01 Steering Wheel Feels Loose? Uneven Tire Wear? Don't Ignore … • 02 What Causes the ABS Light to Come On and How to Fix It • 03 The Critical Engine Element That Secretly Pushes Your Fuel … • 04 How to Save Money on Auto Repairs: Tips and Tricks • 05 The Best Cars That Porsche Has Ever Made • 06 iStop: The Revolutionary Brake-Activated Auto Stop-Start Sy… • 07 Can a Bad Alternator Cause Power Steering Problems? • 08 Understanding Gear Ratios: How Transmissions Impact Perform… • 09 You Might Stall On The Highway If You Keep Ignoring That Ra… • 10 Understanding and Troubleshooting Timing Belt Noises •

DTC codes / U06xx · Network communication / U0621

U0621Lost Communication With Exhaust Gas Temperature Sensor Bank 2 Sensor 1

U0621 is a network communication fault where the module that monitors exhaust gas temperature on bank 2, sensor 1 has stopped reporting to the rest of the vehicle's controllers over the CAN (Controller Area Network) bus. The computer has detected that the expected periodic message from that sensor or its control module is missing, not that the sensor itself has failed electrically.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork communication

Symptoms you may notice

  • Illumination of the check engine light or a dedicated communication fault warning on the dashboard.
  • Often no symptoms besides the warning light, because the vehicle may continue to run normally using default values.
  • Possible rough running, reduced power, or poor fuel economy if the engine control module substitutes a fixed exhaust temperature value.
  • A no-start condition or intermittent stalling if the missing module shares a bus segment with other critical controllers.
  • Other unrelated warning lights or messages appearing simultaneously, such as stability control or transmission faults, due to bus-wide communication loss.

Common causes, most likely first

  1. Damaged, corroded, or disconnected wiring at the exhaust gas temperature sensor connector or along the sensor harness.
  2. A failed exhaust gas temperature sensor that has lost its internal communication interface, even if the sensing element still works.
  3. A faulty control module or sensor interface module that is no longer transmitting on the CAN bus.
  4. Open or shorted CAN bus wiring between the sensor module and the gateway or engine control module.
  5. Low battery voltage or a poor ground connection causing the sensor module to drop offline intermittently.
  6. Water intrusion or heat damage in the connector or harness near the exhaust system.
  7. A software or configuration mismatch in a module that was recently replaced or reprogrammed.

How to diagnose and fix it

  1. Connect a scan tool and read all stored codes and live data to confirm U0621 is current and not a history code from a past event.
  2. Visually inspect the exhaust gas temperature sensor connector and harness on bank 2 sensor 1 for corrosion, chafing, or heat damage.
  3. Measure battery voltage and check the sensor module's power and ground circuits with a multimeter before condemning any part.
  4. Perform a resistance and continuity check on the CAN bus wiring between the sensor module and the gateway or engine control module.
  5. If wiring and power are good, substitute a known-good sensor of the same part number and clear the code to see if communication returns.
  6. Check for technical service bulletins or software updates for the affected module, as some communication faults are resolved by reprogramming.
  7. After repair, clear all codes, perform a road test, and verify that U0621 does not return and that all modules communicate normally.

Why this code is often misdiagnosed

  • A U0621 code does not automatically mean the exhaust gas temperature sensor is bad; the fault is in the communication path, so a failed module or a broken wire is just as likely.
  • Technicians often replace the sensor only to find the same code returns because the real problem is a corroded connector pin or a chafed wire near the exhaust that was overlooked.
  • Low battery voltage or a weak ground can cause intermittent U0621 codes that disappear after a jump start, leading owners to believe the problem is fixed when it is not.
  • This code can be set by a module that is still functioning but has lost its CAN bus identifier due to a software glitch, so reprogramming may be needed instead of parts replacement.
  • Other modules on the same bus segment may store unrelated communication codes, so always check for companion codes that point to a shared wiring fault rather than a single sensor.

Can I keep driving with U0621?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads or long trips because the engine may be running on default exhaust temperature values that can affect emissions and fuel economy. If the engine runs roughly or other warning lights appear, stop driving and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage