U0404

What it means

The Gear Shift Control Module is present on the data bus but the values it reports are implausible — out of range, frozen, or failing the checksum or rolling-count check. The receiving modules reject the data. Shift-by-wire gear selection may be wrong or blocked. Causes include a faulty sensor feeding the module, internal computation errors, a software or calibration mismatch after a repair, or bus interference corrupting the frames.

Is it safe to drive?

This code can put the vehicle into limp or reduced-power mode. Avoid extended driving and have the vehicle diagnosed promptly.

Most likely causes

• Shift module internal fault

  medium

  A plausible cause — test and verify before replacing parts.

• CAN corruption causing checksum errors

  medium

  A plausible cause — test and verify before replacing parts.

• Gateway module routing CAN messages incorrectly

  low

  Less common, but worth ruling out after the more likely causes.

Related help

• Full U0404 diagnosis, causes & costs
• How to read check engine light codes
• Is it safe to drive with the light on?