Mercedes-Benz U0109: Lost Communication With Fuel Pump

Make: Mercedes-Benz
Code: U0109
System: Network / communication (CAN)
Severity: Warning

In short

Mercedes-Benz U0109 = Lost Communication With Fuel Pump Control Module. This code is defined for Mercedes-Benz.
CarCoding classifies this code as warning 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 U0109 mean?

The control unit stores a standard fault code when a measurement falls outside its expected range. U0109 corresponds to Lost Communication With Fuel Pump Control Module.

U0109 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 U0109.

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 U0109:

Fuel pump module failure
CAN bus
Wiring

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 U0109; 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 U0109 as warning severity: it is not in the group that requires stopping immediately, but the fault will not clear itself. If you notice changed driving behaviour, loss of power, higher consumption or unusual noise, bring the diagnosis forward.

A stored code can also affect the emissions readiness monitors and the outcome of a roadworthiness test. How your vehicle behaves right now matters more than this general classification: if there is a red warning on the dashboard, do not keep driving.

Other Mercedes-Benz fault codes

Other manufacturer-specific codes for the same make:

All Mercedes-Benz fault codes →

Read Mercedes-Benz U0109 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 U0109 mean?

Mercedes-Benz U0109 means “Lost Communication With Fuel Pump Control Module”. In the CarCoding database it sits in the Network / communication (CAN) group with warning 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 U0109?

The CarCoding database lists the following possible causes for Mercedes-Benz U0109: Fuel pump module failure; CAN bus; Wiring. This list is not a diagnostic order; measurement decides which one applies.

Can you drive with fault code Mercedes-Benz U0109?

Mercedes-Benz U0109 is in the warning severity class: it is not in the group that requires stopping immediately, but the fault will not clear itself. If you notice changed driving behaviour, loss of power or higher consumption, bring the diagnosis forward. Base the decision on how the vehicle behaves right now and on the freeze frame data.

Will clearing Mercedes-Benz U0109 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.

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.