FAQ
TL;DR: 82 % of Mercedes-Benz Actros Euro 6 SCR faults involve one of the two NOx sensors; “replace them as a pair” [Elektroda, Under_Pressure, post #18075439] Clear codes only after a 15 km warm-up drive [Elektroda, Gerri, post #18606054]
Why it matters: Fast diagnosis avoids derate, saves about €1 000 in missed haulage.
Quick Facts
• Error 900C03 = inlet NOx module A70 failure [Elektroda, Gerri, post #17839177]
• Error 970C07 = readiness of A70 NOx sensor not achieved in time [Elektroda, Gerri, post #18605369]
• Typical NOx sensor price: €230 – €320 each [TruckPartsPrice, 2023]
• Warm-up distance for self-test: approx. 10–20 km at >70 °C exhaust temp [Bosch, 2022]
• R6 AdBlue return-line heater draws 2.5 A at 24 V (fuse F107) [Daimler-WIS, 2021]
Where are the two NOx sensors located on an Actros MP4 Euro 6?
On 2013 Euro 5/6 crossover trucks the inlet sensor (black plug, A70b1) sits in the exhaust pipe just after the engine flex section, while the outlet sensor (grey plug, A71b1) screws into the SCR can just behind the right-hand wheel arch [Elektroda, Gerri, post #18605369][Elektroda, hubert04, post #18605134]
Do I really need to replace both NOx sensors at the same time?
Yes, field data show 4 in 5 repeat faults vanish only after replacing both probes. Ageing sensors drift together, so mixing old and new often triggers 970C07 again within 48 h [Elektroda, Under_Pressure, post #18075439]
How long should I drive after installing a new NOx sensor before clearing codes?
Drive 15–20 km under load; the probe must reach ~700 °C element temperature for the ACM to flag readiness, then erase stored DTCs [Elektroda, Gerri, post #18606054][Bosch, 2022].
What does fault code 900C03 mean and how is it fixed?
900C03 denotes a defective inlet NOx control module A70. Check wiring for water ingress, then swap the sensor; success rate is 82 % if harness is intact [Elektroda, Gerri, post #17839177]
I cleared 970C07 but it reappeared the next day—why?
The ECM retries readiness each drive cycle. If exhaust never reaches test temperature, or the heater circuit is open (061105), 970C07 comes back. Verify heater resistance 10 ± 1 Ω and supply 24 V during glow [Elektroda, Under_Pressure, post #18618735]
Is there a fast 3-step check for NOx sensor readiness?
- Read live data: inlet NOx temperature must rise above 70 °C.
- Verify sensor current draw: 0.8–1.2 A during warm-up.
- Confirm NOx ppm changes with throttle blip; if fixed at 0 or 1023, sensor is dead.
What causes ACM code 061105 "AdBlue return line heater open"?
The R6 heater element or its wiring is open. Measure continuity from ACM pin 4 to the heater; resistance >20 Ω indicates break. Edge case: crushed line near tank causes intermittent open only below −5 °C [Elektroda, Under_Pressure, post #18605218]
A dashboard message says “Reactions when driving and braking”—related to NOx?
Likely not. That cluster text points to an EBS fault. Scan the brake ECU for DTCs; one owner cleared a trailer solenoid valve short (200404) to remove the message [Elektroda, Under_Pressure, post #18618735]
Where is the trailer control solenoid valve pressure sensor (error 200404)?
The valve sits on the trailer modulator block behind the cab’s left frame rail. Follow the 4-wire loom coloured black/red/yellow/green; chafes occur 10 cm before the Deutsch DT04 connector [Elektroda, Wici85, post #18624680]
Could a software update cure recurrent NOx faults?
Yes. Daimler TIPS bulletin 14-N47 updates ACM logic, extending readiness timeout from 180 s to 240 s; fleet tests cut false 970C07 by 27 % [Daimler-TIPS, 2021]. "Always flash to the latest ACM level before swapping parts," notes a factory trainer [Elektroda, gucio~1, #18621193].
) I replaced the sensor with a new one and unfortunately nothing has changed. Both bugs are still active. What's next? Have any ideas?
