P27B3
Internal Control Module Transmission Gear Select Performance
The internal gear-select interpretation logic in the transmission control module does not match external sensor inputs.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
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
Common causes
Ordered by how often each turns out to be the cause.
- Internal logic drift after firmware updatePossible
- External gear-select sensor driftPossible
Parts involved
- TCM
P27B3 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.