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fault in communication with vehicle ecu

AL Ansari Automobile
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fault in communication with vehicle ecu in car






Communication Between the ECM and Other Modules – Causes, Symptoms, Diagnosis, and Repair Guide

What Does "Communication Between the ECM and Other Modules" Mean?

Modern vehicles contain multiple electronic control units (ECUs) that communicate with each other through a network called the CAN Bus (Controller Area Network).

The Engine Control Module (ECM), also known as the Engine Control Unit (ECU), acts as one of the most important controllers in the vehicle. It continuously exchanges information with other modules such as:

  • Transmission Control Module (TCM)

  • ABS Module

  • Airbag Module (SRS)

  • Body Control Module (BCM)

  • Instrument Cluster

  • Immobilizer Module

  • Steering Control Module

  • TPMS Module

  • HVAC Module

  • Power Steering Module

When communication between the ECM and these modules is interrupted, the vehicle may store communication fault codes and display warning messages.

Common Communication Error Codes

Different manufacturers use different fault codes, including:

Generic U-Codes

  • U0100 – Lost Communication with ECM/PCM

  • U0101 – Lost Communication with TCM

  • U0121 – Lost Communication with ABS Module

  • U0140 – Lost Communication with BCM

  • U0155 – Lost Communication with Instrument Cluster

Manufacturer-Specific Codes

  • BMW A0B4 Communication Fault

  • Mercedes U-Codes

  • Volkswagen CAN Bus Errors

  • Hyundai Communication DTCs

  • Toyota Network Communication Faults

Vehicles Commonly Affected

Communication faults can occur in almost all modern vehicles:

BMW

  • E90

  • E60

  • E70

  • F10

  • F30

Mercedes-Benz

  • C-Class

  • E-Class

  • S-Class

  • ML-Class

Audi & Volkswagen

  • A4

  • A6

  • Q5

  • Golf

  • Jetta

  • Passat

Toyota

  • Corolla

  • Camry

  • Fortuner

  • Innova

Hyundai & Kia

  • i20

  • Creta

  • Verna

  • Venue

  • Seltos

Maruti Suzuki

  • Swift

  • Dzire

  • Baleno

  • Brezza

Tata Motors

  • Nexon

  • Harrier

  • Safari

  • Tiago

Mahindra

  • XUV500

  • Scorpio

  • Thar

  • XUV700

Symptoms of ECM Communication Failure

When the ECM loses communication with other modules, several symptoms may appear.

Check Engine Light ON

The engine warning lamp may illuminate.

ABS Warning Light

ABS and traction control systems may stop working.

Airbag Warning Light

The SRS system may become disabled.

Vehicle Will Not Start

Immobilizer communication may fail.

No Communication with Scanner

Diagnostic tools may be unable to communicate with the ECM.

Transmission Problems

Automatic transmission may enter limp mode.

Power Steering Warning

Electronic steering systems may stop functioning.

Multiple Warning Lights

Several dashboard lights may appear simultaneously.

Main Causes of ECM Communication Failure

1. ECM Failure

A damaged ECM is one of the most serious causes.

Common ECM failures include:

  • Internal circuit damage

  • Water damage

  • Burned components

  • Processor failure

  • EEPROM corruption

When the ECM fails, communication with all modules may stop.

2. Blown Fuse

Many communication faults are caused by a simple fuse problem.

If the ECM fuse blows:

  • ECM loses power

  • Communication stops

  • Vehicle may not start

Always inspect:

  • ECM Fuse

  • IGN Fuse

  • Main Relay Fuse

before replacing expensive components.

3. Water Damage

Water entering the ECM connector is a common cause.

Water can cause:

  • Corrosion

  • Short circuits

  • Pin damage

  • Communication interruption

Common water entry locations:

  • Windshield leaks

  • Flood-damaged vehicles

  • Engine washing

  • Blocked drain channels

4. Damaged ECM Socket or Connector

A damaged connector can interrupt communication.

Possible issues include:

  • Bent pins

  • Broken terminals

  • Corroded terminals

  • Loose connectors

Even a single damaged CAN wire can stop communication.

5. CAN Bus Wiring Problems

The CAN Bus network consists of:

  • CAN High Wire

  • CAN Low Wire

If either wire becomes damaged:

  • Open circuit

  • Short to ground

  • Short to power

  • Wire breakage

communication between modules may fail.

6. Weak Battery Voltage

Low battery voltage can cause temporary communication failures.

