Diesel Trouble Codes

P2201 — Oxygen Sensor Signal Circuit Range/Performance Bank 1 Sensor 1 (6.7 Cummins (SCR / DEF))

Diagnostic reference for 6.7L Cummins SCR/DEF 2013–present. P2201 is a generic oxygen-sensor definition; on this diesel platform the code is used for NOx…

Updated September 2, 2026

What it means

On 6.7L Cummins SCR/DEF trucks P2201 is a NOx-sensor signal range/performance fault, not a gasoline oxygen sensor. The ECM sees the NOx sensor output outside expected range or behaving inconsistently. This can accompany SCR efficiency faults and may lead to derate/limp.12

Most likely causes

  1. NOx sensor (bank 1 sensor 1) degraded or contaminated — Sensor drift, poisoning from oil/coolant/DEF contamination, or age-related response loss causes out-of-range signal. Typical with SCR NOx sensor family faults.12
  2. NOx sensor wiring / connector corrosion or chafing — Exhaust heat and road salt degrade harness/connector; intermittent opens/shorts produce range/performance errors.1
  3. Reference/ground or 5 V supply issue to NOx sensor — Shared ECM supply/ground problems affect sensor bias voltage and signal plausibility.1
  4. Exhaust leaks upstream of NOx sensor — False air ingress skews NOx readings and triggers range/performance faults.2
  5. SCR system performance issues affecting NOx readings — Low DEF dosing, poor DEF quality, or catalyst degradation can drive NOx values outside expected range, setting sensor-range/performance codes alongside P20EE/P204F/P2BAD.2
  6. ECM software / calibration anomaly — Incorrect thresholds or learned adaptations can misinterpret a good sensor signal.1

How to diagnose

  1. Verify code and freeze frame; confirm P2201 is present with SCR/DEF platform and check for companion codes P20EE, P204F, P2BAD, P2202.
  2. Inspect NOx sensor connector and harness for corrosion, oil contamination, heat damage, and chafing along exhaust routing.
  3. Check sensor supply voltage, ground, and signal bias at the ECM connector per service info; look for opens/shorts to power/ground.
  4. Perform NOx sensor response test using scan tool bi-directional controls and compare pre/post catalyst sensor readings under steady cruise.
  5. Inspect exhaust system for leaks upstream of sensor 1; repair leaks before condemning sensor.
  6. Review DEF quality, tank level history, dosing quantity, and recent SCR service; address reductant system faults first.
  7. If no wiring or system faults found, replace NOx sensor bank 1 sensor 1 and re-learn adaptations; confirm code does not return.
  8. If fault persists after sensor and wiring verification, evaluate ECM calibration and consider software update per TSBs.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by model year and location. NOx sensor replacement is common; wiring repairs and SCR service can add cost. Dealer diagnostic time applies.

When to see a pro

High-pressure fuel and exhaust work can be hazardous. If diagnosis points to ECM, internal harness faults, or SCR catalyst concerns, have a qualified diesel technician complete testing and repairs. Do not attempt high-pressure fuel or exhaust repairs without proper training and safety equipment.

Sources

  1. Curated DTC seed — 6.7 Cummins (SCR / DEF) (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — 6.7 Cummins (SCR / DEF) (curated) ↩︎ ↩︎ ↩︎ ↩︎