PACCAR-P229F moderate PACCAR MX ›

NOx Sensor Bank 1 Sensor 2 Circuit

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Can I Drive?

Yes, But Fix Soon

DIY Difficulty

intermediate

Estimated Cost

$500-$4,200

What does PACCAR-P229F mean?

The PACCAR-P229F (PACCAR MX) diesel fault code means: NOx Sensor Bank 1 Sensor 2 Circuit. This is a moderate severity code.

Common Symptoms

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

Probable Causes (Ranked by Likelihood)

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

Step-by-Step Diagnostic Procedure

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.

Frequently Asked Questions

What does PACCAR MX code P229F mean?

PACCAR MX code P229F (NOx Sensor Bank 1 Sensor 2 Circuit) 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 P229F?

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 P229F?

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.