Failure phenomenon: a 2004 Honda Accord sedan, equipped with CM6 engine, mileage 160 000 km. Users reflect driving the car engine fault lights up, but not accompanied by any undesirable phenomenon.
Check Analysis: maintenance personnel take the car for detecting a fault diagnostic HDS, fault code read is: P2647 mdash; mdash; VTEC oil pressure switch high voltage circuit. After clearing the fault code with HDS, starting the engine, we observed that, when the engine is idling, the engine malfunction light is not illuminated, the increased engine speed when approaching 3 000 r / min, engine failure lights. Test again, still fault code P2647.
I fault code as prompted, first check VTEC pressure switch circuit, for the power system control unit the PCM E (31P) and two connector pin connector VTEC pressure switch turned off. No. 23 terminal of the phenomenon VTEC pressure switch terminal 1 of the measuring line E (31p) of the connector (FIG. 1), the results of the short-circuit and grounding the power source line is turned to be good, and absent. VTEC pressure switch measuring terminal to the grounding point 2 G101 line is also turned normal. Check concluded VTEC pressure switch line is normal. Then the pressure switch, respectively VTEC, VTEC solenoid valve control unit and a power system for PCM replacement of parts, but the fault persists.
At this point we need to think calmly. VTEC variable valve timing and lift Electronic Control system timing, is employed in the particular case of different intake cam, changing the valve lift and timing change intake air amount, thereby changing the engine output torque. Cam is selected by the power system control unit according to the engine speed, engine load, vehicle speed, coolant temperature and pressure switches and other signal VTEC determined. Powertrain control unit VTEC solenoid valve control operation, the VTEC solenoid valve and operation of the hydraulic control valve is performed, the hydraulic actuator to turn on or off the valve by axial displacement of the hydraulic VTEC. When VTEC solenoid valve is closed, the control oil passage in the pressure relief state, a hydraulic actuator moves in the valve closing direction by the spring force, closing VTEC oil. When the power system controlSystem unit instructs the control VTEC solenoid valve open, the control oil passage in the pressurized state, the control oil pressure applied to the hydraulic control valve side implementation, the hydraulic pressure actuated valve against the spring, moves in the opening direction, thereby turning on the hydraulic VTEC . VTEC oil enters the hydraulic chamber of each valve rocker arm, the synchronous movement of the piston, the primary and secondary rocker arms and an intermediate rocker arm fused together operation, the valve open time extended, the lift is increased. VTEC VTEC pressure switch is responsible for detecting whether the system is in working condition, and transmits the signal to a powertrain control unit.
By observing the engine data stream (FIG. 2) and the analysis showed that, in the VTEC solenoid valve is closed, when the engine speed is raised to 2 747 r / min, VTEC non-normal operation of the pressure switch, then engine failure lights. When the engine speed is lowered to 1 936 r / min, VTEC pressure switch back to normal. Throughout the process, VTEC solenoid valve remains closed. This shows that the VTEC system is completely free to enter the work state power system control unit. Because VTEC solenoid valves and pressure switches are new members, it is likely due to failure of the hydraulic actuator valve malfunction caused.
means on VTEC found dismantling the hydraulic fracture operation for the valve return spring (FIG. 3). Hydraulic actuator valve is constantly in the ON state, the rocker arm hydraulic oil into the valve chamber in an uncontrolled state, so that the synchronization state of the piston and the pressure switch operation depends entirely on the oil pressure control of the engine without power system control unit, . This is the cause of the fault lies.
troubleshooting: After replacing VTEC assembly, troubleshooting. After a period of re-users, reflecting the fault does not occur again.
reviewed: Since VTEC is usually put to work at high engine speeds, while this fault is present, also at high engine speed, oil pressure reaches cause VTEC activated when a certain value, What is difficult to detect engine ldquo; bad phenomenon rdquo ;. This phenomenon is due to a malfunction of the car is very oftenSee fault lamp is lit, the start of repair, maintenance personnel idea is still in the inertia of thinking electrical failure, failed to fully pay attention to the logic signal HDS data stream, and take some detours. As can be seen by this maintenance, mechanical failures can find the answer by looking at data flow analysis, which open the way for future troubleshooting efforts.
(Fuyan Wei, Li Deguo)