U0100
High SeverityLost Communication with ECM/PCM
Network/Communication System
U0100 — Instant Answer
Lost Communication with ECM/PCM
Severity: HIGH SEVERITY
Meaning: A module has lost CAN bus communication with the engine control module.
Safe to drive? NO if CEL is flashing. YES with caution if solid, but repair this week.
Estimated repair cost: $0 - $800
Most common causes:
- 1. CAN bus wiring issue (35-45% of cases)
- 2. Faulty ECM (10-25% of cases)
- 3. Blown ECM fuse (10-25% of cases)
- 4. Corroded connector (10-25% of cases)
Symptoms
- ⚠️Multiple warning lights
- ⚠️No start
- ⚠️Various systems not working
- ⚠️Scan tool cannot connect to ECM
Related Symptoms
Common Causes
How to Diagnose U0100
- 1Check ECM fuses
- 2Check CAN bus wiring
- 3Inspect ECM connectors
- 4Test CAN bus communication
OEM Procedures for U0100
U0100 affects the Engine Control Module. Found 146 OEM service manual procedures.
12 90 120 Removing and installing/replacing control unit bracket (Cooper 4-door hatchback, Cooper 2-door hatchback, 2020-2023) - Replacement: Remount DME control unit and the integrated supply module (PDM)
12 90 120 Removing and installing/replacing control unit bracket (Cooper 4-door hatchback, Cooper 2-door hatchback, 2020-2023) - Replacement: Remount DME control unit and the integrated supply module (PDM)
12 90 120 Removing and installing/replacing control unit bracket (Cooper 4-door hatchback, Cooper 2-door hatchback, 2020-2023) - Replacement: Remount DME control unit and the integrated supply module (PDM)
12 90 120 Removing and installing/replacing control unit bracket (Cooper 4-door hatchback, Cooper 2-door hatchback, 2020-2023) - Replacement: Remount DME control unit and the integrated supply module (PDM)
12 90 120 Removing and installing/replacing control unit bracket (Cooper 4-door hatchback, Cooper 2-door hatchback, 2020-2023) - Replacement: Remount DME control unit and the integrated supply module (PDM)
12 90 120 Removing and installing/replacing control unit bracket (Cooper 4-door hatchback, Cooper 2-door hatchback, 2020-2023) - Replacement: Remount DME control unit and the integrated supply module (PDM)
12 90 120 Removing and installing/replacing control unit bracket (Cooper 4-door hatchback, Cooper 2-door hatchback, 2020-2023) - Replacement: Remount DME control unit and the integrated supply module (PDM)
12 90 120 Removing and installing/replacing control unit bracket (Cooper 4-door hatchback, Cooper 2-door hatchback, 2020-2023) - Replacement: Remount DME control unit and the integrated supply module (PDM)
Showing 8 of 146 procedures
OEM Diagnostic Flowchart
Scroll to load technician if/then branches.
U0100 requires a scanner that reads network modules — basic code readers won't see it.
ArtiLink600
$99
DIYers working on ABS/airbag systems
View on TOPDON
ArtiDiag900 Lite
$299.24
Serious DIYers and side-hustle mechanics
View on TOPDONGot a repair estimate for U0100? Check if the quote is fair before ordering parts.
Parts & Tools for This Job
Common parts shoppers buy for U0100 Lost Communication with ECM/PCM.
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OBD2 scanner
Read codes and freeze-frame data before you guess at the fault.
Most diagnostic jobs start with a scan tool and a verified code path.
Check SpecificationsBattery tester
Check cranking and charging health before replacing expensive parts.
A weak battery can mimic alternator or starter problems.
Check SpecificationsMultimeter kit
Confirm voltage, continuity, and sensor power with one simple kit.
A meter is the cheapest way to rule out a bad circuit fast.
Check SpecificationsRelated Resources
Repair guides, symptom pages, and wiring diagrams related to U0100.
OEM Manual Evidence
Browse →Gauge Control System DTCS (2016 2017 2018 2019 2020 2021 2022) — 2013 Acura ILX Base, 2.0L Eng VIN 1 Service Manual ~ LEMON Manuals LEMON M...
Gauge Control System DTCS (2013 2014 2015) — 2013 Acura ILX Base, 2.0L Eng VIN 1 Service Manual ~ LEMON Manuals LEMON Manuals: Repair Knowl...
Driving Support DTCS (2016 2017 2018 2019 2020 2021 2022) — 2013 Acura ILX Base, 2.0L Eng VIN 1 Service Manual ~ LEMON Manuals LEMON Manual...
Keyless Access Power Control Unit DTCS (2013 2014 2015) — 2013 Acura ILX Base, 2.0L Eng VIN 1 Service Manual ~ LEMON Manuals LEMON Manuals:...
Related Symptoms
Browse →Related Codes
Communication lost between the ECM and transmission control module.
The entire CAN bus network has stopped communicating. Major system failure.
Communication error within the ECM or between the ECM and scan tool.
Frequently Asked Questions
- What is the CAN bus?
- CAN bus is the communication network that lets all vehicle modules (ECM, TCM, ABS, etc.) talk to each other.
- Can a loose connector cause U0100?
- Yes — a corroded or loose connector at the ECM is a common cause. Check all ECM connectors first.
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Author & Review
Published by AllOEMManuals, founded by Lyndon Bedford, an automotive technician with 20 years of experience. He owned and operated a mechanic shop in Hurst, Texas from 2014 to 2022 and continues hands-on repair work.
Content may combine manual references, general repair templates, and AI-assisted drafting. Confirm the source, vehicle configuration, and applicability before working. Report corrections through our contact page.
Last updated: 2026-10-29