What Does Service 4WD Mean? Triggers, How to Clear, and More

The Service 4WD message or light appears when there’s a possible issue in the 4WD system that may require immediate attention. In this article, we’ll do a quick overview of what the Service 4WD message means and give drivers who are new to auto repair an idea of what clearing this warning light might entail.

What Triggers the Service 4WD Message?

Several issues can trigger the service 4WD message. The most common culprit is an incomplete shift in gears. Other possible causes include electrical or sensor problems and a malfunctioning or overheated transfer case.

Incomplete Shift in Gears

An incomplete shift in gears may trigger the 4WD service light to flash. This typically happens when you switch from 2WD to 4WD while the vehicle is still in motion, preventing the gears from fully engaging.

The transfer case transfers power from the transmission to the axles via the drive shaft. An overheated case will have difficulties transferring the needed power, triggering the message.

Wiring, Electrical, or Sensor Problems

Since modern vehicles are made up of complex interwoven cables and mechanical parts, damaged wiring is one of the most common causes of the service 4WD message.

These wiring issues can often be traced back to the transfer case control module (TCCM). Some of the common fault codes stored within the TCCM are:

• P1867: Transmission Transfer Case Contact Plate General Circuit Failure
• P1875: Transmission Automatic Hall Effect Sensor Power Circuit Short To Battery / 4WD Low Switch Circuit Electrical
• P1860: TCC PWM Solenoid Circuit Electrical / Transmission Transfer Case Contact Plate ‘D’ Short Circuit To Battery
• P1887: 4-Wheel Drive Control Solenoid Circuit Failure

In addition, the 4WD system has different sensors to help operate the system efficiently. Some of these sensors include the wheel speed sensor, transmission speed sensor, and throttle position sensor.

The wheel speed sensor detects the speed of the wheel and provides that information to the anti-lock braking system (ABS). This system prevents the wheel from skidding due to loss of control.

Meanwhile, the transmission speed sensor measures how fast the input and output shafts of the transmission are spinning.

And lastly, the throttle position sensor measures how open the throttle valve is and controls the air that flows into the engine intake manifold. The manifold will then supply the proper air and fuel ratio to the cylinders to generate power.

The Service 4WD message flashes if any of these sensors isn’t working properly or is sending a reading outside the normal range. Corrosion and exposure to the elements are two common reasons for any damage or malfunction.

Worn-out Components

Some vehicles (mainly older ones) use locking hubs to disconnect the front wheels from the front driveshaft. Similarly, modern car models have advanced electronics, such as the anti-lock braking system, to apply the brakes to skidding wheels.

Damage to either of these two supporting components may trigger the service 4WD message. The damage to locking hubs is often due to mud and rust buildup.

Meanwhile, the ABS may malfunction when metal shavings are attracted to the magnet wheel sensors. The shavings may come from the on-car-lathe, a machine used for resurfacing brake discs or rotors. It is not, however, a common phenomenon.

Another component that works with the 4WD system is the differential axles. They let your wheels rotate at different speeds. Damage to even one of these axles could compromise the entire system.

The easiest and most avoidable way of damaging the axles is by staying away from mud and water. The vent tube of the axle may suck up the water, which can lead to a failing differential.

Low/Contaminated Fuel Level

Driving in four-wheel-drive mode uses more fuel. As such, low fuel levels or contaminated fuel may occasionally trigger the message.

In this case, you can simply refill your gas tank to clear the code. Since the message could stem from more than one issue, it’s best to also check for other symptoms.

How to Clear the Service 4WD Message

Each manufacturer may have different procedures for clearing this warning light. Therefore, it’s best to research vehicle-specific information before making any attempts at troubleshooting your ride.

However, there are two simple steps you can do at home to try to clear the message:

Step 1: Check the Owner’s Manual

The owner’s manual should have information about what to do if the Service 4WD message is illuminating. Always refer to yours before attempting to diagnose or fix your vehicle.

Step 2: Engage and Inspect the 4WD system

Engage the 4WD system to see if it’s engaging when activated. This step is also a way to check if the message was a false alarm. If not, then the issue may lie elsewhere.

It’s best to leave the more complicated repairs to a professional. Here’s an overview of what a mechanic might do to clear this service message:

Step 3: Visual Inspection

A visual inspection is performed to check if there is any visible damage to the vehicle that might cause the code.

Step 4: Disconnect the Battery and TCCM

Disconnect the battery to reset the onboard system to see if that clears the message.

Before doing this, the engine must be switched off. Remove the negative cable from the battery terminal using a wrench, and wait for anywhere between 15 minutes to an hour before reconnecting the cable.

If it doesn’t, try unplugging the transfer case control module directly in an attempt to reset the system.

Step 5: Remove the Knee Bolster and Dash Bezel

The knee bolster is a component located under the steering column, while the dash bezel is the piece surrounding the gauges and instrument cluster on the 4×4 dashboard.

These two need to be removed to check the switches and wires of electrical components for any damage, which could be triggering the warning light.

Step 6: Check the Transfer Case and Transfer Case Control Module

Check the transfer case for fluids, leaks,  the hubs, and the linkage between the case and the 4WD control lever. Look at the fuse box to see if any fuse needs replacement.

If the warning message wasn’t triggered by an electrical problem, the next step is to check the transfer case control module. This component facilitates the power distribution to the front and rear axles in a 4WD system. It also collects input from switches as well as readings from various sensors.

Use a diagnostic scanner to read and resolve any of the codes that show up. Afterward, the control module is tested by commanding it to engage and disengage the transfer case while monitoring the system’s response. In some cases, the TCCM may need to be replaced.

Step 7: Check the 4WD Control Module

If the transfer case and TCCM are in good shape, check the 4WD control module next. This step may only apply to some vehicles, as some models have 4WD control modules that are also the TCCM.

First, inspect the 4WD system for any physical damage or loose wiring. Scan the system for codes and resolve any that show up. Afterward, check the module’s power supply by testing the voltage and resistance of the wiring and connections using a multimeter.

If everything is clear, the module’s outputs and inputs are tested using a diagnostic scan tool, multimeter, or oscilloscope. Lastly, the system is tested by engaging and disengaging it while it’s monitored.

Once your mechanic is done checking the control module, they’ll reinstall all the knee bolster and dash panels.

Step 8: Perform a System Reset

The last thing to do is to check if the Service 4WD light/message disappeared. If it’s still present, they may need to reset the 4WD system and other control modules. In some cases, they’ll even reset the onboard computer.

Can I Still Drive With the Service 4WD Light On?

Your vehicle will still move even if the service 4WD light is on. However, it could lead to transmission issues and damage to the all-wheel drive system. In any case, it’s best to take your vehicle to a mechanic as soon as possible.