PACCAR MX P0073 is the fault code chapter the 2013 PACCAR MX Diagnostic Service Manual publishes for “Ambient temperature – Voltage too high or short circuit to supply on ECU D420 pin C78”. The 3-page PDF is PACCAR’s own troubleshooting write-up for EPA2013 MX engines, reproduced exactly as the factory issued it.
Document details and coverage
| Brand | PACCAR |
|---|---|
| Group | DTCs / MX Engines (EPA2013) |
| Fault code | P0073 |
| Fault code information | 1 trip MIL, 3 drive cycle recovery, freeze frame type Comprehensive |
| Source manual | 2013 PACCAR MX Diagnostic Service Manual |
| Pages | 3 |
| File size | 0.4 MB |
| Format | |
| Language | English |
What sets PACCAR MX P0073 active
The diagnostic runs when the sensor output voltage is too high, above 4.89 V. The PCI sets the code when it detects the sensor output voltage is too high, above 4.99 V, or too low, below 3.99 V. The fault code changes to inactive immediately after the diagnostic runs and passes.
Component and wiring checks
- Pin C56 ground for the ambient temperature sensor (F748) at 0 VDC
- Pin C78 input signal at 5 VDC open voltage with the connector detached
- A sensor resistance table from 315–336 kΩ at -40°F [-40°C] down to 1.2–1.3 kΩ at 176°F [80°C]
Possible causes and repair notes
- Faulty wiring
- Faulty connector
- Faulty sensor
The procedure is worked with a breakout harness where needed, back probing is not recommended because it can damage the harness, and the ignition is kept off while connectors are handled. If the supply voltage measures below 5.5 volts the engine harness is replaced and the verification drive cycle is run with DAVIE connected. Company and product background is on the official PACCAR website.
Who needs this PACCAR MX P0073 chapter
Heavy-duty diesel technicians and fleet shops reach for PACCAR MX P0073 when the code lands on a DAVIE scan and the repair has to follow the factory sequence instead of guesswork.
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