PACCAR MX P109D is the diagnostic trouble code documented on this 5 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 high on ECU D420 pin C4”, in the manual’s standard fault code layout.
Document details for PACCAR MX P109D
| 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 | P109D — Common rail pressure release valve – Current too high on ECU D420 pin C4 |
| Pages | 5 |
| 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. The diagnostic runs continuously with the ignition on and the engine off, after 10 seconds of ignition ON.
- 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 limits rail pressure when normal control is lost and prevents rail pressure exceeding 3250 bar plus or minus 300 bar. During normal control it is held closed by a duty cycle whose current depends on the required rail pressure, and if it opens the fuel is dumped into the supply pipe of the fuel module.
Set and reset conditions for PACCAR MX P109D
The code is set when the high pressure common rail fuel pressure relief valve current feedback is greater than the threshold value of 2.3 A, and it changes to inactive immediately after the diagnostic runs and passes. No possible causes are listed. Engine torque is reduced while the code is active. A replacement valve requires the stored control current in the PCI ECU to be reset with DAVIE before the repair is validated.
Applies to EPA2013 MX engines
The PACCAR MX P109D 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 P109D 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 P109D is in the DiagTechPro manuals library; a free account is required to download it.
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