Diesel Trouble Codes

P203F — Exhaust Gas Temperature Sensor Circuit Range/Performance Bank 1 Sensor 2 (L5P Duramax)

Exhaust Gas Temperature Sensor Circuit Range/Performance Bank 1 Sensor 2

Updated September 2, 2026

What it means

The ECM has detected the exhaust gas temperature sensor circuit for bank 1 sensor 2 is reporting a signal outside the expected range or is performing inconsistently. On the L5P Duramax this code applies to the emissions system and is listed among DEF/SCR-related codes for this platform.12

Most likely causes

  1. Exhaust gas temperature sensor (bank 1 sensor 2) electrical fault or out-of-range signal — Wiring, connector corrosion, or sensor internal failure causing the circuit to read outside expected range.1
  2. Exhaust system heat-related wiring/connector degradation — High-temperature exposure can degrade harness/connector integrity for the EGT sensor circuit, leading to intermittent or out-of-range readings.1
  3. ECM signal processing anomaly for the EGT circuit — ECM detects inconsistent performance of the sensor circuit under operating conditions.1

How to diagnose

  1. Verify code P203F is present and check freeze-frame data for engine conditions at set.
  2. Inspect EGT sensor bank 1 sensor 2 wiring and connector for heat damage, corrosion, or loose terminals.
  3. Measure sensor circuit resistance and reference/return voltages per service information; compare to expected range.
  4. Monitor live EGT sensor data during a controlled drive cycle to identify intermittent out-of-range behavior.
  5. If circuit tests normal, evaluate ECM inputs and related emissions system data for plausibility.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by location and shop; obtain a quote before proceeding.

When to see a pro

If diagnosis requires exhaust disassembly, high-temperature sensor replacement, or ECM reprogramming, have a qualified diesel technician perform the work.

Sources

  1. Curated DTC seed — L5P Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — L5P Duramax (curated) ↩︎