled “Gauge.”

When you shift the Transfer Case Select Lever into low range, the L4 switch sends a signal to the CDL relay. This overrides the input from the Center Diff Lock Dash Switch which closes an internal relay. Power from Terminal 1 of the relay is sent through the harness to Terminal 3 of the actuator motor engaging the center diff lock (transfer case) into 4WD. If you have the Center Diff Lock Switch, you can disconnect this wire from the relay to have complete manual control over the CDL.. See Center Differential Lock Pin 7 Mod for specific instructions on this modification.

The third power source for the CDL relay comes from the Center Diff Lock Dash Switch. Power to the switch is from the same 10 amp fuse previously mentioned. When the switch is on (CDL engaged), you will have 12 volts to Terminal 6 of the CDL relay. When the switch is off, there will be 12 volts to Terminal 9 of the CDL relay. Turning the switch on sends 12 volts from Terminal 1 of the relay through the harness to Terminal 3 of the actuator motor. Turning the switch off sends 12 volts (reversing the polarity) from Terminal 4 of the relay through the harness to Terminal 2 of the actuator motor. The Center Diff Lock Dash Switch engages the CDL only when the center diff is in high range.

When you enage the CDL, either through the Center Diff Lock Dash Switch or through the 4 low range shift lever, the 4WD Indicator Switch (located on the front housing of your transfer case) is activated and provides a signal to the 4WD indicator light on your instrument panel. There is also a Transfer Neutral Position Switch (located next to the Transfer L4 Position Switch – drivers side) that provides a signal to the A/T indicator light on your instrument panel to tell the driver that the transfer case is in neutral.

Factory Service Manual Center Differential Lock Diagnostics

The first diagnostics outlined are from the Toyota Factory Service Manual (FSM). After that, I will discuss what Toyota left out of the FSM.

If you’re at this point, you’ve probably realized that the DIFF LOCK indicator light on the instrument cluster does not light up when you turn on the CDL switch or when you shift into 4L.

Before going too far in the diagnostics, some people actually have luck by only exercising the CDL (by shifting into and out of four-wheel drive) a few times to unstick the CDL. Of course, you need to make sure that the two fuses that provide power to the CDL circuit are in working condition. (Note to self – probably a good thing to carry as a spare.)

Two tests can be conducted to see if it is truly not working. First, find a gravel parking lot that you can turn tight circles in and make a full locked turn to the left. When the CDL is engaged and locked, you will see that the rear tires are slipping as the rear axle follows a smaller arc than the front wheels. You will also notice a difference in the steering and a larger turning radius. If this is not the results, the CDL may not be working correctly.

The next test is outlined in the FSM. With your rear wheels chocked, your transmission in neutral, your transfer case lever in high range and your CDL switch off, jack up your right front wheel off the ground. If the CDL is not engaged, this wheel should spin freely.

Next, engage your CDL dash switch or shift into 4L. With the transmission in neutral, you will not be able to rotate the lifted wheel when the CDL is activated. If the CDL does not engage, further diagnostics are required.

To proceed with the following diagnostic tests, you will need a multimeter that reads DC voltage, resistance, and continuity. I also recommend that you make a couple of test wires with alligator clips at each end. I made one wire red and the other wire black (negative and positive reference). You should also pick up a couple of standard size paperclips, a fresh 9-volt battery or two and some dielectric grease.

The FSM only outlines three tests. I will add a few later.

The first inspection from the FSM is for the Center Differential Lock Control Relay. This is the relay that is located on the driver’s side kick panel. To test the relay, remove the mounting nut with a 10 mm socket and then disconnect the relay from the harness. The FSM shows several continuity tests, with and without voltage applied to the relay.

With NO voltage applied to the CDL Relay, there will be continuity between terminals 1 and 2 and terminals 2 and 4. Between terminals 6/7, there is a diode that only allows for continuity in one direction. If you don’t get continuity the first time between terminals 6/7, reverse positive and negative leads, and recheck continuity.

