This guide walks you through step-by-step instructions to clear the service engine soon light on your E39 BMW M5. You’ll learn about diagnostic tools, common causes, and troubleshooting tips to keep your M5 running smoothly.
Key Takeaways
- Understand the cause first: The service engine soon light can indicate anything from a loose gas cap to a serious engine issue. Always diagnose before clearing.
- Use an OBD2 scanner: A compatible scanner is the most reliable way to read and clear fault codes on the E39 M5.
- Check common issues: Common triggers include faulty oxygen sensors, mass airflow (MAF) sensor problems, or ignition coil failures.
- Manual reset isn’t always possible: Unlike maintenance lights, the service engine soon light usually requires a scanner to reset.
- Battery disconnection is risky: While disconnecting the battery may clear the light temporarily, it can reset other systems and won’t fix the root problem.
- Clear codes after repairs: Always clear the light after fixing the issue to confirm the problem is resolved.
- Seek professional help if unsure: If you’re not confident diagnosing or repairing, visit a BMW specialist to avoid further damage.
How to Clear E39 BMW M5 Service Engine Soon Light
If you own a classic E39 BMW M5, you know how rewarding—and sometimes frustrating—it can be to maintain such a high-performance machine. One of the most common issues owners face is the dreaded “Service Engine Soon” light illuminating on the dashboard. While it might seem intimidating, clearing this light is often straightforward—if you know what you’re doing.
In this guide, we’ll walk you through everything you need to know about diagnosing, understanding, and safely clearing the service engine soon light on your E39 BMW M5. Whether you’re a seasoned DIY mechanic or a first-time BMW owner, this step-by-step guide will help you take control of your car’s health without unnecessary trips to the dealership.
What Does the Service Engine Soon Light Mean?
Visual guide about How to Clear E39 Bmw M5 Service Engine Soon Light
Image source: wikihow.com
The “Service Engine Soon” light—also known as the check engine light—is part of your BMW’s onboard diagnostic system (OBD2). When it comes on, it means the car’s computer has detected a problem with the engine, emissions system, or related components.
It’s important to note that this light is different from the “Service Interval” or “Inspection” light, which simply reminds you it’s time for scheduled maintenance. The service engine soon light indicates an active fault that needs attention.
On the E39 M5, common triggers include:
– Loose or faulty gas cap
– Failing oxygen (O2) sensors
– Mass airflow (MAF) sensor issues
– Ignition coil or spark plug problems
– Catalytic converter inefficiency
– Vacuum leaks
Ignoring the light can lead to reduced fuel efficiency, poor performance, or even engine damage over time. So, while clearing the light is easy, diagnosing the root cause is the real priority.
Tools You’ll Need
Before you begin, make sure you have the right tools on hand. Here’s what you’ll need:
- OBD2 Scanner: A basic code reader works, but a BMW-specific scanner (like an INPA, ISTA, or a high-quality Bluetooth OBD2 adapter with compatible software) gives more detailed readings.
- Smartphone or Laptop: If using a Bluetooth OBD2 adapter, you’ll need a device to run diagnostic apps like Torque Pro, Carly for BMW, or BimmerCode.
- Owner’s Manual: For reference on fuse locations and safety tips.
- Basic Hand Tools: Screwdrivers, pliers, and a socket set may be needed if repairs are required.
- Safety Gear: Gloves and safety glasses, especially if working under the hood.
Step-by-Step: How to Clear the Service Engine Soon Light
Now that you’re prepared, let’s get into the actual process. Follow these steps carefully to safely clear the light.
Step 1: Check the Gas Cap
Believe it or not, a loose or damaged gas cap is one of the most common causes of the service engine soon light. The cap seals the fuel system, and if it’s not tight, fuel vapors can escape, triggering an emissions fault.
- Turn off the engine and let the car cool.
- Open the fuel filler door and unscrew the gas cap.
- Inspect the cap for cracks, worn rubber seals, or damage.
- Reinstall the cap and turn it until you hear it click 3–4 times.
- Drive the car for 10–15 miles to see if the light turns off on its own.
If the light remains on after a few days, move on to the next step.
Step 2: Read the Fault Codes
You can’t fix what you don’t understand. Use your OBD2 scanner to read the diagnostic trouble codes (DTCs) stored in the car’s computer.
- Locate the OBD2 port—on the E39 M5, it’s under the dashboard on the driver’s side, near the steering column.
