Automatic transmission slipping or harsh shifts
Transmission hangs between gears, RPMs climb but the car doesn't accelerate — symptoms and OBD-II codes.
Transmission slip means the engine revs but the car doesn't respond with matching acceleration. You feel a "delay" or a clunk on shift engagement. It's an early warning sign — address it before the trans fails completely.
Main causes: (1) low or degraded ATF; (2) dirty valve body; (3) worn clutch pack friction material; (4) faulty pressure or shift solenoid.
OBD-II will throw P07xx or P08xx codes (TCM fault). Also check VSS (vehicle speed sensor) — if ECU and TCM see different speeds, shifts go wrong.
First diagnostic steps
- Check ATF level and colour (should be clear red or pink)
- Read TCM codes (often a separate module from the ECU)
- Monitor live TPS and VSS during acceleration
- Check live ATF temperature (keep it under 190°F / 90°C)
- Note exactly which gear ratios slip
Likely fault codes
Click a code for detailed description, causes, and diagnostic plan.