5-6 Shift
Diagnostic trouble code P0829 indicates a malfunction in the automatic transmission's 5-6 shift operation. The transmission control module sets this code when it detects an incorrect gear ratio or failure to engage 6th gear based on input and output speed sensor data.
Transmission shifting issues should be addressed immediately to prevent internal damage. Driving with this code can lead to limp mode, poor performance, and complete transmission failure.
Common symptoms
- Illuminated Check Engine Light
- Transmission fails to shift into 6th gear
- Harsh or erratic shifting
- Transmission slipping during the 5-6 shift
- Decreased fuel economy at highway speeds
Likely causes
- Low or contaminated transmission fluid
- Faulty 5-6 shift solenoid
- Damaged wiring or loose connectors in the transmission circuit
- Defective transmission valve body
- Internal transmission mechanical failure (worn clutches or bands)
What to check before replacing parts
Check the transmission fluid level and condition.
Look for: Fluid that is low, burnt, or heavily contaminated indicates a leak or internal wear that can prevent proper hydraulic operation.
Visually inspect the transmission wiring harness and connectors.
Look for: Look for frayed wires, corrosion, or loose pins that could interrupt the signal to the shift solenoids.
Use a scan tool to monitor commanded versus actual gear and input/output speeds.
Look for: If the PCM commands 6th gear but the speed sensors show the ratio hasn't changed, the issue is confirmed as a failure to shift.
Test the 5-6 shift solenoid for proper resistance and operation.
Look for: An out-of-spec resistance reading or failure to click when energized indicates a failed solenoid.
Perform a transmission hydraulic pressure test.
Look for: Pressures lower than the manufacturer's specification can point to a failing pump, valve body issue, or internal hydraulic leak.
This page explains the generic P0829 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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