P0115 indicates engine coolant temperature circuit malfunction. The exact repair depends on whether the underlying issue is a sensor fault, wiring problem, mechanical wear, or a related system problem on the vehicle being diagnosed.
This guide is reviewed against current UK fault-code usage patterns, MOT guidance, and indicative repair-cost context. It is educational guidance for P0115, not a substitute for live data, workshop testing, or a final quote.
This page explains the code in plain English and gives indicative UK repair and MOT context. It does not confirm the exact failed part. Vehicle age, engine, related codes, live data, and workshop inspection can all change the final diagnosis and quote.
P0115: coolant temp sensor circuit invalid, can mask overheating. Check coolant level and wiring first (£20-£150). When this fault is detected, the ECU (Engine Control Unit) stores the code and usually illuminates the check engine light on the dashboard.
In practice, P0115 should be treated as a cooling and temperature control problem first, not as proof that one named part has failed. The value of the code is in narrowing the system, checking related data, and avoiding the usual misdiagnosis before parts are ordered.
These are the most common symptoms UK drivers report when this code is active:
Note that some vehicles show no drivability symptoms at all — the check engine light may be the only sign. This is why scanning the fault code is essential rather than guessing at the cause.
These are typical causes to check first:
It is important to diagnose the root cause before replacing parts. Many unnecessary and expensive repairs happen because the most expensive component is replaced first without proper testing. Always work through the diagnostic steps systematically.
Work through these steps in order to avoid unnecessary parts replacement:
After any repair, clear the fault code with an OBD-II scanner and carry out a test drive. If the code returns, continue to the next diagnostic step. For a personalised repair guide specific to your vehicle's make, model, year and engine, use our AI Diagnostic Report below.
These models are frequently seen with this fault code in UK garages:
This code can appear on OBD-II compatible vehicles. OBD-II is standard on most UK petrol cars from 2001 and diesel cars from 2004, with many later-1990s vehicles also compatible. The models listed above are examples where owners and garages often encounter this fault, but they are not an exhaustive or ranked list.
Difficulty: Easy — sensor is usually accessible and inexpensive.
UK repair cost estimate: £20–£150 including parts and labour at average UK workshop rates (inc. VAT). Independent garages are typically 30–50% cheaper than main dealers. Always get at least two quotes.
Prevention: Check coolant level monthly, replace coolant every 3–5 years.
P0115 is in the engine-temperature or cooling-control family. On UK cars these faults often become more obvious in winter traffic, after coolant neglect, or when thermostat and fan-control behavior drift out of spec.
The common mistake with P0115 is assuming every cooling code is sensor-related. Real temperature behavior matters more than the dashboard light alone.
Fault code P0115 does not directly cause an MOT failure on its own, but it can still cause a failure if it keeps the check engine light (MIL) on where MIL inspection applies, or affects emissions.
Even if the light is not currently on, if the fault is intermittent it could reappear during the test. Use our AI Diagnostic Report to understand the MOT risk specific to your vehicle and get advice on whether it is safe to proceed to your test.
This guide is informed by the following authoritative UK sources:
Repair cost estimates are based on UK labour rates and parts pricing from AA, RAC and independent garage surveys, reviewed quarterly. All content is for educational purposes and is not a substitute for professional mechanical diagnosis.
Specific to your vehicle — year, make, model and engine.
Includes step-by-step repair guide, exact UK labour costs and MOT impact.
What does P0115 mean in plain English?
P0115 is a cooling and temperature control fault code. In practice, P0115 should be treated as a cooling and temperature control problem first, not as proof that one named part has failed. The code helps narrow the system, check related data, and avoid misdiagnosis before parts are ordered.
Will P0115 fail an MOT?
P0115 does not automatically fail an MOT on its own, but the underlying fault can still cause a failure if it affects safety, warning lights, or emissions.
Can I keep driving with P0115?
Drive with care and monitor the temperature gauge — a faulty coolant sensor can mask overheating.
How much does it usually cost to fix P0115 in the UK?
Typical UK repair costs for P0115 range from £20–£150, depending on the underlying fault, your exact vehicle, and local labour rates.
Use these supporting pages to compare likely repair paths, warning-light behaviour, MOT risk, and the questions to ask before approving work.
Compare P0115 with closely related faults, nearby codes in the same family, and adjacent module or sensor faults that often need to be ruled out during diagnosis.
Last updated: August 2026. AI-Diagnostics-Pro provides AI-generated information for educational purposes only. It is not a substitute for professional automotive advice. Always consult a qualified mechanic before carrying out vehicle repairs. Repair cost estimates are approximate and may vary by region and vehicle.