U3978 BMW Fault Code

Description:

Variable Cam Timing Over-advanced (Bank 1) The comprehensive component monitor (CCM) monitors the VCT position for an over-advanced camshaft timing.
The test fails when the camshaft timing exceeds a maximum calibrated value or remains in an advanced position.

BMW cam timing improperly set No oil flow to the VCT piston chamber Low oil pressure VCT solenoid valve stuck closed Camshaft advance mechanism binding (VCT unit) U3978 DTC is a check of the VCT unit.

U3978 Code Symptoms :

If your U3978 check engine light is illuminated, it's best to take it in for diagnostic testing, which can feel like a hassle. Because while the lights vary in appearance from vehicle to vehicle, all have the same basic meaning: There's a problem with the car's emissions system. The on-board diagnostics system U3978 and engine control unit are in charge of monitoring a bunch of different , and if they get a reading that's a little out of whack, up pops the check engine light.

Diagnosis And Repairing U3978

U3978 OBD 2 code on vehicles with electronically controlled automatic transmissions, the 3-4 shift solenoid is responsible for actuating the hydraulic circuits to activate clutches or bands that change gears inside the automatic transmission.

How to fix U3978 code ?

• Erratic camshaft position due to low oil pressure
• Engine Control Module (ECM)
• Camshaft Position Sensor harness is open or shorted
• Fuel injectors may be faulty

Some systems require that the actuator has an adequate supply of brake fluid. Low brake fluid levels can mimic the symptoms of code U3978, so consult the manual to locate the brake fluid reservoir.

Bear in mind that a low fluid level can set code U3978 on some applications, so make sure that on fluid operated systems the fluid level is up to the mark before starting an electrical diagnosis.