U0142

Lost Communication With Body Control Module B

Network / Communication Network/Communication CAN Bus Communication 🟡 Moderate — Fix within a week ⚠️ Drive with Care
💬

What This Actually Means

In plain language — no jargon

Your car's main computer lost contact with the body control module, which handles things like lights, windows, and door locks—like two phones in the same car losing their connection. This is a communication problem, not a problem with any single part.

⚡

Symptoms You May Notice

3 known symptoms for this code
Multiple electrical systems malfunction (lights, wipers, power windows, locks)
Dashboard warning lights illuminate or flickering
Vehicle may enter limp mode or reduced functionality
🔬

How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM communicates with Body Control Module B via the CAN bus network at regular intervals, expecting acknowledgment messages within specific timeouts. If the ECM fails to receive expected responses for a predetermined duration, it sets this fault code.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
CAN Bus Message Response Time < 100ms per message cycle > 500ms or no response for 2+ cycles
CAN Bus Signal Voltage 2.5V - 4.5V (dominant/recessive) < 2.5V or > 4.5V, open circuit, or short
🔧

Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Battery terminals and connections
Clean corrosion from battery terminals and ensure all ground connections are tight.
2
CAN bus wiring and connectors
Inspect CAN bus harness under dashboard and at body control module for loose connectors, damaged insulation, or pinched wires.
3
Body Control Module B connector
Disconnect and reconnect the BCM-B connector to reseat pins and clear any corrosion causing poor contact.
⚠️

When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code U0142 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
🔄

How to Clear Code U0142

What happens after you fix the fault

Once the fault is repaired, U0142 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.