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DTC codes / BMW codes / P1609

P1609 · BMWSerial Communicating Link EML

P1609 on BMW vehicles indicates a communication failure on the serial data link between the engine control module (DME) and the electronic throttle control module, known as EML (Elektronische Motorleistungsregelung). The DME has detected that it cannot reliably exchange messages with the EML over the dedicated serial line, which is critical for coordinating throttle valve position with engine torque requests.

SystemPowertrain
Code typeBMW specific
SeverityMedium
Fix difficultyProfessional
AreaComputer and output circuits

Symptoms you may notice

  • Illuminated check engine light with possible EML or DSC warning lamps on the instrument cluster
  • Reduced engine power or limp mode, often limiting throttle response to a fixed low percentage
  • Erratic or delayed throttle response, with the engine sometimes idling higher than normal
  • Intermittent stalling or difficulty starting if the communication loss is severe
  • Often no symptoms besides the warning light if the fault is stored but the link still functions intermittently

Common causes, most likely first

  1. Damaged, chafed, or corroded wiring in the serial link between the DME and EML modules
  2. Loose or contaminated connector pins at either the DME or EML harness plug
  3. Failed EML control module, often due to internal circuit board faults or water intrusion
  4. Failed DME control module, particularly a faulty serial communication driver inside the unit
  5. Voltage supply or ground issue affecting the EML module, causing it to drop offline intermittently
  6. Electromagnetic interference from aftermarket electronics or poor grounding points along the harness

How to diagnose and fix it

  1. Clear the fault code and perform a road test to confirm whether P1609 returns as current or remains stored
  2. Visually inspect the serial link wiring between the DME and EML for chafing, corrosion, or loose pins, and repair as needed
  3. Measure resistance and continuity on the serial communication line with a multimeter to rule out an open or shorted conductor
  4. Check the EML module's power and ground supplies under load to confirm stable voltage during cranking and running
  5. Substitute a known-good EML module and recheck communication to isolate whether the EML or DME is at fault
  6. If the DME is suspected, perform a module swap with a matched unit and verify the serial link restores communication
  7. After repair, clear all fault memory and complete a throttle adaptation reset using a BMW-capable scan tool

What BMW Technicians Check Before Swapping Modules

  • A stored P1609 often appears alongside throttle-related codes such as P0120 or P0222, and technicians who replace the throttle body first miss the actual serial link fault.
  • Water intrusion into the EML connector or the DME housing is a common cause on older BMW models, so always inspect for corrosion before condemning a module.
  • Aftermarket alarm or audio installations that tap into the CAN or serial wiring can introduce interference that sets P1609 intermittently, so check for non-factory wiring first.
  • The serial link between DME and EML is a dedicated line, not the CAN bus, so a generic OBD-II scan tool may not show live EML data even when the fault is active.
  • A weak battery or failing alternator can cause the EML module to drop offline momentarily, setting P1609 without any permanent wiring fault.

Can I keep driving with P1609?

You can usually drive the vehicle to a workshop if the engine runs and throttle response is not severely limited, but avoid heavy acceleration or high-speed driving because limp mode may engage without warning. If the engine stalls or throttle response becomes unpredictable, stop driving and arrange a tow.

Tools that help

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Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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