Meaning

The transmission control module has detected a sudden or critical drop in hydraulic pressure in the automatic transmission circuit. Pressure has fallen below the minimum threshold required for correct operation of the hydraulic actuators.

Common causes

• Sudden failure or damage to the transmission oil pump
• Severe internal leak (damaged clutch piston seal or main circuit seal)
• External ATF leak from transmission housing gaskets
• Pressure regulator valve stuck in the open position
• Completely clogged ATF filter cutting off flow to the pump
• ATF level dropped to zero due to undetected leak

Symptoms

• Check engine or transmission warning light on
• Transmission in limp mode or complete shutdown
• Total slippage or inability to engage any gear
• Abnormal noises from the transmission (pump cavitation)
• Rapid transmission overheating

Severity

What to do

1. Shut off the vehicle immediately if the transmission is not working
2. Check ATF level; if empty, do not start the engine
3. Inspect the transmission housing externally for obvious oil leaks
4. Measure hydraulic pressure with a gauge to confirm the pressure loss
5. Proceed with full transmission overhaul: pump, seals, valve body, and main circuit

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