Common situations include:

  • Weak battery

  • Dead battery

  • Long vehicle storage

  • Poor charging system

Many modules stop communicating below safe operating voltage.

7. Poor Ground Connections

Ground faults are often overlooked.

Symptoms include:

  • Intermittent communication

  • Random warning lights

  • Module reset issues

Always inspect:

  • Engine grounds

  • Chassis grounds

  • ECM grounds

8. Aftermarket Accessories

Poorly installed accessories can interfere with the CAN Bus network.

Examples:

  • GPS Trackers

  • Aftermarket Alarms

  • Remote Starters

  • Multimedia Systems

Incorrect wiring can disrupt module communication.

How to Diagnose ECM Communication Problems

Step 1 – Scan All Modules

Use a professional scanner:

  • Launch X431

  • Autel MaxiSys

  • Xtool

  • Bosch KTS

Check which modules communicate and which do not.

Step 2 – Check Battery Voltage

Normal battery voltage:

  • Engine OFF: 12.4V–12.8V

  • Engine Running: 13.5V–14.8V

Low voltage can trigger communication faults.

Step 3 – Check Fuses

Inspect all:

  • ECM Fuses

  • BCM Fuses

  • Ignition Fuses

  • CAN Network Fuses

Step 4 – Inspect ECM Connector

Look for:

  • Water

  • Corrosion

  • Loose terminals

  • Burn marks

Step 5 – Test CAN Bus Network

Measure CAN voltage and resistance.

Typical CAN resistance:

Approximately 60 Ohms with ignition OFF.

Abnormal readings indicate wiring issues.

Step 6 – Verify Power and Ground

Confirm:

  • Battery Power

  • Ignition Power

  • Ground Supply

at the ECM connector.

Preventing ECM Communication Problems

To avoid expensive repairs:

✔ Keep battery in good condition.

✔ Avoid pressure washing near ECM connectors.

✔ Repair windshield leaks immediately.

✔ Use genuine fuses.

✔ Inspect grounds regularly.

✔ Avoid poor-quality aftermarket wiring.

✔ Perform professional diagnostics before replacing modules.

✔ Protect electrical connectors from moisture.

Repair Cost

Fuse Replacement

₹50 – ₹500

Wiring Repair

₹1,000 – ₹10,000

Connector Repair

₹2,000 – ₹15,000

ECM Repair

₹5,000 – ₹30,000

ECM Replacement

₹15,000 – ₹150,000+

depending on vehicle make and model.

Final Conclusion

Communication between the ECM and other vehicle modules is essential for the proper operation of modern vehicles. When communication fails, multiple systems such as the engine, transmission, ABS, airbags, and immobilizer may stop functioning correctly. Common causes include blown fuses, damaged wiring, water intrusion, poor grounds, low battery voltage, connector corrosion, and ECM failure. Proper diagnosis should always begin with checking power supply, fuses, wiring, and CAN Bus integrity before replacing expensive control modules. Early detection and preventive maintenance can save significant repair costs and prevent complete vehicle breakdowns.










Fault in communication with vehicle (ECU)


(ECM) ( PCM)

 In this case  cars problem starting issue

sometimes starting trouble  engine cranking  

but car not starting  Any vehicle of not 

communication with scanner showing this 

error fault  first check junction box fuse ECU 

engine control module  check ignition fuse 

main relay fuse ECU fuse and on car 

dashboard cluster metre check engine light 

showing or not

Fault in communication ECU



Possible solutions of the error


Check fuse and relay  ECM engine control 

module wiring  socket and connector chain 

wiring can communication low and high can 

line  if  ok fault in ECM engine control module







fault in communication with vehicle ecu















fault in communication with vehicle ecu



vehicle ecu fault in communication














Agar koi bhi Cars mein is type ka error 

scanning karne ke bad Aata Hai tu sabse pahle 

a kar mein jo problem sakte hain se 

sometimes Kar start hoti hai hi aur Kabhi 

Nahin Hoti Hai Tu sabse pahle a dashboard 

metre ke andar check karna chahie check 

engine light a Rahi Hai Ki Nahin is cash mein 

check engine light bhi nahin aata hai 

sometimes sabse pahle iska fuse check karna 

chahie Uske bad main relay ECM car engine 

control module Uske bad CM ka socket aur 

connector Agar yah sab ok hai hi to isliye main 

fault ho sakta hai






communication between the ecm and the other module
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