Using your 9-volt battery and your positive and negative test leads, apply battery voltage to the CDL relay terminals as follows:

• Positive to 6 / Negative to 5 = Continuity 1/3, No Continuity 1/2
• Positive to 7 / Negative to 2 = No Continuity 9/10
• Positive to 9 / Negative to 10 = Continuity 3/4, No Continuity 2/4

The FSM states, “If continuity is not as specified, replace the relay.” The only test I disagree with the FSM is the continuity test between 6/7. If there is no continuity, even when reversing the polarity, it merely means that you cannot engage the CDL when you shift into 4L. If you have the CDL dash switch, this is your 7 Pin Mod already done. This is the case on my ’92 FJ80. Now for the later 80-series models without the CDL switch, this could be a problem. Just don’t run out and purchase a replacement CDL relay, buy the CDL dash switch instead. The CDL dash switch is much less expensive than the CDL relay.

Another test outlined in the FSM is the test for the CDL Dash Switch. Just pop out the switch from the dash and disconnect from the harness. With the CDL switch in the “OFF” position, there will be continuity between terminals 7/10. In the “ON” position, there will be continuity between terminals 7/10. If continuity is not as specified, replace the switch. I haven’t verified it, I did read somewhere that the 4-way flasher switch could be swapped in and used as a CDL switch.

The final FSM test for the CDL system is to inspect the Actuator motor. Using an ohmmeter, first measure the resistance between terminals 2 and 3. The standard resistance is between 0.3 and 100 ohms. Next measure the resistance between terminals 2 and 3 and body ground. Standard resistance should be more than 0.5 M ohm. If resistance is not as specified, replace the motor actuator.

What the Factory Service Manual Doesn’t Tell You

The previous CDL tests are all that is outlined in the FSM. The following CDL diagnostics are not in the FSM and are a summary of various resources found on the Internet.

Test DIFF LOCK Indicator Light and 4WD Indicator Switch

The DIFF LOCK indicator light not working (active when the CDL switch is on or when shifted into 4L) could be caused by a burnt-out indicator light, or the 4WD Indicator Switch is defective.

To test, with a paperclip in hand, crawl under the right side of your Land Cruiser and locate the 4WD Indicator Switch. The 4WD Indicator switch is located on the top front housing of the transfer case. Remove the harness from the switch and jump the terminals on the harness with the paperclip. With your ignition in the ON position, your DIFF LOCK indicator light should light up. If the DIFF LOCK indicator does not come on, you most likely have a bad bulb and it will need replaced. If the bulb is fine, you will need to remove the 4WD Indicator Switch and either free it up or replace it. I would first try to exercise, lubricate and test the switch before replacing it. Once the switch is removed, place the switch in a vise. Check the continuity between the terminals. When the switch is open, there should be no continuity and of course when closed (depressed) there will be continuity. If the switch is sticky, use some WD40 to clean and exercise the switch. This may or may not work but is worth a try before spending money on a new switch.

Test L4 Switch

The L4 switch is located on the top rear of the transfer case, right side (passenger side in the US). It appears to be the same switch as the 4WD Indicator Switch. If you remove the harness from the switch and use a paperclip to jump the harness, with your ignition switch ON, this test simulates shifting your transfer case into 4L and should power your actuator motor.

Test Actuator Motor

To test the actuator motor, arm yourself with a fresh 9-volt battery (do not use any higher voltage) and your test leads and crawl under the right side of your Land Cruiser and locate the actuator motor. Disconnect the actuator motor from the harness. Locate terminals 2 and 3 and attach the positive lead to terminal 3 and the negative lead to terminal 2 of the actuator motor. With voltage applied, you should hear the actuator motor run for a few seconds and stop, engaging the CDL. You will unlock the CDL by reversing the polarity on terminals 2 and 3. If the motor does not operate with the voltage applied, it’s most likely that the actuator motor is stuck.

The actuator motor can be removed while the transfer case is still in the vehicle. The trick is to get some long bolts to insert between the cross member and frame rail that allows the transfer case to be lowered. Once the transfer case is dropped, remove the breather hose and the four bolts that attach the actuator motor to the transfer case. You will most likely have to pry the motor off the transfer case.

Some people have been able to clean up and re-lube the actuator motor. I wasn’t so lucky. My actuator motor was fried and needed replaced. So back into the Land Cruiser and order a replacement. I was able to locate a used actuator motor for a fraction of the cost of a new unit. Once the replacement actuator motor was installed, it worked like a charm.