BMW fault 4E86 - Solenoid valve 3
P0979 · Control circuit low
4E86 is stored by the EGS when it detects a low-voltage condition on the solenoid valve 3 (shift solenoid C) control circuit. This solenoid is one of the hydraulic control valves in the transmission that directs fluid pressure to engage specific gear ratios.
The EGS detects a low voltage on the shift solenoid C control circuit, indicating an open circuit, short to ground, or a failed solenoid coil. The transmission enters emergency mode in 6th gear (CC-ID 420). The monitoring runs with ignition on and battery voltage between 7V and 16V.
- Module
- EGS
- Severity
- Critical
- Likely cause
- Failed solenoid coil in the mechatronic unit
- Common fix
- Replacing the mechatronic unit
Symptoms
- Transmission malfunction warning on the instrument cluster (CC-ID 420).
- Transmission locks into 6th gear and will not shift.
- Loss of normal gear selection.
Common causes
- Failed solenoid coil within the mechatronic unit with an open winding or internal short to ground.
- Internal mechatronic wiring fault between the electronics and the solenoid.
- Corroded or loose connector at the mechatronic interface.
Diagnosis
- Read the fault memory and check the fault frequency counter. If the frequency is greater than 2, the mechatronic unit requires replacement.
- If the fault is passive (stored but not currently active), clear the fault memory and perform a road test through all gears including upshifts and downshifts under load. If the code does not return, the transmission is operating within tolerance.
- If the code returns after clearing, the solenoid or its internal circuit has failed and the mechatronic unit needs replacement. Before committing to replacement, check the transmission fluid for signs of clutch wear (burnt smell, metallic particles). Replacing the mechatronic on a transmission with worn clutches will not resolve shifting problems.
Resolution
Replace the mechatronic unit if the fault frequency is greater than 2 or if the code returns after clearing and road testing. Replace the transmission filter and fluid during the repair. Reset the EGS adaptation values after installation. Clear the fault memory and perform an adaptation drive through all gears at varying throttle loads to confirm the code does not return.