U0116

Lost Communication With Coolant Temperature Control Module

Network / Communication Network/Communication CAN Bus Fault 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

Your engine computer lost its radio connection to the coolant temperature control module, like a phone losing signal to a tower. Without this communication, the engine can't properly manage cooling fan operation and temperature regulation.

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Symptoms You May Notice

3 known symptoms for this code
Engine running hotter than normal or overheating
Cooling fan not engaging or running constantly
Check Engine Light illuminated with U0116 code
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM expects periodic CAN bus messages from the coolant temperature control module containing real-time coolant temp data and fan control status. When these messages stop arriving within a defined time window (typically 100-500ms), the ECM flags a communication timeout. The module should confirm its presence and operational status through continuous data handshakes.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
CAN Bus Message Timeout Message received every 100-500ms No message received for >500ms
Module Status Active/responding to ECM requests No response or invalid data stream
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
OBD-II Scanner
Clear the fault code and perform a test drive to determine if it's intermittent or persistent communication loss.
2
CAN Bus Wiring Harness
Inspect the wiring between ECM and coolant control module for corrosion, loose connectors, or damage and reseat all connections.
3
Coolant Temperature Control Module
Replace the module if wiring tests pass, as internal failure prevents CAN communication with the ECM.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code U0116 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.
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How to Clear Code U0116

What happens after you fix the fault

Once the fault is repaired, U0116 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.