B21F7

Symptoms

• The gear selector does not respond to commands
• Unable to change gears manually
• Car gets stuck in one gear
• Check Engine Light and Transmission Warning Light Illuminates
• Strange sounds from the selector when trying to shift
• Loss of power inside the car
• The car may not start or stall when shifting

Causes

• Damaged or frayed selector lever harness wire insulation
• Oxidation or corrosion of selector connector contacts
• Moisture in the connector or selector module
• Malfunction of the electronic selector itself (internal short circuit)
• Damage or failure of the selector power relay module
• Incorrect assembly or reconnection of the wiring harness after repair
• Defective transmission control module (TCM) or ECU
• Short circuit inside the dashboard switch panel

How to Fix

1. Connect an OBD-II scanner and read the full set of errors to clarify the diagnosis
2. Visually inspect the selector wire harness for damage, cracks in insulation, moisture
3. Check the connector of the selector and control module for oxidation, corrosion, contact play
4. Measure the resistance between the conductor and ground in the selector harness (should be high, at least MOhm)
5. Check the supply voltage at the selector connector (usually 12V DC)
6. If necessary, disassemble the connectors and clean the contacts from oxidation using special means
7. If the wiring harness is damaged, replace it with a new one or repair the damaged area.
8. Check the serviceability of the selector power relay module or replace it
9. Carry out diagnostics of the transmission control module and ECU, reprogram if necessary
10. If the selector itself is faulty, replace it with an original one.
11. Clear the error with a scanner and conduct a test drive to confirm the solution to the problem

Related codes

FAQ