ⓘ Information only. This page provides general educational information about fault code P1840. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P1840 mean?
P1840 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Transmission Fluid Pressure Sensor Switch A Circuit.
Manufacturer-specific notes
Some manufacturers publish additional definitions or variations for this code. Always cross-check with your vehicle's own service documentation.
About Gearbox codes
Gearbox (transmission) codes report faults from the transmission control module: solenoid issues, fluid pressure problems, slipping clutches on dual-clutch boxes, and torque converter faults. Many trigger limp mode that locks the gearbox into a single forward gear.
P1840 is one of 643 codes in this category. Browse all Gearbox codes →
What we know about P1840 specifically
We record the SAE J2012 standardised definition and the system this code belongs to, but we have not yet published detailed driver-reported symptoms, common causes, or step-by-step diagnostic guidance for P1840.
Rather than invent that information by generating generic content from a template, we leave it out. For specific guidance, the most reliable sources are:
- •your vehicle's own service manual or manufacturer-specific technical bulletins
- •a qualified mechanic with a manufacturer-level diagnostic tool
- •a marque specialist familiar with your make and model
Codes nearby
Codes adjacent to P1840 in the P-code series. Many fault codes appear together with their neighbours because they relate to the same circuit or component.
Other Gearbox codes
Other fault codes in the same system as P1840. The ones with detailed guides have plain-English explanations, symptoms, causes, and diagnostic steps.
Spotted an issue or have something to add? Mechanics, technicians, and drivers who have first-hand experience with P1840 can submit a correction or expansion. We review every submission before publishing, mechanic submissions are prioritised.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →