00256 Refrigerant Pressure/Temperature Sensor (G395): Electrical Fault / Implausible Signal

Investigate soon

The sensor is reporting a value the ECU refuses to believe, because it contradicts what the other sensors are saying.

Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.

The definition

00256: Refrigerant Pressure/Temperature Sensor (G395): Electrical Fault / Implausible Signal.

What to check first

Cheapest and fastest checks first:

Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
Check the connector at the part for corrosion, and that it is fully seated.
Clear the code and see whether it returns, and under what conditions.

What actually causes this on a VAG

G395 is the combined refrigerant pressure and temperature sender, fitted in the high-pressure side of the air conditioning circuit. The climate control module reads it to decide whether it is safe to run the compressor and how hard to drive the cooling fans. When this code is stored the usual symptom is simply no cold air, because the system takes the safe option and refuses to engage the compressor; the fans may also sit on a higher stage than you are used to. The 'implausible signal' wording is worth reading carefully, because it cuts both ways: it can mean a broken sensor, or a perfectly good sensor honestly reporting a pressure that really is wrong. Fitting a sensor to a system that is simply flat, or badly overcharged, is the single most common way money gets wasted on this code.

Most likely causes, in order

The system is low on refrigerant, or leaking. Air conditioning loses a little gas over the years and a leak makes that much faster. A pressure that has fallen outside the expected window reads as implausible to the module. Have the actual charge and the running pressures measured on gauges before any part is bought - this is the cheapest answer and the most common one.
Overcharged, or a restricted high side. The other half of 'implausible' is a pressure that is too high. A DIY top-up can that has put too much gas in, a condenser packed with leaves, flies or road dirt, or a blocked receiver drier will all push the high side up. Look at the condenser through the grille before anything is unbolted, and tell whoever gauges the system about any recent top-up - it changes what the numbers mean.
Connector or wiring at the sensor. The sender sits in engine-bay heat and vibration, often well forward where salt and stone chips reach it. Look for corroded or spread terminals, a connector that is not fully latched, and a wire chafed where the loom passes the pipe or a bracket.
The sender itself. They do fail, and it is not an expensive part - but it is the fourth thing to check, not the first, because a good sender reporting a bad pressure produces the same code.
Fault in the climate control module or the wiring back to it. Uncommon, and only a sensible conclusion once the charge, the high-side condition, the wiring and the sender have all been checked and proved good.

Worth knowing: Ask to see gauge readings before you agree to a new sensor. If the system is flat or leaking, a sensor changes nothing, and a re-gas without finding the leak buys you one summer at best. Air conditioning refrigerant is under high pressure and is a controlled gas: recovery and recharging are a job for someone with the right equipment and, in the UK and EU, the F-gas qualification to do it legally, and it must never simply be vented to atmosphere. Many VAG installations put the sender in a self-sealing port so it can be swapped without discharging the system, but have that confirmed for your car before anyone starts undoing it - if it is not self-sealing, the job becomes discharge, replace and recharge. And if the car has recently had air conditioning work, or has been standing with the system empty, clear the code and retest first: it may only be a record of that period rather than a live fault.

Reading the code is the easy part

A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.

VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.

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Common questions

What does 00256 mean?

00256 means Refrigerant Pressure/Temperature Sensor (G395): Electrical Fault / Implausible Signal. The sensor is reporting a value the ECU refuses to believe, because it contradicts what the other sensors are saying.

Can I drive with 00256?

The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.