Drivers typically notice one or more of the following after the U0620 code appears:
These signs appear suddenly and persist until the communication fault is resolved.
Physical damage to the harness that carries the EGT signal (abrasion, heat exposure, or rodent chewing) creates an open circuit or intermittent resistance. The PCM interprets the loss as a sensor failure and logs U0620.
Moisture ingress, brake‑dust buildup, or improper tightening can corrode the sensor’s connector pins. Even a small increase in contact resistance disrupts the high‑frequency data stream required for temperature monitoring.
The PCM’s internal communication bus (CAN or LIN) may suffer from a failed transceiver, firmware corruption, or a solder‑joint fracture. When the bus can’t acknowledge the sensor’s signal, the module logs a lost‑communication code.
A sensor that has shorted internally or lost its internal reference can stop transmitting any data. While the sensor itself is a hardware part, the PCM’s inability to recover communication still triggers U0620.
After a major ECU flash, a software version that does not support the specific sensor configuration can cause the PCM to reject incoming data, resulting in a communication loss.
– Connect a professional scan tool, retrieve the U0620 code, and note any accompanying codes (e.g., P0455, C1234). Freeze‑frame parameters often show the engine load and temperature at the time of the fault, confirming whether the PCM was actively protecting the exhaust.
– With the engine running, monitor the EGT sensor’s voltage or temperature reading. A flat line at 0 °C or a constant high value indicates no valid data. Compare Bank 1 Sensor 2 with Bank 1 Sensor 1; a discrepancy suggests a wiring or sensor issue.
– Disconnect the sensor connector and perform a 2‑wire continuity check from the PCM pin to the sensor harness. Resistance should be within the manufacturer’s specification (typically < 1 Ω). Any open circuit or high resistance points to harness damage.
– Visually examine the connector for corrosion, bent pins, or broken clips. Clean with an electrical contact cleaner and re‑torque to the specified torque (usually 5–7 Nm). Re‑test live data after cleaning.
– Use a scan tool that can perform a “PCM communication test” or “CAN bus integrity check.” The tool sends a request to the PCM and verifies the response. Failure indicates a PCM‑level fault rather than a sensor or wiring problem.
– If the PCM passes hardware tests but the code persists, update the PCM firmware to the latest version and re‑calibrate the EGT sensor parameters. Many manufacturers require a specific calibration routine after a PCM flash.
– When the PCM’s internal transceiver or bus driver is identified as defective, a repair may be possible with a certified re‑soldering service. However, repeated communication failures often make replacement the more reliable long‑term solution.
Cost Estimates
Modern control modules are complex, integrating power‑train control, emissions monitoring, and vehicle‑security functions. When a PCM’s communication circuitry fails, a simple repair often provides only a temporary fix; the underlying board damage or firmware incompatibility can quickly re‑appear.
Flagship One specializes in VIN‑matched control modules, providing a plug‑and‑drive solution backed by a comprehensive warranty. Because each unit is pre‑programmed to your vehicle’s exact specifications, installation eliminates the need for on‑site coding and reduces the risk of post‑repair failures. When diagnostic results point to a PCM communication fault that cannot be resolved through re‑programming or wiring repair, a Flagship One replacement ensures reliable, long‑term operation.
Service Recommendation: Most issues related to this fault are diagnosed and corrected through inspection, wiring repair, and calibration rather than module replacement. For modules not typically replaced through aftermarket suppliers, diagnosis and repair should be performed by a certified automotive technician with access to factory service information and tooling.