P229F — NOx Sensor Circuit Range/Performance Bank 1 Sensor 2 — 6.7 Cummins (SCR / DEF)
Diagnostic reference for 6.7 Cummins (SCR/DEF) 2013–present.
What it means
Generic definition: the downstream (bank 1 sensor 2) NOx sensor signal is outside its expected range or not performing as expected. On the 6.7L Cummins SCR system this is the tailpipe-side NOx sensor.1
Most likely causes
- NOx sensor (bank 1 sensor 2, tailpipe side) degraded or contaminated — Sensor output drifts out of expected range or responds slowly; typical for the downstream NOx sensor on this platform.1
- Wiring/connector fault for the downstream NOx sensor — Chafed, corroded or loose connector and harness leading to intermittent or out-of-range signal.1
- Exhaust leak near the downstream NOx sensor — False air ingress upstream of the sensor skews NOx readings and triggers range/performance detection.1
- SCR/aftertreatment condition affecting measured NOx — Reduced SCR efficiency or abnormal exhaust conditions can move the downstream NOx signal outside the calibrated window.1
How to diagnose
- Verify freeze-frame and related SCR/NOx codes; confirm P229F is present with bank 1 sensor 2 identified as downstream/tailpipe side.
- Inspect the downstream NOx sensor connector and harness for corrosion, moisture intrusion, pin damage and chafing along the exhaust routing.
- Check for exhaust leaks at the sensor boss, nearby joints and clamps; look for soot tracks or audible leaks that admit ambient air.
- Review live NOx sensor data for plausible voltage/current and response during steady cruise; compare upstream vs downstream behavior for reasonableness.
- Inspect SCR system basics (DEF quality, dosing, DPF/SCR temperatures) for conditions that could drive abnormal downstream NOx, without performing high-pressure fuel injection service.
Specs and test values
| Check | Normal reading | When to measure | Source |
|---|---|---|---|
| DEF urea concentration | 32.5% (check with a DEF refractometer) | Sample from the tank | Ram service bulletin 25-005-14 (Diesel Exhaust Fluid) |
Common mistake to avoid
Replacing sensors, the doser or the SCR catalyst before testing the DEF. Old, heat-stored or diluted DEF loses strength and sets the same efficiency codes. Check it with a refractometer first. Source: Ram service bulletin 25-005-14 (Diesel Exhaust Fluid).
Parts and tools you may need
- Scan tool with Cummins enhanced NOx/SCR data
- Digital multimeter
- Inspection light and mirror
- Exhaust leak detection spray or smoke tool (non-intrusive)
Tools you’ll need
- bi-directional scan tool — Reads live NOx sensor voltages and commands SCR/DEF tests to confirm the downstream sensor is out of range.
- digital multimeter — Checks NOx sensor heater power, ground and signal circuits for opens, shorts or corrosion.
- exhaust gas analyzer — Measures actual tailpipe NOx to verify if the downstream sensor reading is plausible.
- inspection mirror — Lets you see the downstream NOx sensor boss and nearby joints for leaks or contamination without removing shields.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| Wiring or connector repair | $10–$100 | 1–4 hrs | DIY with tools and a manual |
| Exhaust manifold, gasket or up-pipe leak repair | $50–$400 | 2–6 hrs | DIY with tools and a manual |
| NOx sensor | $250–$800 | 0.5–2 hrs | DIY with tools and a manual |
| SCR catalyst | $2,000–$4,500 | 1–4 hrs | Shop |
Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.
When to see a pro
If the code returns after connector/harness and exhaust-leak inspection, or if SCR efficiency codes accompany P229F, have a qualified diesel technician evaluate the NOx sensor and SCR system with OEM diagnostics.
Check for recalls
Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.
Sources
Repair videos: P229F on the 6.7 Cummins '13+
Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.
Spotted an error, or something missing? Tell us
Run a 6.7 Cummins (SCR / DEF)? This goes straight to the editor — it is not published.