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Freightliner M2 Problems: 25 Common Faults & Fixes!

Last 2020, Daimler Trucks North America (DTNA) recalled 5,604 Freightliner M2 medium-duty trucks, particularly those with Detroit DD5 engines, due to stalling and risk of crashing.

Because of that, you can assume that the Freightliner M2 often encounters several faults, although most may not be as severe as those mentioned above.

In this article, you will learn about common problems in Freightliner M2 trucks and how to fix them.

Here are Common Freightliner M2 Problems to Expect:

The common mechanical problems in a Freightliner M2 include faulty transmission, steering, and AC components. Common Freightliner M2 electrical problems include a defective blower motor, heater, engine fan, horn, power-take-off (PTO), bulkhead module, instrument cluster, and cruise control.

Freightliner M2 Transmission Problems

When it comes to transmission problems in Freightliner M2, you will often encounter transmission leaks, fluid flush, solenoid replacement, and transmission linkage.

Transmission leaks occur if there is a bad gasket, broken drain plug, cracks in the fluid lines, damaged torque converter plug, faulty transmission pan, and leaky seals.

Repair or replacement of any of these parts will solve the problem.

If the problem is transmission fluid flush, it means that it drains all the fluids inside. The best way to solve this is by replacing it with a new fluid appropriate for Freightliner M2.

For problems in the solenoid and linkages, the best solution is a replacement or ensure that you tighten the transmission linkages.

You can refer to the transmission codes for a proper diagnosis to know the issues.

Freightliner M2 Steering Issues

Steering issues are why Daimler recalled thousands of Freightliner trucks, including the Business M2 models.

Some drivers experienced difficulty when steering left or right. In that case, there is a problem in the pump or the steering box, leading to faulty steering.

To fix steering issues, the truck needs to undergo a pump test to confirm the box can move upward and downward without any problems.

If there is not, replacing the faulty parts and retaking the pump test will verify if you already fix the issue.

Freightliner M2 Electrical Issues

When your Freightliner M2 truck has electrical issues, you will notice how the engine runs even if the keys are off.

The ABS, brake lights, tail lights, parking brake, and warning sirens may also go haywire.

In this case, you must check if every plug is in the proper connection. If not, fix the wiring to prevent encountering other problems.

Freightliner M2 AC Issues

A leaking compressor is one of the most common AC issues in Freightliner M2.

Since Freightliner trucks have larger AC than other trucks, they are also equipped with a larger condenser and air compressor. Thus, they are more prone to encounter problems.

You must bring your truck to a mechanic immediately to fix AC issues. But you can perform troubleshooting to confirm the problem first and save you from additional expenses.

To troubleshoot, you need to turn the engine on to warm it to its average temperature. The AC will work well if it is warm enough inside.

Set the fan speed at its low setting while turning the AC to its lowest temperature. As you do this, you should hear a soft humming sound in the compressor.

If not, there is a possible leak on it, and you should consider replacing them.

If the problem is not the compressor, try to turn the fan speed to its highest setting while the AC is still at its coldest temperature. You need to recharge the AC system if no cold air comes out.

Freightliner M2 Blower Motor Not Working

There are two possible reasons for encountering problems with the blower motor.

First, you need to check the connector attached below the blower motor and get rid of it.

The second one is the fuse box. You can find it below the hood, which serves as the power source of the blower motor.

Unplug the fuse box from its connector. Remove and replace if there are signs of burned wiring or corroded pin.

Freightliner M2 Heater Not Working

It’s hard to drive in cold weather if the heater on your truck is not working well.

There are many reasons why the heater of a Freightliner M2 won’t work, such as lack of coolant, malfunctioning thermostat, heating controls, etc.

To fix the heater, you must first check the reason for conducting the necessary repair.

For example, if the problem is a lack of coolant, you must refill it. If the thermostat and heating controls need to be fixed, you can buy and install a new one.

Freightliner M2 Engine Fan Not Working

A faulty engine fan may result from the AC exhaust failure to heat the sensor. You should also check for possible leakage.

You can try to replace the solenoid, which you can find on the firewall. Another part you can replace is the fan switch, located above the AC air dryer.

Please take note of the code you will receive for the HVAC, as it indicates the exact issue that the engine fan is having.

Freightliner M2 Horn Not Working

Horns are essential for giving signals or warnings while on the road. Accidents can occur if it does not work well.

The horn button in the steering wheel is not directly connected to the electrical circuit linked to the horn.

The signal from the horn button comes from the bulkhead module. It will then process the command allowing the horn to blow.

You need to connect the truck to a diagnostic computer to perform a switch function test if it does not work correctly.

It will allow you to ensure that the bulkhead module can see or detect the horn button once you press it.

Freightliner M2 PTO Not Working

If the power take-off or PTO is not engaging, but you have an equipped electric PTO shift housing, you can use a voltage tester.

It will help you confirm the voltage the solenoids receive to the PTO. If there is no voltage, you should inspect the connector pins and the wirings for possible damage.

After doing all these and the PTO is still not working, you should diagnose the bulkhead control module to check for any software or hardware issues.

Freightliner M2 Bulkhead Module Problems

Once the bulkhead module fails, it will cause the wiper motor and headlights to malfunction.

You can reflash the bulkhead module. If the problem persists, there is a possible miswiring on the harness.

You can also see codes appearing, such as the S82/6 and 6897/6. These codes mean too much current in the fuel water separator heater.

Freightliner M2 Instrument Cluster Not Working

It is common to encounter frequent issues with the Freightliner M2 instrument cluster or the dashboard.

The most common issue that you can experience involves the speedometer or tachometer.

