PACCAR MX P109C is the diagnostic trouble code documented on this 4 pages extract from the 2013 PACCAR MX Diagnostic Service Manual, published by PACCAR for EPA2013 MX engines. PACCAR prints the fault as “Common rail pressure release valve – Current too low or open circuit on ECU D420 pin C4”, in the manual’s standard fault code layout.
Document details for PACCAR MX P109C
| Brand | PACCAR |
|---|---|
| Model coverage | PACCAR MX engines, EPA2013 emissions level |
| System / group | DTCs / MX Engines (EPA2013) |
| Source publication | 2013 PACCAR MX Diagnostic Service Manual |
| Fault code | P109C — Common rail pressure release valve – Current too low or open circuit on ECU D420 pin C4 |
| Pages | 4 |
| File size | 0.5 MB |
| Format | |
| Language | English |
Fault code summary and monitor data
The manual lists 1 trip MIL with 3 drive cycle recovery, no readiness group and a fuel freeze frame type. No diagnostic condition information is printed for this entry.
- Code number
- Fault code description
- Fault code information
- Description of component(s)
- Set condition of fault code
- Reset condition of fault code
- Possible causes
- Diagnostic Step-by-Step
- Verification Drive Cycle
Component and system background
The common rail pressure release valve controls rail pressure when normal rail pressure control fails, and acts as a pressure limiter so rail pressure does not exceed 3250 bar plus or minus 300 bar in emergencies. It is part of the common rail and is not supplied as a separate part. If it is not electronically controlled it stays closed and opens at roughly 320 bar plus or minus 70 bar.
Set and reset conditions for PACCAR MX P109C
The code is set when the high pressure common rail fuel pressure relief valve current feedback is less than 0 A, on ECU D420 pin C4, and it goes inactive immediately after the diagnostic runs and passes. No possible causes are listed. Engine torque is reduced while the code is active, and a replacement valve requires the stored control current in the PCI ECU to be reset with DAVIE.
Applies to EPA2013 MX engines
The PACCAR MX P109C entry sits in the DTCs / MX Engines (EPA2013) section, so it applies to PACCAR MX engines built to that emissions level. Manufacturer product information is published on the PACCAR corporate website.
Who needs the PACCAR MX P109C fault code page
Technicians reading a live code, foremen writing an estimate and fleet managers deciding whether a truck stays in service all need the manufacturer wording rather than a generic code list.
The full PDF for MX P109C is in the DiagTechPro manuals library; a free account is required to download it.
Related manuals library
