Hello fellow car enthusiasts and Mercedes experts,
I’m reaching out to this community in hopes of finding some guidance on a frustrating “no crank/no start” problem I’m experiencing with my 2007 Mercedes CLK 350. I purchased the vehicle in non-operable condition, and I’ve been diligently working to diagnose and rectify the issue for over a month now, but haven’t yet cracked the code. I’ve thoroughly researched numerous online resources and threads discussing similar “no crank” scenarios, and I’ve diligently followed the suggested troubleshooting steps, yet my CLK 350 remains stubbornly immobile.
To provide a concise overview: the car is not cranking or starting. Vehicle authorization seems to be functioning correctly. The ECU (Engine Control Unit) has been tested on a vehicle simulator and appears to be in good working order. I initially encountered an error code related to the generator, and currently, I’m observing a lack of ground at the starter relay. Furthermore, there is no spark at the spark plugs and no fuel delivery to the engine. Despite these issues, I can hear the fuel pump engaging when attempting to start the car.
Let me elaborate on the steps I have taken in more detail:
The saga began with a completely dead battery (registering 0V). The first step was to replace it with a brand new battery. After installing the new battery, I connected an OBD scanner to check for any stored error codes. Initially, two errors were present:
- B112E IC (Instrument Cluster): “Control unit is faulty (ROM: read error).”
- 1337 ECM (Engine Control Module): “Alternator serial interface (current and stored).”
The instrument cluster display was indeed exhibiting erratic behavior, so I opted to acquire a used instrument cluster. To ensure compatibility and retain vehicle-specific data, I utilized an eBay service to transfer the memory from my original cluster to the replacement unit. This intervention successfully resolved the B112E IC error.
While the instrument cluster was undergoing repair, I removed the alternator and took it to a specialized starter/alternator service for testing. They assessed the alternator and reported that it was in excellent condition, functioning as expected, essentially “like new.” This was somewhat surprising given the persistent alternator error code.
Moving to the starting system, I checked the voltage at the starter relay, and the +12V supply appears to be present and correct. However, I discovered a critical issue: the starter relay is not receiving a ground signal. According to the Mercedes-Benz wiring diagrams, the ground signal for the starter relay originates from the ECU. This finding led me to suspect a potential fault within the ECU itself.
Consequently, I sent the ECU to an ECU repair service that advertised vehicle simulator testing. They performed comprehensive tests on my ECU using a vehicle simulator, and their report indicated that the ECU was functioning without any errors. This result was unexpected and somewhat contradictory to my initial suspicion.
Currently, the vehicle’s authorization system appears to be functioning correctly. I’ve verified the status of the EZS (Electronic Ignition Switch) and ESL (Electronic Steering Lock), and both are reporting “YES” for authorization. The transmission module also indicates “OK” when the gear selector is in the “Park” position. Furthermore, the instrument cluster confirms drive authorization is active. I used a diagnostic procedure similar to what’s shown in online videos to assess these systems.
To rule out potential wiring issues, I meticulously checked the wiring harness from the starter relay to the ECU and from the alternator to the ECU. I also thoroughly inspected all relevant fuses and relays located in the front SAM (Signal Acquisition Module), the fuse box to the left of the steering wheel, and the fuse box in the trunk. As a further diagnostic step to isolate any potentially faulty modules interfering with the CAN bus system, I systematically removed fuses for non-essential systems, leaving only the engine-related fuses in place.
In my online research, I encountered a case where a “no ground” issue at the starter relay was resolved by implementing a workaround: adding a manual ground wire to the starter relay. To test this, I connected a wire directly from a known ground point to the ground pin of the starter relay. With this modification, the engine now cranks when the ignition key is turned! However, despite cranking, the engine still fails to start.
Further investigation revealed a lack of both spark and fuel delivery. I removed a spark plug, grounded it to the engine block, and cranked the engine, but observed no spark. The spark plug itself remained dry, indicating no fuel delivery to the cylinder. Despite the lack of fuel delivery to the engine, I can clearly hear the fuel pump operating when I attempt to start the car, and the OBD scanner confirms that the fuel pump is indeed running.
I’m still puzzled by the persistent alternator error code despite the alternator testing as good. Could this be a related issue or a red herring?
At this point, I’m reaching the limits of my diagnostic capabilities and knowledge. I’m hesitant to conclude that the crank position sensor is faulty because the OBD scanner registers engine speed (approximately 120 RPM) while cranking, suggesting the sensor is at least partially functional.
I am now seeking expert advice and suggestions from anyone who may have encountered a similar “no crank no start” situation with a 2007 Mercedes CLK 350 or possesses in-depth knowledge of these systems. What further diagnostic steps should I undertake? Are there any specific components or systems I should focus on based on the symptoms I’ve described? Any insights or recommendations would be greatly appreciated as I continue to troubleshoot this perplexing issue.
