What does it mean?
P1259 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: VTEC System Malfunction (Bank 1) . This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms
- The MIL is on and only one bank switches, giving an uneven power delivery
- Engine pulls poorly above mid range and sounds different from normal at high rpm
- Reduced power and slower acceleration, especially when fully warm
- Slight increase in fuel consumption
- No obvious problem at idle or in traffic, so the fault is easy to overlook
Likely causes
- Restricted oil supply to the Bank 1 solenoid because of a blocked filter screen
- Bank 1 solenoid spool sticking or its winding failing intermittently when hot
- Oil pressure switch for Bank 1 giving no change of state
- Engine oil low, degraded or of the wrong viscosity, especially in cold weather
- Chafed or oil-soaked wiring to the Bank 1 solenoid connector at the cylinder head
- Internal oil passage restriction or a leaking gallery plug on that bank only
- Worn rocker components on Bank 1 that no longer lock at high lift
How to fix it
- Confirm oil level, grade and condition before testing anything electrical
- Command the Bank 1 system on at raised rpm and watch the corresponding oil pressure switch feedback on live data
- Compare the Bank 1 readings with the other bank; the difference points straight at the faulty side
- Remove the Bank 1 solenoid, clean or replace its filter screen and check the spool moves freely
- Measure winding resistance of the Bank 1 solenoid and check its supply, ground and connector for oil intrusion
- Test the Bank 1 oil pressure switch for correct switching and check its wiring
- Fit the proven faulty part, refill with the specified oil and verify on a road test that both banks now switch together