- Plug in your OBD2 scanner and turn the ignition to the “ON” position (do not start the engine).
- Follow the scanner’s instructions to read the codes. Most devices will display codes like “P0171” or “P0420.”
- Write down all the codes and research what they mean. Free resources like OBD-Codes.com or BMW forums can help.
For example:
– P0171 = System too lean (Bank 1)
– P0300 = Random/multiple cylinder misfire
– P0420 = Catalyst system efficiency below threshold
Step 3: Diagnose and Repair the Issue
Once you know the code, it’s time to investigate. Here are a few common fixes:
- O2 Sensor Failure: If you see P0135 or P0141, the oxygen sensor may be faulty. These are located in the exhaust manifold and downpipe. Replacement is straightforward but may require lifting the car.
- MAF Sensor Issues: A dirty or failing MAF sensor (code P0101 or P0102) can cause poor performance. Clean it with MAF cleaner spray or replace it if necessary.
- Ignition Coils or Spark Plugs: Misfire codes (P0301–P0308) often point to bad coils or worn plugs. The E39 M5 has 8 coils—check each one for cracks or corrosion.
- Vacuum Leaks: Look for cracked hoses, especially around the intake manifold. Use a smoke machine or spray carb cleaner to find leaks (listen for RPM changes).
Always address the root cause before clearing the light. Clearing it without fixing the problem will only make it come back—and possibly worsen the issue.
Step 4: Clear the Service Engine Soon Light
After repairs are complete, it’s time to clear the codes.
- Reconnect your OBD2 scanner.
- Turn the ignition to “ON.”
- Navigate to the “Clear Codes” or “Erase DTCs” option on your scanner.
- Confirm the action. The scanner will reset the fault memory.
- Turn off the ignition and unplug the scanner.
The service engine soon light should now be off. If it comes back immediately, the problem wasn’t fully resolved.
Step 5: Test Drive and Monitor
Take your M5 for a 15–20 minute drive, including highway speeds if possible. This allows the car’s computer to run its self-tests and confirm that the issue is fixed.
If the light stays off, congratulations—you’ve successfully cleared the service engine soon light!
Alternative Methods (And Why They’re Not Recommended)
Some people try to clear the light by disconnecting the battery. While this may reset the computer temporarily, it’s not a reliable or safe method.
- Battery Disconnection: Disconnecting the negative terminal for 10–15 minutes can reset the ECU, but it also resets radio presets, clock, and adaptive settings. More importantly, it won’t clear all fault codes—especially on newer BMWs with advanced systems.
- Fuse Pulling: Removing the ECU fuse is risky and can cause electrical issues. Avoid this method.
- Manual Button Presses: Unlike maintenance lights, the service engine soon light cannot be reset using dashboard button combinations. Don’t waste your time trying.
Stick with the OBD2 scanner method for best results.
Troubleshooting Tips
Even with the right tools, things can go wrong. Here are some common issues and solutions:
- Scanner Won’t Connect: Check the OBD2 port for dirt or bent pins. Try a different scanner or cable.
- Codes Keep Returning: This means the problem isn’t fixed. Recheck your repairs or consult a BMW specialist.
- “No Communication” Error: Could indicate a faulty ECU, wiring issue, or blown fuse. Check fuse box under the hood (fuse 43 is often related to OBD2 power).
- Light Comes Back After Clearing: The fault is still active. Use your scanner to see if new codes appear.
When to See a Professional
While many E39 M5 owners enjoy DIY repairs, some issues require expert attention. Visit a BMW specialist if:
– You’re unable to read or clear codes
– The problem involves the transmission, ECU, or wiring harness
– You suspect a catalytic converter failure (common on high-mileage M5s)
– You’re uncomfortable working with electrical systems
A professional diagnostic can save time and prevent costly mistakes.
Conclusion
Clearing the service engine soon light on your E39 BMW M5 doesn’t have to be a mystery. With the right tools and a systematic approach, you can diagnose the issue, make the repair, and reset the light with confidence.
Remember: the light is your car’s way of saying, “Hey, something’s wrong.” Don’t ignore it. Always investigate the cause before clearing the code. A little effort now can prevent major repairs down the road.
Whether you’re tackling an O2 sensor replacement or just tightening a gas cap, taking care of your M5 ensures it continues to deliver the thrilling driving experience BMW is known for. Stay proactive, stay informed, and enjoy the ride.