What it means
The transmission control module monitors transmission operation during the shift from fifth to sixth gear. It sets this code when the shift does not occur as expected, such as when the expected gear change is not confirmed.
At a glance
- Usually lights the check-engine light
How it works
The transmission control module checks whether the transmission completes the shift from fifth to sixth gear as expected. P0829 sets when the requested 5-to-6 shift is not confirmed, which can point to a slipping or failing sixth-gear friction element.
Common causes
Most likely first.
- Worn 6th-gear friction element
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
- Record freeze-frame data and review commanded and actual gear, input and output speeds, and shift timing around the failed 5-to-6 event.
- Check transmission fluid level and condition using the manufacturer's procedure, looking for evidence of leakage or contamination.
- Inspect for related transmission codes and determine whether the fault occurs specifically during the fifth-to-sixth shift or across other shifts too.
- Use scan-tool data during a controlled road test, if safe, to confirm whether sixth gear engages or the transmission slips during that transition.
- If the fault is limited to the 5-to-6 shift and basic checks do not explain it, test the sixth-gear friction element and related hydraulic or mechanical operation to the manufacturer's procedure.
Common fixes
- Correct transmission fluid level if it is low and repair any leak found.
- Service contaminated or degraded fluid only as specified by the manufacturer.
- Repair a confirmed hydraulic or control fault preventing the fifth-to-sixth shift.
- Repair or replace worn sixth-gear friction components if testing confirms internal wear.
Can I keep driving?
Avoid hard acceleration and conditions that repeatedly command the 5-to-6 shift if it slips or shudders; continued slipping can overheat and damage the transmission. If the vehicle loses drive or shifts harshly into other gears, stop safely and arrange recovery.
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.