PACCAR MX P0128 is the fault code page for “Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)” 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
The manual describes P0128 as a coolant thermostat code: the coolant temperature stays below the thermostat regulating temperature. The engine is running cooler than the thermostat should allow, which classically points at a thermostat stuck open rather than at the temperature sensor circuit.
PACCAR MX P0128 page structure
This is a one-page entry. It carries the code number and the fault code description, then the standard headings used throughout the manual, but the detail under them is not printed on this page. Instead the page states: Please Contact the Engine Support Center.
- Description and location of component
- Diagnostic condition, set condition and reset condition
- Electrical diagrams and technical data
- Possible causes and additional information
- Diagnostic step-by-step and verification drive cycle
Treat the page as a confirmed identification of the code plus an instruction on where the full procedure lives. That is still worth having in writing when a customer asks why the shop is calling the factory.
Document details and format
| Field | Value |
|---|---|
| Brand | PACCAR |
| System group | DTCs, MX Engines (EPA2013) |
| Source publication | 2013 PACCAR MX Diagnostic Service Manual |
| Manual page | 154 |
| Pages | 1 |
| File size | 0.3 MB |
| Format | PDF, English |
Applies to PACCAR MX P0128 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 P0128 page
Technicians investigating slow warm-up, poor cab heat or cold-running complaints on a PACCAR MX engine before they condemn a thermostat.
The full PDF page is in the DiagTechPro manuals library; a free account downloads it. Keep the MX P0128 sheet open next to DAVIE.
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