P084B

What it means

P084B is the generic code for a range or performance fault in the transmission fluid pressure sensor or switch 'H' circuit. The transmission control module has seen a signal from that sensor or switch that does not match the pressure it expects for the current gear, commanded solenoid state or operating condition. The signal is still within electrical limits, so this is a plausibility fault rather than a plain open or short circuit. Which sensor or switch is 'H' depends on the manufacturer and transmission, so check the model-specific information.

Symptoms

• Gearbox warning light or malfunction indicator lamp on
• Harsh, delayed or flared gear changes
• Transmission stuck in one gear (limp mode)
• Slipping under load or when pulling away
• Erratic shift timing or unexpected gear hunting
• Reduced performance or economy

Possible causes

• Low, degraded or contaminated transmission fluid, or the wrong fluid typelikely
• Faulty pressure sensor or switch giving a drifting or implausible signallikely
• Damaged wiring, poor connector contact or corrosion in the sensor circuit (including reference voltage or earth)likely
• Sticking or worn solenoid or valve body fault causing real pressure to differ from the commanded valuepossible
• Blocked internal filter or restricted fluid passages causing low or unstable pressurepossible
• Worn clutch packs, seals or an ailing pump leaking pressure internallypossible
• Fault within the transmission control module or an outdated calibration where the manufacturer has issued an updaterare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting gear, fluid temperature, speed and load when the fault set; look for other transmission codes that point to the same cause.
2. Check the transmission fluid level and condition (where a dipstick or check procedure exists), following the manufacturer's method and temperature requirements; note any burnt smell, debris or discolouration.
3. Inspect the sensor, its connector and the wiring for damage, chafing, fluid ingress, corrosion or pushed-back pins, and check for leaks around the sensor.
4. Check the live data for the pressure sensor or switch against the commanded pressure and the specification, including with the engine off and at idle in park.
5. Test the sensor circuit for reference voltage, signal and earth, and check wiring resistance and continuity against the manufacturer's data.
6. Compare the sensor reading with a mechanical pressure test at the transmission test port, if the model has one, to separate a sensor fault from a real pressure fault.
7. Run solenoid and actuator tests where the system supports them, and check for related software updates or technical bulletins for the model.
8. If pressure is genuinely wrong, inspect the filter, valve body and pump as per the manufacturer's procedure.

How to fix

• Correct the fluid level and renew degraded fluid and filter using the specified fluid and procedure.
• Replace the faulty pressure sensor or switch, if testing proves it is out of specification.
• Repair or replace damaged wiring and connectors, and clean or repair terminals.
• Clean, repair or replace a sticking solenoid or valve body, as the model's procedure allows.
• Repair or overhaul the transmission if internal wear, seals or pump are causing low pressure.
• Apply a manufacturer calibration update to the control module only if an outdated one is a documented cause.

Can I keep driving?

Nearby codes

• P084AGenericTransmission Fluid Pressure Sensor/Switch H Circuit
• P084CGenericTransmission Fluid Pressure Sensor/Switch H Circuit Low