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If your Kenworth or Peterbilt truck equipped with a PACCAR MX engine is displaying fault code P006B or P006C, you're not alone. These diagnostic trouble codes are commonly encountered by technicians and fleet maintenance professionals working on PACCAR MX-11 and MX-13 engines.
This guide explains what these fault codes mean, the symptoms they can cause, common reasons they occur, and the diagnostic procedures recommended by PACCAR. Whether you're an owner-operator trying to understand a warning light or a professional technician diagnosing a truck in the workshop, this article will help you identify the root cause of the problem.
These faults can appear on various PACCAR MX applications and are generally associated with sensor signal abnormalities detected during ignition-on conditions.
Modern PACCAR engines rely on multiple sensors and electronic control systems to optimize performance, emissions compliance, and fuel efficiency. When the Engine Control Module (ECM) detects a signal that falls outside expected parameters, it stores a Diagnostic Trouble Code (DTC) and may illuminate the Malfunction Indicator Lamp (MIL).
Fault codes P006B and P006C are both related to pressure sensor readings that the ECM considers erratic, intermittent, or incorrect. Although the two codes may sound similar, they involve different sensors and require different troubleshooting procedures.
Fault Code: P006B
Description: Pressure After BPV – Data Erratic, Intermittent, or Incorrect at Ignition ON.
Affected Sensor: Pressure After BPV Sensor (F823)
Fault Type: Sensor signal outside expected operating range.
The Engine Control Module continuously monitors the pressure sensor located after the Butterfly Pressure Valve (BPV). During ignition-on conditions, the ECM compares the pressure reading against calibrated values.
If the signal appears unstable, intermittent, or outside the expected range, the ECM logs fault code P006B and stores it in memory for diagnostic purposes.
Depending on the severity and frequency of the fault, drivers and technicians may observe one or more of the following symptoms:
Several factors can contribute to this diagnostic fault code. The most common causes include:
Before replacing the sensor, inspect the connector pins carefully. Many intermittent P006B faults are caused by poor electrical connections rather than failed components. Always perform a visual inspection before replacing parts.
Reading fault codes is only the first step. To accurately diagnose and repair PACCAR MX engines, professional technicians use dealer-level diagnostic software to access live data, perform tests, clear fault codes, and troubleshoot problems faster.
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PACCAR recommends following a systematic troubleshooting approach to avoid unnecessary parts replacement and reduce diagnostic time.
Many trucks remain operational with this fault code, but the underlying issue should be diagnosed promptly to avoid future drivability concerns or emissions-related problems.
No. Wiring issues and connector corrosion are common causes of intermittent faults. Electrical checks should always be completed before replacing components.
Although it may not immediately disable the vehicle, repeated occurrences indicate that the system requires inspection and repair.
Get access to professional workshop manuals, troubleshooting guides, electrical schematics, service procedures, and OEM repair information used by technicians worldwide.
Continue to Part 2 for the complete P006C fault code explanation, humidity sensor operation, advanced troubleshooting procedures, and PDF download section.
Fault Code: P006C
Description: Pressure Before Turbo (Humidity Sensor) – Data Erratic, Intermittent, or Incorrect at Ignition ON.
Affected Sensor: Pressure Before Turbo / Humidity Sensor (F852)
Fault Type: Sensor signal abnormal during ignition-on validation.
Unlike P006B, which relates to the pressure sensor after the Butterfly Pressure Valve, fault code P006C involves the humidity sensor located before the turbocharger. This sensor provides multiple environmental readings that help the Engine Control Module optimize combustion efficiency and emissions performance.
When the ECM detects a pressure reading that is erratic, intermittent, or outside its expected calibration range, it stores fault code P006C and may illuminate the Malfunction Indicator Lamp (MIL).
The Pressure Before Turbo Sensor (F852), commonly referred to as the humidity sensor, performs several important functions.
This sensor measures:
These measurements allow the ECM to accurately adjust fuel delivery, emissions strategies, and engine performance under varying environmental conditions.
Incorrect humidity and pressure readings can affect combustion calculations, emissions control strategies, and diagnostic validation routines. Even small signal interruptions may trigger P006C.
Drivers and technicians may notice one or more of the following symptoms:
Several factors may contribute to this fault code.
PACCAR recommends a systematic approach when diagnosing this fault.
Before replacing the sensor, technicians should perform the following inspections:
Many P006C faults are intermittent and may be caused by moisture or poor terminal contact. Always inspect connectors thoroughly before replacing expensive components.
In many cases the truck remains operational, but unresolved faults should be diagnosed promptly to avoid future performance concerns.
No. Wiring faults, connector corrosion, and moisture intrusion are common causes of intermittent signal problems.
Yes. PACCAR diagnostic software can be used to clear faults and confirm that the repair was successful.
Not always. Proper electrical inspections should be completed before replacing components.
| Fault Code | Component | Primary Concern |
|---|---|---|
| P006B | Pressure After BPV Sensor (F823) | Pressure signal after BPV |
| P006C | Humidity Sensor (F852) | Pressure before turbo signal |
Need the original PACCAR troubleshooting document covering fault codes P006B and P006C? Download the complete reference guide for future use in your workshop.
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Disclaimer: This article is intended for educational and informational purposes only. Always follow official PACCAR service procedures and safety guidelines when performing diagnostic and repair work.
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