What it means
The transmission control module monitors the supply voltage to gear shift control module B. This code sets when that voltage falls below the module’s calibrated operating range.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Gear shift control module B operates part of the transmission's gear-selection system, and the transmission control module monitors the supply voltage feeding that module. This code sets when module B's supply falls below its calibrated operating range, which can disrupt shifts or trigger a protective gear strategy.
Common causes
Most likely first.
- Module supply fuse blown
- Wiring fault
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Read freeze-frame data and transmission codes, noting whether the low supply was recorded during a shift fault or when the vehicle was starting.
- Check the relevant module B supply fuse and verify that it is intact and seated correctly.
- Inspect module B's power and ground wiring and connectors for loose fit, corrosion, damage, or signs of heat.
- Measure supply voltage at module B and check voltage drop on its power and ground circuits under the conditions specified by the manufacturer.
- If the supply circuits pass, test module B and its control inputs using the manufacturer's diagnostic procedure.
Common fixes
- Replace a blown supply fuse after checking for the cause of the overcurrent.
- Clean, secure, or repair a loose or corroded module B power or ground connection.
- Repair damaged wiring in the module B supply circuit.
- Replace gear shift control module B only if its supply is correct and testing confirms an internal fault.
Can I keep driving?
Avoid driving if shifts are missing, the transmission slips, or the vehicle is locked in one gear; arrange recovery if control is unpredictable. Continued operation with poor shifting can worsen drivability and may damage the transmission.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.