FAQ
TL;DR: For Actros MP4 Euro 6 ACM fault loops, start with 1 controller software check/update; "a software update in the controller was needed." Authorized online service applies patches automatically; clone SD tools lack update access. Clear faults after updating and validate regeneration. [Elektroda, Gerri, post #18952130]
Why it matters: This FAQ helps Actros MP4 Euro 6 owners and techs fix recurring ACM codes tied to DPF events.
Quick Facts
- First-line diagnosis: run the OEM dynamic test for the second error in Star Diagnose. [Elektroda, Gerri, post #18950918]
- SD clone units can run the dynamic test offline; no network login required. [Elektroda, Gerri, post #18951628]
- “External data carrier” prompt = no online contact; some emissions faults need this procedure to clear. [Elektroda, Gerri, post #18951866]
- Dealer sessions apply controller software updates automatically; clone tools do not get patch access. [Elektroda, Gerri, post #18952130]
- Edge case: 900C0B returned after two NOx swaps; regen ran nonstop and fuel use spiked. [Elektroda, atego.l, post #19847087]
What do ACM codes 970C07 and 900C0B mean on an Actros MP4 Euro 6?
970C07 flags that sensor readiness conditions were not ensured in time. 900C0B reports an incorrect A70 b1 signal at the catalyst inlet. In one case, faults cleared, then returned when DPF regeneration fired again. Replacing the pre-catalyst sensor alone did not end the cycle. Plan OEM-guided diagnosis next. [Elektroda, Cobra1609, post #18950372]
How do I start diagnosing 900C0B?
Start with the dynamic test in the original Star Diagnose. It correlates sensor values under load. "And that's where I would start." Confirm conditions, then assess A70 b1 signal plausibility. Complete the test before replacing parts. [Elektroda, Gerri, post #18950918]
Can I run the Star Diagnose dynamic test without logging in?
Yes. "The test itself should fly even on an SD clone." You do not need network login to execute the dynamic test. Use a stable power supply and follow on-screen conditions. This only runs the test; it does not apply software updates. [Elektroda, Gerri, post #18951628]
Why is Star Diagnose asking for an “external data carrier”?
That prompt appears when there is no online connection. The tool prepares a data file for Mercedes to process and return. Some emissions faults require this procedure to clear. The manufacturer tracks vehicles that might pollute due to faults. Prepare the file or connect online to continue. [Elektroda, Gerri, post #18951866]
Do I need a dealer visit for a controller software update?
Often yes. The system may require a software update to repair the fault. With online authorized service, the process is automatic. Independent tools cannot access those patches. Schedule the update if diagnostics point to software. [Elektroda, Gerri, post #18952130]
Will a clone SD tool apply ACM “patches” or updates?
No. Clones of the original service computer do not have access to program updates provided as patches. They can run tests, read codes, and guide diagnosis. Use them to confirm faults, then plan an authorized update if required. [Elektroda, Gerri, post #18952130]
My 900C0B returns after each DPF regeneration and fuel use is excessive—what does that suggest?
Users report this loop even after replacing multiple NOx sensors. One case used two NOx sensors, yet 900C0B persisted. Regeneration ran continuously, and fuel consumption spiked. This points beyond a failed sensor. Document the pattern and continue structured diagnostics. [Elektroda, atego.l, post #19847087]
I replaced the upstream sensor, but the fault returned two weeks later—what next?
One report saw 900C0B return about two weeks after replacement. The pre-catalyst sensor was new, yet faults reappeared on regeneration. That suggests the root cause remained unresolved. Proceed with deeper diagnosis and verify upstream signals. [Elektroda, Cobra1609, post #18950372]
Is an online connection sometimes required to clear emissions faults?
Yes. Some ecology-related errors need the data file procedure or live online contact to clear. The system enforces this to manage environmental compliance. Offline, you will see the data carrier prompt. Prepare and submit the file to continue. [Elektroda, Gerri, post #18951866]
Can you remotely verify if my ACM software is current?
No. Remote helpers cannot check your controller’s software version status from afar. Without database access, no one can confirm update currency. Only an authorized session can verify and apply patches automatically. Ask the dealer to check your VIN against available updates. [Elektroda, Gerri, post #18952130]
How do I run the Star Diagnose dynamic test for ACM?
- Open Star Diagnose, select the vehicle, and enter ACM.
- Choose the dynamic test for the active fault and follow prompts.
- Save results, clear codes, road test, then recheck.
"The second error is a corresponding dynamic test in the original diagnostic computer." [Elektroda, Gerri, post #18950918]
Should I try the test first or go straight to the dealership?
Run the dynamic test yourself first. If it passes and indicates software, plan a dealer update. "Then, possibly, you will go to the software update to the Dealership." That sequence confirms the root cause before parts replacement. [Elektroda, Gerri, post #18953768]
