Low, degraded or contaminated transmission fluid affecting hydraulic pressure; Faulty or sticking shift solenoid or pressure control solenoid for the 5-6 shift; Wiring or connector damage, corrosion or poor earth in the transmission harness; Worn valve body, blocked internal passages or fluid filter restriction; Faulty input or output speed sensor giving an inaccurate ratio reading; Worn clutch pack or internal mechanical wear in the gearbox, which varies by model; Outdated transmission control module software or internal module fault.

P0829

5-6 Shift.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
8: AreaTransmission
29: FaultThe specific fault in that area

What it means

P0829 is the generic SAE J2012 code for a 5-6 Shift fault, meaning the transmission control module has detected a problem when the gearbox changes between fifth and sixth gear. The control unit normally compares input and output shaft speeds against the expected ratio, or monitors the shift actuator or solenoid circuit, and sets the code when the shift fails to complete as commanded. The exact monitoring method and the components involved vary by gearbox design and manufacturer.

Symptoms

Harsh, delayed or flared shift between fifth and sixth gear
Gearbox stuck in fifth gear or unable to select sixth
Transmission warning light or engine management light on
Gearbox going into limp mode with limited gears
Poor fuel economy or higher engine revs at cruising speed
Slipping or juddering when changing up at motorway speeds

Possible causes

Low, degraded or contaminated transmission fluid affecting hydraulic pressurelikely
Faulty or sticking shift solenoid or pressure control solenoid for the 5-6 shiftlikely
Wiring or connector damage, corrosion or poor earth in the transmission harnesspossible
Worn valve body, blocked internal passages or fluid filter restrictionpossible
Faulty input or output speed sensor giving an inaccurate ratio readingpossible
Worn clutch pack or internal mechanical wear in the gearbox, which varies by modelpossible
Outdated transmission control module software or internal module faultrare

How to diagnose

Read all stored and pending codes and review freeze frame data for road speed, load, gear and fluid temperature when the fault set
Check for related codes such as speed sensor, solenoid or ratio faults, and note the order they appeared
Check the transmission fluid level and condition against the manufacturer's procedure, looking for burnt smell, dark colour or debris
Inspect the transmission wiring harness and connectors for chafing, fluid ingress, corrosion and loose pins
Check the supply voltage and earths to the transmission control module and the battery condition
Use live data to compare input and output speed, commanded gear and actual ratio during a road test through fifth to sixth
Test solenoid resistance and operation against the manufacturer's specification for your model
Check whether a software update is listed for the transmission control module for this vehicle

How to fix

Correct the fluid level or replace the fluid and filter using the specified type and procedure
Replace the faulty shift or pressure control solenoid, or the solenoid pack where it is supplied as one unit
Repair or replace damaged wiring, connectors or earths in the transmission harness
Replace a faulty input or output speed sensor
Overhaul or replace the valve body or internal components if wear or blockage is confirmed
Update or replace the transmission control module software only if an outdated calibration is a documented cause for the vehicle

Can I keep driving?

Medium severity

The car can usually be driven short distances carefully, but avoid heavy loads and long motorway runs until it is checked. Continued driving with a shift fault or slipping can cause further internal gearbox damage, so book it in soon.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.