U0035 — Vehicle Communication Bus A (-) High

U0035 — Vehicle Communication Bus A (-) High. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: damaged CAN bus wiring or short to power/ground, aftermarket equipment interfering with the bus, water ingress in harness junctions.

vehicle network

Is it safe to drive?

Drive with caution Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

How to diagnose with an OBD scanner

  1. Read the code and freeze frame Connect an OBD2 scanner, confirm U0035 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the vehicle network (CAN bus) communication for damage, corrosion, chafing or poor contact.
  4. Subsystem check Measure resistance between CAN-High and CAN-Low at the OBD port with power off — about 60 Ω is healthy.
  5. Subsystem check Scan all modules: the one that does not respond is either the culprit or downstream of the break.
  6. Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0035 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for U0035 (parts and labor, USD, independent shop rates): Replace the faulty control module: $300–$1,500; Remove interfering aftermarket device: $0–$150; Repair CAN wiring or connectors: $100–$400. Overall, fixing U0035 usually costs between $0 and $1,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What is the most common cause of U0035?

The most common causes are: damaged CAN bus wiring or short to power/ground, aftermarket equipment interfering with the bus, water ingress in harness junctions.

How do I diagnose U0035 myself?

Start with a scan: confirm U0035, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the vehicle network (CAN bus) communication, and verify the suspect component against live data before buying parts.

Is it safe to drive with U0035?

Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

What are the symptoms of U0035?

Drivers most often notice: random, hard-to-reproduce electrical glitches, no-start or intermittent starting in some cases, intermittent loss of functions (gauges, windows, steering assist), modules intermittently not communicating with the scanner.

How much does it cost to fix U0035?

Replace the faulty control module — $300–$1,500; Remove interfering aftermarket device — $0–$150; Repair CAN wiring or connectors — $100–$400. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What does U0035 mean?

U0035 (Vehicle Communication Bus A (-) High) is stored when self-diagnostics detect abnormal readings or behaviour of the vehicle network (CAN bus) communication. It belongs to the vehicle network category.

To set U0035, the control module compares live readings of the vehicle network (CAN bus) communication against calibrated limits, usually over several drive cycles. Alongside the code it stores a freeze frame — a snapshot of rpm, load, coolant temperature and vehicle speed at the moment of failure. Reading that snapshot first saves diagnostic time.

What causes U0035?

  • damaged CAN bus wiring or short to power/ground
  • corroded connectors, especially in wet areas
  • aftermarket equipment interfering with the bus
  • a faulty module pulling the bus down
  • water ingress in harness junctions
  • poor grounds or low battery voltage

Common symptoms of U0035

  • random, hard-to-reproduce electrical glitches
  • no-start or intermittent starting in some cases
  • intermittent loss of functions (gauges, windows, steering assist)
  • modules intermittently not communicating with the scanner
  • multiple warning lights on at once

How to diagnose U0035

  1. Connect an OBD2 scanner, confirm U0035 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Visually inspect the wiring harness and connectors related to the vehicle network (CAN bus) communication for damage, corrosion, chafing or poor contact.
  4. Measure resistance between CAN-High and CAN-Low at the OBD port with power off — about 60 Ω is healthy.
  5. Scan all modules: the one that does not respond is either the culprit or downstream of the break.
  6. Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0035 does not return.

How to fix U0035

Start with the cheapest and most common causes before replacing expensive parts:

  • Replace the faulty control module — $300–$1,500
  • Remove interfering aftermarket device — $0–$150
  • Repair CAN wiring or connectors — $100–$400

How much does it cost to fix U0035?

Repair cost depends on which component actually failed. Typical scenarios for U0035 (parts and labor, USD, independent shop rates):

  • Replace the faulty control module: $300–$1,500
  • Remove interfering aftermarket device: $0–$150
  • Repair CAN wiring or connectors: $100–$400

Overall, fixing U0035 usually costs between $0 and $1,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with U0035?

Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

Related OBD2 codes