Mercedes-Benz U0100: Lost CAN-C Communication With ECM

Make: Mercedes-Benz
Code: U0100
System: Network / communication (CAN)
Severity: Critical

In short

Mercedes-Benz U0100 = Lost CAN-C Communication With ECM. This code is defined for Mercedes-Benz.
CarCoding classifies this code as critical severity under network / communication (can).
The database lists 3 possible causes; freeze frame and live data decide which one applies — work by measuring, not by replacing parts.

What does Mercedes-Benz U0100 mean?

The control unit stores a standard fault code when a measurement falls outside its expected range. U0100 corresponds to Lost CAN-C Communication With ECM.

U0100 sits in the code range standardised by SAE/ISO, because its second digit is 0. This page shows what the code means on the Mercedes-Benz side and the possible causes the CarCoding database holds for Mercedes-Benz.

For the make-independent standard definition: fault code U0100.

CarCoding files this code under Network / communication (CAN). Codes starting with U describe a silence rather than a fault: one module did not receive a message it expected from another. That does not mean the other module is broken. Standard codes in this group →

All Mercedes-Benz fault codes →

Vehicles supported in CarCoding: Mercedes-Benz models.

Possible causes

Possible causes the CarCoding database holds for Mercedes-Benz U0100:

CAN-C bus fault
ECM power loss
Wiring damage

The order is not a probability ranking or a diagnostic sequence. The same code can have different causes on different vehicles, so treat the list as a starting set to be narrowed down by measurement.

How is it diagnosed?

The sequence below is not specific to U0100; it applies to OBD-II fault code diagnosis in general. These are the steps that are most often skipped:

Read all the codes together. A single code is rarely the whole story; the other codes stored at the same time often point to the real cause.
Read the freeze frame. The rpm, engine load, coolant temperature and speed at the moment the code was stored tell you under what conditions the fault occurred. It is the single most valuable piece of data you have.
Identify which list the code is in. Confirmed (Mode 03), pending (Mode 07) and permanent (Mode 0A) codes are not the same thing. A code that appears only in the pending list means the fault has not been confirmed yet — most likely it is intermittent.
Look at live data. Deliberately recreate the condition from the freeze frame and watch the relevant sensor values in real time. If you can reproduce the fault, you no longer have to guess.
Clear and verify. After fixing the fault, clear the code (Mode 04), take a verification drive similar to the freeze frame conditions and read the pending codes again. An empty list means the fault is really gone.

The cost of clearing codes: Clearing also resets the emissions readiness monitors. Until those monitors return to “complete”, the vehicle may not pass an emissions test. So read and record the codes before clearing them.

Can you keep driving?

CarCoding classifies Mercedes-Benz U0100 as critical severity. The critical class means the code belongs to a group that should not be ignored; how urgent it is on your vehicle is decided by the dashboard warnings, the way the car behaves and the freeze frame data.

Do not keep driving: If the check engine light is flashing, if there is a red warning on the dashboard, or if the vehicle has lost power, is overheating or shows unusual noise or smell, stop somewhere safe and contact a qualified workshop. In the OBD-II standard a flashing check engine light means “a fault capable of causing damage is happening right now”.

Same code, different meaning on another make

The number U0100 is not used by Mercedes-Benz alone. On the makes below it indicates a different fault — which is exactly why interpreting a code without knowing the make is misleading:

Other Mercedes-Benz fault codes

Other manufacturer-specific codes for the same make:

All Mercedes-Benz fault codes →

Read Mercedes-Benz U0100 on your own vehicle

With an ELM327-based BLE OBD2 adapter, CarCoding reads confirmed, pending and permanent fault codes separately, pulls the freeze frame and explains every code in plain language. Clearing codes is done from the app as well. The app is free to download.

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Some advanced features require an in-app purchase.

Frequently asked questions

What does Mercedes-Benz fault code U0100 mean?

Mercedes-Benz U0100 means “Lost CAN-C Communication With ECM”. In the CarCoding database it sits in the Network / communication (CAN) group with critical severity. This code is in the standard OBD-II range, but what is shown here is its meaning on the Mercedes-Benz side.

What are the possible causes of Mercedes-Benz U0100?

The CarCoding database lists the following possible causes for Mercedes-Benz U0100: CAN-C bus fault; ECM power loss; Wiring damage. This list is not a diagnostic order; measurement decides which one applies.

Can you drive with fault code Mercedes-Benz U0100?

Mercedes-Benz U0100 is in the critical severity class and should not be ignored. If the check engine light is flashing, if there is a red warning on the dashboard, or if the vehicle has lost power, is overheating or shows unusual noise or smell, do not keep driving; stop somewhere safe and contact a qualified workshop.

Will clearing Mercedes-Benz U0100 fix it?

Clearing a code (OBD-II Mode 04) only resets the record in the control unit and the warning lamp; if the fault is still present the code returns once the verification cycle completes. Clearing also resets the emissions readiness monitors, so clearing codes before an emissions test can cause the vehicle to fail. The right order is: record the code and the freeze frame, fix the fault, clear the code, take a verification drive and read the pending codes again.

Does U0100 mean the same thing on every make?

No. In the CarCoding database the number U0100 has different meanings on these makes: BMW — Lost CAN Communication With DME; VAG — Lost CAN Communication With ECM. That is why you must know the vehicle make when interpreting a fault code.

Data source: the CarCoding fault code database. Code definitions follow the SAE J2012 standard; manufacturers may use different wording for their own codes. Everything on this page is generated from the code-specific database records.

Disclaimer: This page offers general diagnostic guidance and does not replace an inspection by a qualified workshop. Any work carried out on the vehicle is your own responsibility.