NOx Sensor Heater Sense Circuit High
The PACCAR-P2209 (PACCAR MX) diesel fault code means: NOx Sensor Heater Sense Circuit High. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- intermediate
- Estimated cost
- $500-$4,200
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View pilot availability →What Are the Symptoms of PACCAR-P2209?
- Check Engine Light with progressive derate
- DEF warning and 5 mph limp eventually
- High DEF consumption
- Failed emissions / CARB inspection
- Possible no-restart inducement active
What Causes PACCAR-P2209? (Most Likely First)
- Failed inlet or outlet NOx sensor (most common MX cause) Very Likely
- Crystallized DEF at doser restricting flow Likely
- DEF quality out of spec Possible
- SCR catalyst aged / contaminated (end-of-life) Possible
- Exhaust leak upstream of SCR causing false readings Possible
Can I Still Drive with PACCAR-P2209?
Short distances only. PACCAR-P2209 is rated moderate severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
Frequently Asked Questions
What does PACCAR MX code P2209 mean?
PACCAR MX code P2209 (NOx Sensor Heater Sense Circuit High) is a moderate-severity diagnostic trouble code set by the engine or aftertreatment control module on MX-11 and MX-13 engines in Kenworth and Peterbilt trucks. It indicates a fault in the aftertreatment system that should be diagnosed with DAVIE4 or PACCAR ESA.
Can I drive a Kenworth or Peterbilt with PACCAR P2209?
Possibly — short distances may be OK, but ignoring the fault risks progressive damage, regen failure, or derate. Address promptly.
How much does it cost to fix PACCAR MX P2209?
Typical repair runs $500-$4,200. Sensor or wiring repairs are at the low end; injector, DEF pump, DPF, or EGR cooler jobs are at the high end. Dealer-level DAVIE4 software is often required for programming or calibration after parts replacement.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose PACCAR-P2209?
Clear codes and operate truck through full duty cycle. Re-scan — chronically-failing NOx sensor will re-set quickly.
Graph both NOx sensor values at idle and cruise with DAVIE4. Inlet should read 200-800 ppm; outlet should drop near zero.
Refractometer-test DEF. Concentration below 30% urea indicates contamination.
Inspect SCR inlet/outlet for leaks or damage with smoke machine.
If both sensors and DEF check out, replace aged SCR catalyst and reflash CEM.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J1939-73Application Layer: Diagnostics (defines the SPN/FMI fault-identifier framework)
- SAE J2012Diagnostic Trouble Code Definitions (defines P2209 as a generic OBD-II code)
P2209 on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown:
Which Vehicles Commonly Get PACCAR-P2209?
- Kenworth T680 with PACCAR MX-13
- Kenworth T880 with PACCAR MX-13
- Kenworth W990 with PACCAR MX-13
- Peterbilt 579 with PACCAR MX-13
- Peterbilt 389 with PACCAR MX-13
- Peterbilt 567 with PACCAR MX-13
- Kenworth T440 with PACCAR MX-11
- Kenworth T470 with PACCAR MX-11
- Peterbilt 520 with PACCAR MX-11
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