The PACCAR MX P127C page of the 2013 PACCAR MX Diagnostic Service Manual is the manufacturer reference for diagnostic trouble code P127C, described in the manual as “EGR pressure difference – Data erratic, intermittent, or incorrect”. It is a 5-page PDF section covering EGR pressure difference diagnostics on EPA2013 PACCAR MX engines, and it keeps the same layout as every other code page in that manual.
Document details and coverage
| Brand | PACCAR |
| Model coverage | PACCAR MX engines, EPA2013 emissions |
| System group | DTCs / MX Engines (EPA2013) |
| Source publication | 2013 PACCAR MX Diagnostic Service Manual |
| Fault code | P127C |
| Subject | EGR pressure difference |
| Pages | 5 |
| File size | 0.5 MB |
| Format | |
| Language | English |
What PACCAR MX P127C means
The manual files P127C as a 2 trip MIL code with 3 drive cycle recovery, readiness group None and freeze frame type Generic. The diagnostic runs when engine speed is between 1050 and 1900 rpm, EGR valve position is more than 25% and the difference between boost pressure and pressure before the turbine is more than 0.25 bar [3.6 PSI]. The code sets when the PCI ECU (D420) detects that measured EGR gas mass flow differs too much from the expected value for more than 40 seconds, and it changes to inactive when the fault is no longer detected.
Possible causes and technical data
- Contaminated EGR pressure difference sensor venturi
- EGR pressure difference sensor deviation
- EGR temperature sensor deviation
- Boost temperature sensor deviation
The sensor (F751) measures EGR gas pressure before and after a venturi between the EGR cooler and the intake, and is cooled by the engine cooling system because its operating temperature is limited to 125°C [257°F]. The wiring check uses connector F751 and lists 5 V with the ignition keyed on. The page then runs 6 numbered troubleshooting steps, each with its own step ID, starting from a visual inspection of connectors and harness with the ignition off. The manual warns against back probing and tells the technician to rerun the test in DAVIE before judging whether anything changed.
Who needs this PACCAR MX P127C manual page
Heavy-duty technicians, fleet shops and independent workshops diagnosing Kenworth and Peterbilt trucks with EPA2013 PACCAR MX engines use this page to confirm what the ECU actually measured before parts are ordered. For engine literature, dealer locations and support contacts beyond this single code, start at the PACCAR corporate website.
The complete PACCAR MX P127C extract from the 2013 PACCAR MX Diagnostic Service Manual is filed in the DiagTechPro manuals library, where the 5-page PDF can be viewed or downloaded with a free account.
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