P20EC: SCR NOx Catalyst - Over Temperature Bank 1

What it means

The module detects that the SCR NOx catalyst on bank 1 has exceeded its allowed temperature threshold. It sets the code when measured or calculated catalyst temperature remains above the calibrated limit under monitor conditions.

How it works

The SCR system injects reductant into the exhaust so the NOx catalyst can reduce nitrogen oxides. The module monitors bank 1 catalyst temperature using exhaust-temperature sensor readings or a calculated value. This code sets when that temperature stays above the permitted limit during the monitor.

Common causes

Most likely first.

1. Faulty exhaust temperature sensor
2. Excessive engine or exhaust temperature
3. Incorrect reductant dosing
4. Exhaust restriction
5. SCR catalyst damage

Symptoms

• Check engine light
• Reduced engine power
• Exhaust or emissions warning
• Poor fuel economy

How to diagnose it

1. Read freeze-frame data and live exhaust-temperature readings for bank 1 to see when the over-temperature condition occurred and whether the reading is plausible.
2. Inspect bank 1 exhaust-temperature sensor wiring and connectors for heat damage, corrosion, loose pins, or a sensor exposed to exhaust leaks.
3. Compare the bank 1 sensor readings with other exhaust temperature readings during warm-up and operation to identify a sensor that is biased high.
4. Check for related engine-temperature, DPF-regeneration, reductant-dosing, and exhaust-pressure codes that could point to excess heat or restricted flow.
5. Inspect the bank 1 exhaust path and SCR catalyst for leaks, restriction, or visible heat damage, then verify reductant dosing against the manufacturer's specification.

Common fixes

• Repair damaged wiring or secure a loose exhaust-temperature sensor connector.
• Replace a confirmed faulty bank 1 exhaust-temperature sensor.
• Correct an engine-temperature, DPF-regeneration, or reductant-dosing fault causing excessive exhaust heat.
• Repair an exhaust restriction or leak affecting the bank 1 SCR system.
• Replace a damaged bank 1 SCR catalyst after confirming the sensor readings and upstream causes.

Can I keep driving?

Avoid heavy loads and prolonged driving while the bank 1 catalyst may be overheating; excess heat can damage the catalyst and nearby exhaust components. If power is reduced or an exhaust warning appears, stop when safe and arrange diagnosis.