PACCAR J1939 diagnostic procedure is documented in Chapter 12 of the PACCAR Electrical System Service Manual, publication PM819010/KM815054, revised 04/01/2010. The symptom it addresses is multiple V-CAN (J1939) databus gauges inoperative, or an automated transmission that will not shift properly. Only a Volt-Ohm Meter is needed, so it suits any shop. This excerpt runs 7 pages and starts at manual page 12-104.
What PACCAR J1939 diagnostic procedure covers
V-CAN databus gauges receive their data from the J1939 data link through the engine ECU, which in turn collects it from sensors on the engine and transmission. This PACCAR J1939 diagnostic procedure therefore tests the wiring and the terminating resistors rather than any single gauge. The manual is explicit that failure of any one of these procedures will render the J1939 data link inoperative, and that the tests must be run in order with every resistance reading recorded.
Document details and coverage
| Brand | PACCAR |
|---|---|
| Model coverage | PACCAR trucks with a V-CAN (J1939) databus, 2005-2010 |
| System / group | Chapter 12 Electrical System – DTCs, Cab (2005-2010) |
| Publication no. | PM819010/KM815054 |
| Revision | 04/01/2010 |
| Pages | 7 |
| File size | 0.3 MB |
| Format / language | PDF, English |
Procedure sections in this excerpt
- Lite Terminating Resistor Test Procedure – each resistor should read approximately 120 ohm
- Lite Short Circuit Test Procedure – any resistance reading indicates an undesirable short
- Lite Short to Chassis Ground Test Procedure – both terminals checked against chassis ground
- Lite Open Circuit Test Procedure – circuit resistance should be approximately 60 ohm with the resistors refitted
- Lite Diagnostic Procedures Conclusion – reconnect and retest with ECU diagnostic tools
- Overall J1939 schematic illustration
Wiring and pin references
The open-circuit test is where most shops get their answer. With the terminating resistors reinstalled and the engine and ABS ECU connectors still unplugged, the circuit should measure roughly 60 ohm. Zero or no reading means an open circuit, so look for cut wires or loose connections. A reading significantly higher than 60 ohm points to corrosion at the terminal connectors. The conclusion section adds that if the tools still will not talk to an ECU after wiring, power and ground all check out, the ECU itself is suspect and should be swapped for a test unit.
Who needs this PACCAR J1939 diagnostic procedure manual
Any technician chasing several dead gauges at once, or a transmission that shifts badly, before replacing parts that were never faulty. Confirm coverage against the official PACCAR corporate site before ordering parts.
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