PACCAR MX P009A is the fault code chapter the 2013 PACCAR MX Diagnostic Service Manual publishes for “Ambient temperature – Data erratic, intermittent, or incorrect”. The 6-page PDF is PACCAR’s own troubleshooting write-up for EPA2013 MX engines, reproduced exactly as the factory issued it.
Document details and coverage
| Brand | PACCAR |
|---|---|
| Group | DTCs / MX Engines (EPA2013) |
| Fault code | P009A |
| Fault code information | 2 trip MIL, 3 drive cycle recovery, freeze frame type Comprehensive |
| Source manual | 2013 PACCAR MX Diagnostic Service Manual |
| Pages | 6 |
| File size | 0.5 MB |
| Format | |
| Language | English |
What sets PACCAR MX P009A active
The chapter covers the smart humidity sensor that communicates with the PCI ECU over E-CAN and measures relative humidity, pressure and temperature of the air drawn in before the compressor. The code reports that the ambient temperature data is erratic, intermittent or incorrect. The verification drive cycle asks for engine load, then a road with a minimum speed limit of 50 mph, the highest gear possible with engine speed between 1100 and 1500 rpm and cruise control set, for roughly 3 to 5 miles.
Component and wiring checks
- Smart humidity sensor communication with the PCI ECU over E-CAN
- Relative humidity, precompressor pressure and precompressor temperature signals in the inlet air pipe
- Load produced with a loaded trailer, or with the air conditioning and fan switched on if no trailer is available
Possible causes and repair notes
- An implausible reading from the humidity sensor in the inlet air pipe
- E-CAN communication problems between the sensor and the PCI ECU
- Wiring or connector faults on the sensor circuit
The manual sets out what each of the three measured properties does: relative humidity feeds the calculated NOx emission, precompressor temperature feeds soot formation, exhaust gas pressure before the turbine, torque limits in cold ambient conditions or at high altitude, and the detection of VTG surge, while precompressor pressure corrects pressure before the turbine and the calculated temperature after the compressor. Company and product background is on the official PACCAR website.
Who needs this PACCAR MX P009A chapter
Heavy-duty diesel technicians and fleet shops reach for PACCAR MX P009A when the code lands on a DAVIE scan and the repair has to follow the factory sequence instead of guesswork.
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