PACCAR MX P0108 is the fault code page for “Boost pressure – Voltage too high or short circuit to supply on ECU (D420) pin (A51)” in the 2013 PACCAR MX Diagnostic Service Manual. PACCAR publishes it for engines in the EPA 2013 emissions family, and it is worked with the DAVIE diagnostic software.
What this fault code means
Boost pressure sensor F802 sits in the inlet manifold near cylinder 1. Its output sets the smoke limit, the calculated soot and NOx emissions, and the exhaust gas mass flow used for DEF dosing by the EAS-3 system.
Set and reset conditions
The code sets when the PCI ECU detects that the sensor output voltage is too high. The manual adds an important caution: this fault cannot be cleared from the ECU memory, and the PACCAR Engine Support Center must be contacted for further instructions.
PACCAR MX P0108 wiring and technical data
ECU D420 and boost pressure sensor F802 share three circuits, and the manual gives the pin pairs so a breakout measurement lands on the right wire. Sensor pins 2 and 4 should show 5 V with the ignition keyed on. The fault code information block records it as 1 trip MIL, 3 drive cycle recovery, readiness group none, freeze frame type Comprehensive.
| D420 pin | F802 pin | Function |
|---|---|---|
| A39 | 4 | Ground |
| A47 | 2 | Power supply |
| A51 | 1 | Signal, boost pressure |
Possible causes and working notes
- Faulty wiring
- Faulty connection
- Faulty sensor
The sensor cannot be tested with a multimeter or oscilloscope, so the manual routes you to DAVIE monitoring plus a wiring check. Work the steps in the printed sequence.
Document details and format
| Field | Value |
|---|---|
| Brand | PACCAR |
| System group | DTCs, MX Engines (EPA2013) |
| Source publication | 2013 PACCAR MX Diagnostic Service Manual |
| Manual page | 115 |
| Pages | 8 |
| File size | 0.6 MB |
| Format | PDF, English |
Applies to PACCAR MX P0108 repairs
The page sits in the DTCs section for MX engines built to the EPA 2013 emissions standard, so it covers trucks running that engine family with the PCI engine control unit. Coverage and dealer support are published on the PACCAR corporate site.
Who needs this PACCAR MX P0108 page
Technicians who see a high boost pressure signal on a PACCAR MX engine and need to know before they start that the stored fault will not clear normally.
The full PDF page is in the DiagTechPro manuals library; a free account downloads it. Keep the PACCAR MX P0108 sheet open next to DAVIE.
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