These gauges are possible to malfunction over time. Thus, you may need to reset them to see if they will still work.

To do it, turn the key off first for about 10 seconds. After that, please turn it on again. Repeat the same procedure three times.

Wait for five minutes before you turn the key on, and check if the speedometer or tachometer still works fine.

If either of them still malfunctions, consider repairing them, which may cost you around $100 to $400, depending on the exact issue.

Freightliner M2 Cigarette Lighter Not Working

A problem with the cigarette lighter can be fixed by repairing the broken fuse in the bulkhead module.

The bulkhead module serves as the control power of the cigarette lighter, running lights, and wipers. Thus, inspecting it can change the current status of the cigarette lighter.

Freightliner M2 Cruise Control Not Working

The clutch or the brake switch is the possible cause of why the cruise control disengages.

In that case, try pulling the pedals up to see if it will work. Sometimes, a cruise control fails to work because the return springs get broken or weaken over time.

Freightliner M2 Windows Not Working

The electronic windows of a Freightliner M2 are a bit annoying to deal with since it always happens unexpectedly.

You should check if the problem is either the switch or the motor. Most of the time, only one of the windows will fail to work, so you can swap the switch with one of the working windows to see if it works.

If it is, then it is indeed the switch. If not, then it is probably the motor.

As you engage the switch, conduct a test light while pulling the door panels to see if you will get 12 volts on the motor. If yes, get a hammer to tap it. Then check it will engage and start working.

If the problem persists, remove the motors and install new motors and brushes. The replacement may cost you around $30 to $150.

Freightliner M2 Brake Lights Not Working

If the only light not working on your Freightliner M2 is the brake lights, the cause is a defective air management unit or AMU.

To fix it, look for the AMU found on the frame cross member near the rear axle. The AMU is the switch right of the cluster or on the driver’s side.

The repair cost for the AMU is around $250.

Freightliner M2 Headlight Not Working

Low voltage or VBAT1 is the problem of a faulty headlight.

The output circuits that VBAT1 powers will not work since there may be other fault codes. Thus, troubleshooting will confirm it.

Check the Power Distribution Modules (PDM) circuit if it is open. Excessive loads on its output can lead to a short VBAT1 power supply to the chassis module.

As you turn on the key, test all the fuses to see if there is power on both sides. If there is only one, replace the other.

Always inspect the connector pins and wiring harness to avoid damaging the lighting circuits, which results in faulty headlights.

Freightliner M2 Turn Signal Problems

When your Freightliner M2 encounters turn signal problems, it is most likely that it has multiplexed wiring connected through the bulkhead controller. Thus, it can result in fault codes for turn signal problems.

If you connect the headlight, wiper motor, and turn signal to only one switch, one will surely malfunction.

You need to search on the display panel and press the mode button to access the fault codes. Once you know the code, it is easier to diagnose correctly.

Freightliner M2 No Marker Lights

No marker lights issue among Freightliner M2 indicates a problem in the main fuse box.

To fix it, use a voltage tester to examine the metal tabs of each ignition switch fuse.

If everything is okay, scan the bulkhead module and check the fault codes. There is more likely that the issue is software-related.

Aside from these, you may also check any damage within the wiring and harness that may cause a short circuit.

Freightliner M2 Radio Not Working

Faulty wirings also cause a malfunctioning radio.

All you need to do is check for any loose wires. Or better yet, change anything already worn out.

Aside from faulty wirings, it can also be the fuse box. Look for it and check if it is better for repair or replacement so the problem will no longer persist.

Freightliner M2 Wipers Not Working

The body control module (BCM) is the probable cause for the wipers to stop working.

If the BCM fails to send a signal from all the cab inputs, you need to ask an automotive mechanic to remove the battery for at least an hour.

Most of the time, the wiper will start working again after that troubleshooting method.

If not, you need to connect to the Freightliner service link to command faulty circuits. You will see better if the issue lies in the BCM, input circuit, or output circuit.

Freightliner M2 Not Building Air Pressure

Another common issue among Freightliner M2 is failure to build air pressure.

The most probable cause is that the unloader valve may be stuck. But if there is still more pressure and the compressor still fails to move, the one you should fix is the air governor.

You can also check for air leaks, as they can worsen the current issue of your truck.

Freightliner M2 Won’t Crank

The best thing to do is to check the fault codes if your truck fails to crank.

The most common reasons why it happens are the mechanical engine system is not responding or misaligned, issues with the bulkhead module, and missing smart switch.

You can only program the smart switch into the bulkhead module using the Freightliner software.

To find which smart switch has a missing signal, you need to check all the switches to see if there are any loose connections or damaged wirings.

Freightliner M2 Cranks But Won’t Start

If your truck cranks but fails to start, check the fuel line, as the inlet and the fuel filter outlet can be loose.

Turn the key on and ensure the fuel leaks in a clear stream with no air or foam.

Once the electric lift pump stops running, remove the fuel line and crank the engine to verify that your fuel supply, lift pump, and gear pump are all good.

Freightliner M2 DEF & DPF Problems

Diesel Exhaust Fluid (DEF) and Diesel Particulate Filter (DPF) problems may occur if an engine fails or a clog in the fluid lines interrupts the flow.

You can bring your truck to an automotive shop to clean and remove the clog. Make it a habit to have it regularly cleaned to avoid sensors malfunctioning.

Freightliner M2 Regen Problems

There are many reasons why a truck has regen issues. The most common ones are clogged DPF, EGR fault codes, and the VGT turbo operation.

If it occurs, you need to inspect the check engine light (CEL) since it can disable the process of DPF regen. If it happens, it will lead to an engine shutdown.