Engine Check Light Was On: Diagnosing Misfire in Mercedes-Benz ML 63 AMG (M157 Engine)
Engine check light was on and the owner of a Mercedes-Benz ML63 AMG knew something wasn’t right. When that warning light appears on the dashboard, it’s your engine’s way of calling for help. In this high performance SUV equipped with the powerful M157 engine, even minor faults can lead to serious performance issues.
This case study explores how a simple warning led to the discovery of a cylinder misfire and a faulty ignition coil. Using expert diagnostics, we identified the root cause, replaced the necessary components, and restored smooth engine performance. If your check engine light comes on, don’t ignore it, it might be signaling more than just a minor glitch.
Initial Diagnostics: Quick Test and Fault Code Review
As the first step, a full system scan was performed using the XENTRY diagnostic tool. The following fault codes were retrieved:
- P035149 : The actuation of ignition coil 1 has an electrical fault or open circuit. There is an internal electrical fault
- P035196 : The actuation of ignition coil 1 has an electrical fault or open circuit. There is an internal component fault
- P030085 : Combustion misfiring has been detected. There is a signal above the permissible limit value.
- P030185 : Combustion misfiring of cylinder 1 has been detected. There Is a signal above the pernussible limd value.
These faults confirmed that the engine check light was on due to repeated misfires in cylinder 1, likely caused by a failing ignition coil or spark plug.
Step-by-Step Inspection
To resolve the issue, we followed a structured diagnostic approach:
- Spark Plug Inspection
- Checked the spark plug in cylinder 1 for fouling, wear, and improper gap.
- Found excessive wear and carbon deposits, indicating poor combustion.
- Ignition Coil Testing
- The coil was tested for continuity and resistance.
- Found an internal electrical fault confirming code P035149 and P035196.
- Injector Actuation Test
- Performed injector function test to rule out fueling issues.
- Injector response was normal.
- Wiring Harness Inspection
- Carefully examined the wiring and connector for ignition coil 1.
- No signs of corrosion or open circuit were found.
Fault Counter Check and Component Replacement
With the fault counter increasing consistently during testing, it was clear that Ignition Coil 1 and the Spark Plug were faulty and needed to be replaced. New OEM parts were installed to ensure optimal performance.
Final Outcome: Smooth Running Restored
After replacement, a test drive was conducted under various load conditions. The engine ran smoothly, and the engine check light was off. Fault memory was cleared and did not return, confirming the issue was fully resolved.
Conclusion: Why the Engine Check Light Was On
In this case, the engine check light was on because of a faulty ignition coil and worn spark plug in cylinder 1—a common cause of misfiring in high-performance engines like the M157. Proper diagnostics, component testing, and replacement resolved the issue and restored the ML 63 AMG to peak performance.
Can a bad ignition coil cause the check engine light to come on?
Yes, a bad ignition coil is one of the most common reasons the engine check light comes on, especially in high-performance engines like the Mercedes M157 found in the ML63 AMG. The ignition coil is responsible for delivering voltage to the spark plugs.
If it fails, the combustion process in the cylinder becomes erratic, leading the engine control unit (ECU) to detect misfiring and log fault codes like P0351 or P0301. These faults trigger the check engine light to warn the driver of a serious ignition issue.
Timely replacement of the faulty coil is crucial, as continued driving can cause unburned fuel to damage the catalytic converter and reduce engine efficiency.
What are the symptoms of a bad ignition coil in a Mercedes?
When an ignition coil starts to fail in a Mercedes especially in models like the ML63 AMG—you’ll often notice symptoms such as rough idling, hesitation during acceleration, reduced engine power, and poor fuel economy.
In many cases, the vehicle may also vibrate or shake during idle or under load. One of the most obvious signs is the engine check light coming on, frequently due to stored misfire fault codes.
You might also detect a fuel smell from the exhaust, indicating incomplete combustion. If left unresolved, this condition can lead to damage to the catalytic converter or internal engine components.
It’s important to inspect the ignition coil and spark plug promptly if any of these symptoms appear.
Is it safe to drive with the check engine light on and misfire?
Driving with the check engine light on and a misfire is not considered safe, particularly in high-output engines like the Mercedes M157. A misfire means the air-fuel mixture in one or more cylinders isn’t being properly ignited.
This causes unburned fuel to enter the exhaust, which can overheat and damage the catalytic converter an expensive component to replace. It may also lead to engine knocking or power loss, especially when accelerating or climbing hills.
In some cases, it can trigger limp mode to protect the engine. If the light is blinking or you’re experiencing power loss or vibrations, stop driving and get the vehicle diagnosed immediately. Prompt repair will protect both performance and long-term engine health.
How do you fix a cylinder misfire on a Mercedes ML63 AMG?
To fix a cylinder misfire on a Mercedes ML63 AMG equipped with the M157 engine, you should begin with a complete diagnostic scan using a professional tool like XENTRY. Misfire-related codes such as P0301 (Cylinder 1 misfire) or P0351 (Ignition Coil 1 fault) often indicate issues with ignition components.
Start by checking the condition and gap of the spark plug in the affected cylinder, then test the ignition coil for internal faults. It’s also crucial to inspect wiring harnesses and perform an injector actuation test to rule out fuel delivery problems.
Once the faulty component typically a coil or plug is replaced, clear the fault memory and perform a road test to ensure smooth engine operation and verify the issue is resolved.
