Fault code P0040 – a step-by-step guide to diagnosing and fixing it

The meaning of error code P0040 – O2 Sensor Signals Swapped Bank 1 Sensor 1/ Bank 2 Sensor 1

P0040: Causes, signs and repairs

Error code P0040 is displayed and the check engine light is on - what does this mean?

The DTC P0040 is recognized by the OBD/EOBD system if there is a problem with the lambda sensor heating system upstream of the catalytic converter (bank 1, sensor 1). This trouble code indicates a defective heating of the oxygen sensor, as a result of which the sensor cannot reach the required operating temperature. Different manufacturers may have slightly different names for this fault code, but it always refers to the O2 sensor heater.

What causes can this fault code have?

Defective lambda sensor heater
Damaged cable to the sensor heater
Corroded or loose plug connections
Blown fuse in the heating circuit
Defective engine control unit
Short circuit in the wiring
Completely defective lambda sensor
Oxidation on the connection terminals

What symptoms occur in parallel with fault code P0040?

Increased fuel consumption: The vehicle requires more fuel than usual
Poor engine performance: Loss of power, especially when the engine is cold
Unsteady idling: Engine runs unevenly at idle speed
Starting problems: Difficulty starting the engine when cold
Exhaust problems: Increased emission values during the emissions test
Jerking when driving: Uneven engine running while driving

How to fix the P0040 fault code problem?

Repairing the P0040 fault code requires a systematic approach to identify the exact source of the fault.
Replace the lambda sensor completely, as defective heaters cannot usually be repaired separately
Check the wiring to the oxygen sensor and replace or repair damaged cables
Clean plug connections, treat with contact spray and connect firmly
Check fuses in the engine compartment and replace blown fuses
Have the engine control unit checked for defects and replace or reprogram if necessary
Carry out a multimeter measurement of the heater voltage and repair the power supply if there are deviations
Measure the resistance of the sensor heater and replace the sensor if the values are incorrect

FAQ - Frequently asked questions about DTC P0040

Can I continue driving with error code P0040?

It is possible to drive for a short time, but you should have the P0040 code rectified as soon as possible. The engine runs with an emergency program, which leads to increased consumption and poorer performance.

How much does it cost to repair error code P0040?

The cost of a P0040 repair is between 80-300 euros. A new lambda sensor costs around 50-150 euros, plus labor costs of 30-150 euros depending on the workshop and accessibility.

How long does the repair of code P0040 take?

Fixing the P0040 trouble code usually takes 30 minutes to 2 hours. The diagnosis takes about 30 minutes, the sensor replacement another 30-90 minutes depending on the vehicle model.

Can I repair the P0040 trouble code myself?

With basic knowledge, the P0040 repair is feasible. You will need an OBD diagnostic device, multimeter and the appropriate tools. If you are unsure, you should visit a specialist workshop.

Will the P0040 code return after the repair?

After proper repair, the DTC P0040 should not return. If it does, there may be an additional defect or the repair was incomplete.

What consequential damage can fault code P0040 cause?

Untreated P0040 can lead to catalytic converter damage, increased engine wear and problems with the emissions test. In the long term, repair costs will also increase considerably.

Vehicles in which error code P0040 occurs most frequently

Fault code P0040 is a common EOBD code that indicates problems with the lambda sensor heater and can occur in virtually all modern vehicles with a petrol engine, but is most common in the following vehicles:

Volkswagen: Golf, Passat, Polo, Touran, Tiguan (2000-2015)
Audi: A3, A4, A6, TT, Q5 (1998-2012)
BMW: 3 Series, 5 Series, X3, X5, Z4 (2001-2014)
Mercedes-Benz: C-Class, E-Class, A-Class, ML-Class (2000-2013)
Opel: Astra, Vectra, Corsa, Zafira, Insignia (1999-2016)
Ford: Focus, Mondeo, Fiesta, Kuga, Galaxy (2000-2014)
Toyota: Corolla, Avensis, RAV4, Auris, Yaris (1999-2015)
Honda: Civic, Accord, CR-V, Jazz, HR-V (2000-2014)
Nissan: Qashqai, X-Trail, Micra, Primera, Note (2001-2015)
Peugeot: 206, 207, 307, 308, 407, 3008 (2000-2016)

If the code P0040 occurs in your vehicle, you should first have a thorough diagnosis carried out. Many garages offer a free fault code reading, which will give you an initial estimate of the repair costs. As P0040 has similar causes for different manufacturers, the repair approaches are usually standardized and well documented.

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