The ECM detects that the conversion efficiency of the second SCR catalyst on bank 1 is below the calibrated threshold. NOx slip past catalyst 2 is too high.
Medium severity. Can I keep driving?You can usually keep driving in the short term, but get it repaired soon: on many diesels, the warning eventually limits starting or engine power.
Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Most likely causes
- Catalyst 2 aged or contaminated
- Reductant dosing insufficient for cat 2
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P2C7A means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- C: Subsystem depends on the code range
- 7A: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2C7A?
You can usually keep driving in the short term, but get it repaired soon: on many diesels, the warning eventually limits starting or engine power.
What causes code P2C7A?
The most common causes are: catalyst 2 aged or contaminated; reductant dosing insufficient for cat 2.
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.