The Quick Answer above is the generic definition. What follows is the model-specific detail for the Volkswagen models that log U0100.
DTC/U0100·Volkswagen
U0100 on Volkswagen: Causes, Symptoms and Fix Cost
Quick Answer
Critical SeverityNot safe to driveVolkswagen
U0100 on a Volkswagen sets when another control module stops receiving CAN messages from the ECM/PCM. It's a communication failure, not an engine mechanical fault, and it usually prevents the car from starting or keeps it in severe limp mode.
Typical repair cost, all makes€5 - €2200
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VW Golf Mk5/Mk6 (1.9 TDI, 2.0 TSI)
2004-2013VAG equivalents are stored as 'no communication with engine control module' in the CAN gateway (J533). Common on cars with driver footwell water leaks from a clogged plenum drain, which kills the comfort control module (J393) and floods the convenience CAN.
What causes U0100 on a Volkswagen?
Beyond the generic causes listed on the main U0100 page, these are the patterns noted for Volkswagen models:
VW Golf Mk5/Mk6 (1.9 TDI, 2.0 TSI)Failed J533 CAN gateway behind the dash fuse panel
VW Golf Mk5/Mk6 (1.9 TDI, 2.0 TSI)Water damage to J393 comfort module in the driver footwell
VW Golf Mk5/Mk6 (1.9 TDI, 2.0 TSI)Broken wires in the door harness (bend point at the hinge) breaking bus continuity
How to diagnose U0100 on a Volkswagen with OBD2
Follow these steps to pinpoint the root cause of U0100:
- Load-test the battery and confirm at least 12.4V resting, 9.6V minimum during crank. Bus faults below 11V during crank are common and mask the real cause.
- Scan every module and log which ones report U0100 plus any companion U-codes. One reporter points to wiring at that module, multiple reporters point to the ECM or the bus itself.
- Check ECM-related fuses and relays in both the underhood and interior fuse boxes against the wiring diagram, including battery-fed and ignition-fed circuits.
- Measure ECM power and ground at the module connector, key on: battery voltage on B+ pins, under 0.1V drop on ground pins referenced to the negative battery post.
- With the ignition off, give the modules a couple of minutes to go to sleep, then measure resistance across DLC pins 6 and 14. Expect about 60 ohms (two 120-ohm terminating resistors in parallel). 120 ohms means one terminator or half the bus is missing, and much lower means a short.
- Backprobe CAN-H and CAN-L at the ECM connector, key on. Both lines should idle around 2.5V, with CAN-H rising and CAN-L falling during traffic. An oscilloscope makes this obvious.
- If the bus is shorted or flooded, disconnect suspect modules one at a time until communication returns to identify the offender.
- Only after power, grounds, fuses, and bus wiring are verified good, swap in a known-good ECM to confirm before ordering a replacement.
How much does U0100 cost to fix on a Volkswagen? (EUR)
Estimated repair costs for U0100 in EUR, compiled across makes. Expect Volkswagen parts and labour towards the upper end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Codes related to U0100
These codes are often seen alongside U0100 or point to related issues, on any make:
Looking for the full U0100 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main U0100 guideSkanyx · Volkswagen
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