NOx Sensor Circuit Low Input
The PACCAR-P2202 (PACCAR MX) diesel fault code means: NOx Sensor Circuit Low Input. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- intermediate
- Estimated cost
- $500-$4,200
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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
Frequently Asked Questions
What does PACCAR MX code P2202 mean?
PACCAR MX code P2202 (NOx Sensor Circuit Low Input) 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 P2202?
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 P2202?
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
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.
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 P2202 as a generic OBD-II code)
P2202 on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown:
Commonly Affected Vehicles
- 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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