U0621: Lost Communication With Exhaust Gas Temperature Sensor Bank 2 Sensor 1

What it means

A control module has stopped receiving expected network messages from the exhaust gas temperature sensor on bank 2, sensor 1. The code indicates a communication fault; the effect depends on how the vehicle uses that sensor.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test

How it works

Exhaust gas temperature sensor bank 2 sensor 1 measures exhaust heat at the first monitored position on engine bank 2, typically before the catalytic converter. U0621 sets when expected network messages from this specific sensor stop arriving, leaving systems that use its reading without direct bank 2 temperature data.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Warning light or message related to the affected system
• Exhaust temperature data may be unavailable

How to diagnose it

1. Scan all modules for communication codes and record freeze-frame data to identify whether bank 2 sensor 1 failed alone or during a broader network or voltage problem.
2. Check live data for bank 2 sensor 1 and compare it with bank 1 sensor 1 and other exhaust temperature readings.
3. Inspect the bank 2 sensor 1 connector and hot-zone wiring for heat damage, chafing, corrosion, or loose terminals.
4. Verify the sensor module's power and ground using the manufacturer's wiring information.
5. Test the network circuit serving bank 2 sensor 1 for opens and shorts according to the manufacturer's procedure.
6. If the circuit and supply are sound, confirm the module has stopped transmitting before replacing it.

Common fixes

• Repair heat-damaged or chafed wiring at bank 2 sensor 1.
• Clean or repair loose or corroded connector terminals.
• Restore the sensor module's power or ground, or repair a network wiring fault.
• Replace the bank 2 sensor 1 module if its supply and network wiring pass but it remains offline.

Can I keep driving?

Avoid heavy loads and prolonged high-speed driving until bank 2 temperature data is restored, especially if an emissions or aftertreatment warning appears. Continued operation may impair temperature-based catalyst protection or regeneration.